WEBVTT 00:00:00.080 --> 00:00:01.670 The following content is provided 00:00:01.670 --> 00:00:03.820 under a Creative Commons license. 00:00:03.820 --> 00:00:06.550 Your support will help MIT OpenCourseWare continue 00:00:06.550 --> 00:00:10.160 to offer high quality educational resources for free. 00:00:10.160 --> 00:00:12.700 To make a donation or to view additional materials 00:00:12.700 --> 00:00:16.620 from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:16.620 --> 00:00:17.275 at ocw.mit.edu. 00:00:26.040 --> 00:00:28.010 PROFESSOR: OK, I guess we'll get started. 00:00:28.010 --> 00:00:33.270 Last time, we were talking about the auditory pathway 00:00:33.270 --> 00:00:38.660 in the brain, the central auditory pathway, 00:00:38.660 --> 00:00:40.850 starting with the cochlear nucleus 00:00:40.850 --> 00:00:42.970 and going up through the various brain 00:00:42.970 --> 00:00:46.690 stem, the thalamic and cortical auditory areas. 00:00:47.780 --> 00:00:51.070 And then we focused mainly on the cochlear nucleus, 00:00:51.070 --> 00:00:55.280 which is the very first of those many auditory central nuclei. 00:00:55.280 --> 00:00:59.220 And we talked about the diversity 00:00:59.220 --> 00:01:03.930 of cell types or neuron types in the cochlear nucleus 00:01:03.930 --> 00:01:07.230 and the diversity of response types 00:01:07.230 --> 00:01:11.950 when you monitor the responses of single neurons to sound. 00:01:13.580 --> 00:01:17.930 And we did some attempts at correlation between the two. 00:01:17.930 --> 00:01:20.530 And those are firmly established in the cochlear nucleus, 00:01:20.530 --> 00:01:23.080 much better than anywhere else in the auditory 00:01:23.080 --> 00:01:24.330 pathways certainly. 00:01:24.330 --> 00:01:28.470 So any questions from last time? 00:01:34.060 --> 00:01:40.500 So today's lecture is on hearing loss and implants that 00:01:40.500 --> 00:01:43.800 restore our sense of hearing if we happen to be deaf. 00:01:45.280 --> 00:01:47.510 And I've written a little summary 00:01:47.510 --> 00:01:50.550 of what I want to cover today on the board. 00:01:50.550 --> 00:01:54.350 So we'll start out with the first 2/3 of the lecture being 00:01:54.350 --> 00:01:55.270 on hearing loss. 00:01:56.840 --> 00:02:01.740 And we've mentioned a little about the conductive apparatus, 00:02:01.740 --> 00:02:07.220 the eardrum, the three ossicles in the middle ear, 00:02:07.220 --> 00:02:10.320 conveying the vibrations to the inner ear. 00:02:10.320 --> 00:02:15.100 And I think we had an example of one type of conductive hearing 00:02:15.100 --> 00:02:16.020 loss. 00:02:16.020 --> 00:02:19.630 If you have, obviously, an interruption of that ossicular 00:02:19.630 --> 00:02:23.650 chain, then the vibrations are going 00:02:23.650 --> 00:02:27.469 to be reduced in the inner ear in the conduction pah-- 00:02:27.469 --> 00:02:29.260 because the conduction path is interrupted. 00:02:30.360 --> 00:02:35.970 So those are relatively straightforward concepts, 00:02:35.970 --> 00:02:38.580 and so consider those covered. 00:02:38.580 --> 00:02:41.950 Today, I want to talk about the, perhaps, 00:02:41.950 --> 00:02:44.820 more common types of hearing loss 00:02:44.820 --> 00:02:47.900 that are grouped under the name sensorineural 00:02:47.900 --> 00:02:54.060 because the sensory cells, or the nerve fibers themselves, 00:02:54.060 --> 00:02:54.570 are damaged. 00:02:55.930 --> 00:02:59.110 And in that case, it's not so easy to understand 00:02:59.110 --> 00:03:01.710 how we might correct them by putting 00:03:01.710 --> 00:03:06.340 in an artificial middle ear ossicle or something like that. 00:03:07.510 --> 00:03:14.360 This is a bit of a misnomer in that perhaps 99% of hearing 00:03:14.360 --> 00:03:17.610 loss and deafness of this type was really 00:03:17.610 --> 00:03:21.675 based on the sensory cells, so the hair cells 00:03:21.675 --> 00:03:25.521 are the prime culprit in people who have sensorineural hearing 00:03:25.521 --> 00:03:26.020 loss. 00:03:28.360 --> 00:03:30.845 The most vulnerable, of the two types 00:03:30.845 --> 00:03:32.470 of hair cells we've been talking about, 00:03:32.470 --> 00:03:33.715 are the outer hair cells. 00:03:35.000 --> 00:03:39.070 Any of the various causes that we'll talk about that damage 00:03:39.070 --> 00:03:41.470 our hearing affect the outer hair 00:03:41.470 --> 00:03:44.960 cells to a much greater degree than the inner hair cells, 00:03:44.960 --> 00:03:47.614 and the reason for that is not known. 00:03:47.614 --> 00:03:50.030 For some reason, the outer hair cells are more vulnerable. 00:03:51.270 --> 00:03:55.340 As we'll see in the very first slide of today's lecture, 00:03:55.340 --> 00:03:59.070 those hair cells in the basal turn of the cochlea 00:03:59.070 --> 00:04:02.215 are more vulnerable than those in more a apical regions. 00:04:03.670 --> 00:04:05.980 Reason for that is not known either. 00:04:05.980 --> 00:04:10.870 It's a very interesting phenomenon with no basis 00:04:10.870 --> 00:04:12.550 that we know about. 00:04:12.550 --> 00:04:16.430 We'll talk about permanent and temporary hearing 00:04:16.430 --> 00:04:20.410 loss, the various causes of hearing loss, 00:04:20.410 --> 00:04:23.580 and then, at the end, we'll talk about the various neural 00:04:23.580 --> 00:04:27.265 prostheses, or implants, that are used to restore hearing. 00:04:28.674 --> 00:04:30.340 And the most famous of those, of course, 00:04:30.340 --> 00:04:32.230 is the cochlear implant. 00:04:32.230 --> 00:04:35.580 We hope to have a visit from a subject who's 00:04:35.580 --> 00:04:38.680 deaf, who uses a cochlear implant, 00:04:38.680 --> 00:04:42.187 and she'll be able to demonstrate her implant to you 00:04:42.187 --> 00:04:46.170 and answer questions if you want to ask them of her 00:04:46.170 --> 00:04:47.790 about her cochlear implant. 00:04:47.790 --> 00:04:50.700 We'll also cover a couple other different types 00:04:50.700 --> 00:04:53.100 of implants that are used to restore hearing. 00:04:55.860 --> 00:05:00.520 So this first slide talks about sensorineural hearing loss 00:05:00.520 --> 00:05:01.020 in general. 00:05:02.570 --> 00:05:07.220 And a very common pattern of sensorineural hearing loss, 00:05:07.220 --> 00:05:10.190 which comes from the basal turn being most affected. 00:05:12.070 --> 00:05:14.210 This is an audiogram, if you will, 00:05:14.210 --> 00:05:20.130 a graph of hearing level in terms of sound pressure level, 00:05:20.130 --> 00:05:24.900 hearing threshold as a function of sound frequency for, 00:05:24.900 --> 00:05:27.760 in this lower curve, a normal hearing 00:05:27.760 --> 00:05:33.280 human and, in this upper curve, a typical pattern for someone 00:05:33.280 --> 00:05:38.015 who has a mild to moderate sensorineural hearing loss. 00:05:39.050 --> 00:05:42.410 And so as you can see, this individual 00:05:42.410 --> 00:05:45.230 with the hearing loss has perfectly normal hearing 00:05:45.230 --> 00:05:50.070 thresholds up to the middle frequency, 1,000 Hertz, 00:05:50.070 --> 00:05:52.470 but then their threshold of hearing 00:05:52.470 --> 00:05:56.260 deviates from the normal so that by about 10,000 Hertz, 00:05:56.260 --> 00:05:59.570 they have a hearing loss of 60 dB or so. 00:05:59.570 --> 00:06:03.590 This is a very common pattern of hearing loss that 00:06:03.590 --> 00:06:07.530 arises because, for some reason, the basal turn is 00:06:07.530 --> 00:06:08.205 more affected. 00:06:09.910 --> 00:06:12.660 The basal turn is where you have the responses 00:06:12.660 --> 00:06:14.486 to the very highest sound frequencies. 00:06:17.630 --> 00:06:21.810 This person will come into the Massachussetts Eye and Ear 00:06:21.810 --> 00:06:26.740 Infirmary, for example, and complain to the doctors 00:06:26.740 --> 00:06:30.200 and audiologists there when the hearing loss becomes 00:06:30.200 --> 00:06:34.160 noticeable, when they have a problem understanding speech. 00:06:35.710 --> 00:06:39.950 Hearing loss is intimately entwined 00:06:39.950 --> 00:06:43.230 with our perception and understanding of speech. 00:06:44.360 --> 00:06:49.090 And so when people have problems understanding speech, 00:06:49.090 --> 00:06:51.080 they often seek medical advice. 00:06:51.080 --> 00:06:56.530 Now, the most important frequencies for those in speech 00:06:56.530 --> 00:07:00.230 are between about 300 and 4,000 Hertz. 00:07:00.230 --> 00:07:03.070 So you can see this person's hearing loss is clearly 00:07:03.070 --> 00:07:07.210 getting into the speech range, and they 00:07:07.210 --> 00:07:10.560 may have problems discerning the more high frequency 00:07:10.560 --> 00:07:11.540 parts of speech. 00:07:11.540 --> 00:07:12.970 So what are those? 00:07:12.970 --> 00:07:18.800 So typically vowels, which have the formants that we talk 00:07:18.800 --> 00:07:21.940 about, have very low frequency, so something 00:07:21.940 --> 00:07:24.015 like ahhh and oooh. 00:07:24.015 --> 00:07:25.265 They are very low frequencies. 00:07:27.190 --> 00:07:29.850 But I think if you could read this diagram a little better, 00:07:29.850 --> 00:07:33.020 you'd understand that high-pitched sounds 00:07:33.020 --> 00:07:37.690 like the "sss" sound of an s, or something 00:07:37.690 --> 00:07:40.950 that has an abrupt onset, like a "t", 00:07:40.950 --> 00:07:43.440 has a lot of high frequencies in that sound. 00:07:44.470 --> 00:07:49.510 And so those are going to be the first types of speech sounds 00:07:49.510 --> 00:07:51.620 that are hard to understand for the person 00:07:51.620 --> 00:07:56.870 with the impaired graph on the top slide there. 00:07:58.330 --> 00:08:01.220 Now at first, you might say, well, 00:08:01.220 --> 00:08:05.610 what we should do is get a hearing aid that amplifies 00:08:05.610 --> 00:08:10.810 the frequencies that are in loss area OK. 00:08:10.810 --> 00:08:13.070 So to do that, you'd have to have 00:08:13.070 --> 00:08:15.190 a pretty sophisticated hearing aid. 00:08:15.190 --> 00:08:18.490 You'd have to, for each sound frequency, 00:08:18.490 --> 00:08:21.680 dial in the exact amount of amplification. 00:08:21.680 --> 00:08:25.450 And hearing aids are very good these days, 00:08:25.450 --> 00:08:30.260 and there are hearing aids that can be used on a frequency 00:08:30.260 --> 00:08:33.179 specific manner, that is don't amplify anything 00:08:33.179 --> 00:08:37.277 at low frequencies and amplify exactly the amount of loss 00:08:37.277 --> 00:08:38.110 at high frequencies. 00:08:39.250 --> 00:08:41.750 So at first, it sounds like a good idea, 00:08:41.750 --> 00:08:46.040 but we'll get into the reason that that doesn't always 00:08:46.040 --> 00:08:49.480 work later on. 00:08:49.480 --> 00:08:54.460 So that simple solution, just install a hearing aid-- 00:08:54.460 --> 00:08:59.130 a hearing aid, which everybody has seen one probably in older 00:08:59.130 --> 00:09:02.560 people-- is simply an amplifier. 00:09:02.560 --> 00:09:03.775 It has a microphone. 00:09:03.775 --> 00:09:04.910 It picks up sound. 00:09:06.030 --> 00:09:10.100 It boosts the sound in whatever frequency 00:09:10.100 --> 00:09:12.850 ranges the audiologist programs. 00:09:12.850 --> 00:09:17.710 And then it has a little speaker and it speaks or plays 00:09:17.710 --> 00:09:20.847 the boosted sound into the ear canal of the person. 00:09:20.847 --> 00:09:21.930 So it's just an amplifier. 00:09:24.100 --> 00:09:29.140 So you can have hearing aids that work very well 00:09:29.140 --> 00:09:31.360 and their frequency tailored. 00:09:31.360 --> 00:09:33.580 And they especially work very well 00:09:33.580 --> 00:09:35.200 for the type of hearing loss that's 00:09:35.200 --> 00:09:39.350 called the conductive hearing loss because, simply, 00:09:39.350 --> 00:09:43.080 the problem is getting the sound into the inner ear, 00:09:43.080 --> 00:09:46.550 and amplifying the sound, in a person 00:09:46.550 --> 00:09:49.580 with a conductive hearing loss, works very well. 00:09:49.580 --> 00:09:52.520 It doesn't work so well in sensorineural hearing 00:09:52.520 --> 00:09:54.940 loss for reasons we'll get into in a little bit. 00:09:59.530 --> 00:10:02.120 Now how do these hearing losses happen? 00:10:02.120 --> 00:10:07.690 There are a variety of causes that can damage your hearing. 00:10:08.870 --> 00:10:12.360 We all have fun with sounds, and we tend to have a lot of fun 00:10:12.360 --> 00:10:13.845 when the sounds are very intense. 00:10:14.990 --> 00:10:18.790 And these are so-- this is an old transparency obviously. 00:10:18.790 --> 00:10:23.310 But this is a graph of sound pressure level here. 00:10:23.310 --> 00:10:26.940 Remember the thresholds of hearing are way down here. 00:10:26.940 --> 00:10:28.660 And these are some example sounds 00:10:28.660 --> 00:10:32.240 that have very high level, and most of these 00:10:32.240 --> 00:10:36.520 are damaging, at least if you listen to them long enough. 00:10:36.520 --> 00:10:42.250 Obviously, gunshots, firecrackers are very damaging. 00:10:42.250 --> 00:10:45.920 Those sounds are in excess of 120 dB. 00:10:45.920 --> 00:10:50.320 So a single gunshot, if it's close to your head, 00:10:50.320 --> 00:10:51.520 can be damaging. 00:10:51.520 --> 00:10:56.340 So we had-- we're going to have an example of that 00:10:56.340 --> 00:10:57.730 in just a minute. 00:10:57.730 --> 00:11:00.380 Some of these sounds are more moderate, 00:11:00.380 --> 00:11:05.710 around the region of 100 dB SPL, for example, a chainsaw, a leaf 00:11:05.710 --> 00:11:09.300 blower, the symphony orchestra here. 00:11:09.300 --> 00:11:11.470 So everybody goes to the symphony, right? 00:11:11.470 --> 00:11:14.650 So obviously, these things depend 00:11:14.650 --> 00:11:17.410 on how close you are to the object that's 00:11:17.410 --> 00:11:19.090 generating the sound, right? 00:11:19.090 --> 00:11:20.600 So if you go to the Boston Symphony, 00:11:20.600 --> 00:11:22.350 you're not going to endure a hearing loss. 00:11:22.350 --> 00:11:25.360 But if you have good seats and are looking down 00:11:25.360 --> 00:11:28.430 on the symphony, you'll see that a lot of the woodwind 00:11:28.430 --> 00:11:31.190 players who are sitting right in front of the brass, 00:11:31.190 --> 00:11:33.570 for example, the trumpet players, they 00:11:33.570 --> 00:11:35.620 have a little screen behind them, 00:11:35.620 --> 00:11:38.360 a plexiglass screen that's pretty invisible unless you're 00:11:38.360 --> 00:11:39.590 looking for it. 00:11:39.590 --> 00:11:43.980 That causes a sound shadow, and so it protects their ears 00:11:43.980 --> 00:11:45.480 from the blast of the bras. 00:11:46.720 --> 00:11:48.212 And I've also been in the symphony 00:11:48.212 --> 00:11:50.420 where, sometimes, the woodwind players would actually 00:11:50.420 --> 00:11:53.450 put in ear plugs when there's a big brass solo, 00:11:53.450 --> 00:11:56.229 and brass is blowing like crazy. 00:11:56.229 --> 00:11:58.270 And then after that big solo, they take them out, 00:11:58.270 --> 00:12:00.300 and they play their own little solo. 00:12:01.430 --> 00:12:03.550 So professional musicians are obviously 00:12:03.550 --> 00:12:05.220 very worried about their hearing. 00:12:05.220 --> 00:12:09.730 And it can be, if you're close to a trumpet or a brass 00:12:09.730 --> 00:12:13.600 instrument, deafening-- or in front of a big timpani 00:12:13.600 --> 00:12:18.570 or snare drums-- of course, these things 00:12:18.570 --> 00:12:21.910 depend on how long you listen to them, 00:12:21.910 --> 00:12:23.690 so the damage is cumulative. 00:12:23.690 --> 00:12:27.440 It may take many years of exposure at 90 dB 00:12:27.440 --> 00:12:30.640 to produce a hearing loss even though exposure 00:12:30.640 --> 00:12:33.610 to a really high sound level, like the 160 dB, 00:12:33.610 --> 00:12:38.290 may give you hearing loss after just a single exposure. 00:12:38.290 --> 00:12:40.000 So legally, employers are supposed 00:12:40.000 --> 00:12:42.230 to provide hearing protection for their workers 00:12:42.230 --> 00:12:47.760 if you send a worker in to an 85 dB 00:12:47.760 --> 00:12:50.140 sound pressure level environment, like is 00:12:50.140 --> 00:12:52.630 common in a factory, you are supposed 00:12:52.630 --> 00:12:55.070 to provide the workers with hearing protection 00:12:55.070 --> 00:12:57.000 if it's an 8 hour shift. 00:12:57.000 --> 00:12:59.270 If it's only a 4 hour shift, you don't have to. 00:13:01.000 --> 00:13:05.740 If the sound level is 95 dB, it's something like 2 hours. 00:13:05.740 --> 00:13:10.650 If it's 100 dB, you can expose someone to an hour of that 00:13:10.650 --> 00:13:14.590 without hearing protection, but if it's longer than that, 00:13:14.590 --> 00:13:16.220 you have to provide hearing protection. 00:13:19.450 --> 00:13:20.570 So here's some example. 00:13:20.570 --> 00:13:24.030 Movie theaters, Godzilla is 118 dB 00:13:24.030 --> 00:13:25.685 because it's a terrible roar. 00:13:26.910 --> 00:13:29.960 It can be deafening if you are right near the loudspeaker. 00:13:29.960 --> 00:13:31.901 And if you go to Godzilla 100 times. 00:13:31.901 --> 00:13:32.400 OK? 00:13:34.750 --> 00:13:35.830 All right. 00:13:35.830 --> 00:13:41.340 So loud sound is one of the causes of hearing loss, 00:13:41.340 --> 00:13:43.130 so let's just make a little list here. 00:13:58.210 --> 00:14:00.310 High level sound is certainly one 00:14:00.310 --> 00:14:02.040 of the causes of hearing loss, and I 00:14:02.040 --> 00:14:05.780 think we have some examples here. 00:14:05.780 --> 00:14:11.830 So this is an example from some research that 00:14:11.830 --> 00:14:14.690 was done by one of the professors I had 00:14:14.690 --> 00:14:17.340 in graduate school, Joe Hawkins. 00:14:17.340 --> 00:14:21.790 And he studied temporal bones where 00:14:21.790 --> 00:14:24.250 the cochlear is in humans. 00:14:24.250 --> 00:14:28.190 So he would get temporal bones after a subject had passed away 00:14:28.190 --> 00:14:30.670 and had donated their body to science. 00:14:30.670 --> 00:14:34.940 And they were useful if he knew something about the individual, 00:14:34.940 --> 00:14:37.460 like if they had their hearing tested 00:14:37.460 --> 00:14:39.741 or if you knew a little bit about what activities 00:14:39.741 --> 00:14:40.240 they liked. 00:14:42.580 --> 00:14:44.690 These particular data are from a human 00:14:44.690 --> 00:14:48.260 who is an active hunter, fired a gun a lot. 00:14:51.270 --> 00:14:56.070 And the specimens shown in the photomicrographs 00:14:56.070 --> 00:14:59.170 here are looking down onto the surface 00:14:59.170 --> 00:15:04.670 of the inner ear, or cochlea, on the left side 00:15:04.670 --> 00:15:06.256 and the right side of the subject. 00:15:08.030 --> 00:15:11.860 The bone that's on the snail shell, or cochlea, 00:15:11.860 --> 00:15:14.650 has been thinned away with a dental drill, 00:15:14.650 --> 00:15:18.740 and you can see very nicely the basal turn. 00:15:18.740 --> 00:15:21.310 The apical turn, you can't really see very well from that, 00:15:21.310 --> 00:15:24.280 but you can thin the apical turn as well. 00:15:24.280 --> 00:15:24.780 Sometimes. 00:15:24.780 --> 00:15:27.150 It's cut off and thinned in a different dish. 00:15:28.600 --> 00:15:30.620 But anyway, what you're looking at here-- 00:15:30.620 --> 00:15:33.395 I should get out my pointer, so I point a little better. 00:15:40.950 --> 00:15:45.990 So this is the very basal end of the cochlea and spiraling up. 00:15:45.990 --> 00:15:49.730 And the human has about 2 and 1/2 or 3 complete turns 00:15:49.730 --> 00:15:50.355 of the cochlea. 00:15:51.610 --> 00:15:55.600 And this white structure here is the organ 00:15:55.600 --> 00:15:57.725 of Corti sitting on the basilar membrane. 00:16:00.740 --> 00:16:04.790 This specimen is stained with a stain called osmium, which 00:16:04.790 --> 00:16:09.630 stains lipids and especially myelinated nerve fibers, 00:16:09.630 --> 00:16:12.900 so you can see a lot of myelinated nerve fibers. 00:16:12.900 --> 00:16:15.690 They looks like threads coming out. 00:16:15.690 --> 00:16:17.375 And here's some more threads up here. 00:16:18.460 --> 00:16:22.100 And I said the organ of Corti is here, 00:16:22.100 --> 00:16:26.200 but actually, it's completely gone here on the left side, 00:16:26.200 --> 00:16:29.190 and you can see it begin right about here 00:16:29.190 --> 00:16:32.660 and go apically here up into the apical turn. 00:16:32.660 --> 00:16:34.470 You can see a very little bit of it 00:16:34.470 --> 00:16:38.340 in the extreme basal part of the cochlea, 00:16:38.340 --> 00:16:40.720 and that's diagrammed here on this graph. 00:16:40.720 --> 00:16:44.930 This is the length along the basilar membrane 00:16:44.930 --> 00:16:48.470 from the base over here on the right to the apex. 00:16:49.560 --> 00:16:53.084 And this y-axis graphs the percent of the hair cells 00:16:53.084 --> 00:16:53.875 that are remaining. 00:16:54.950 --> 00:16:57.820 And in the basal turn, they're almost 00:16:57.820 --> 00:16:59.930 zero hair cells remaining. 00:16:59.930 --> 00:17:01.450 They're all gone. 00:17:01.450 --> 00:17:04.770 Maybe a couple little islands here and there, 00:17:04.770 --> 00:17:08.089 but it's virtually 100% hair cell loss. 00:17:08.089 --> 00:17:11.619 And as you go around the upper basal turn, 00:17:11.619 --> 00:17:13.819 you have most of the hair cells remaining 00:17:13.819 --> 00:17:16.904 in the case of the solid line, which refers to the inner hair 00:17:16.904 --> 00:17:17.404 cells. 00:17:18.579 --> 00:17:21.300 And then you have, in the dashed lines, the three 00:17:21.300 --> 00:17:24.869 rows of outer hair cells, and there, maybe 00:17:24.869 --> 00:17:28.760 between 30% and 70% remaining depending 00:17:28.760 --> 00:17:29.860 exactly where you are. 00:17:29.860 --> 00:17:33.230 But here again, something has damaged these hair cells, 00:17:33.230 --> 00:17:36.650 completely wiped them out in the basal half of the cochlea. 00:17:36.650 --> 00:17:38.760 And wiped a lot of the outer hair cells 00:17:38.760 --> 00:17:42.250 out and not very many of the inner hair cells are wiped out. 00:17:43.890 --> 00:17:46.794 Here's the subject's right cochlea. 00:17:46.794 --> 00:17:48.710 And in this case, you can see-- you don't even 00:17:48.710 --> 00:17:51.670 need the graph-- you can see that the organ of Corti 00:17:51.670 --> 00:17:54.470 is pretty intact. 00:17:54.470 --> 00:17:57.790 Here is a little island of loss, and then 00:17:57.790 --> 00:17:59.920 another little island of loss, but then you 00:17:59.920 --> 00:18:03.840 have an intact organ of Corti all the way up to the apex, 00:18:03.840 --> 00:18:08.030 and that's reflected in the counts here where you have, 00:18:08.030 --> 00:18:11.460 except at the very basal part of the cochlea which 00:18:11.460 --> 00:18:13.460 doesn't appear in the micrograph, 00:18:13.460 --> 00:18:16.400 you have a pretty normal complement of inner hair cells. 00:18:17.697 --> 00:18:19.530 Outer hair cells are not in such good shape, 00:18:19.530 --> 00:18:23.280 but they're present throughout the cochlea in this right side. 00:18:24.290 --> 00:18:28.470 Now, also on here are graphs of the nerve fibers. 00:18:29.720 --> 00:18:33.380 Those are these little thread-like stained elements 00:18:33.380 --> 00:18:36.600 here that appear very nicely in this osmium stain, 00:18:36.600 --> 00:18:41.500 and they're pretty much intact through the cochlea. 00:18:41.500 --> 00:18:45.040 Maybe in places here where the hair cell loss is really bad, 00:18:45.040 --> 00:18:46.700 some of the nerve fibers are gone, 00:18:46.700 --> 00:18:49.270 and that's indicated by this interruption here. 00:18:49.270 --> 00:18:51.470 But this is another example where 00:18:51.470 --> 00:18:56.890 you can have whatever damaged this fellow's hair cells, left 00:18:56.890 --> 00:18:59.550 the nerve fibers relatively intact. 00:18:59.550 --> 00:19:01.630 And this offers some hope to somebody 00:19:01.630 --> 00:19:05.430 who wants to install a prosthesis like the cochlear 00:19:05.430 --> 00:19:09.029 implant and stimulate the remaining nerve fiber just 00:19:09.029 --> 00:19:10.570 because they're going to stick around 00:19:10.570 --> 00:19:12.740 even if a lot of the hair cells are gone. 00:19:14.100 --> 00:19:18.730 So this subject, as I said, was an enthusiastic hunter, 00:19:18.730 --> 00:19:20.310 and a he was right-handed. 00:19:21.540 --> 00:19:24.010 And as you can see right here, this 00:19:24.010 --> 00:19:26.480 is a top view of a person firing a rifle. 00:19:27.820 --> 00:19:30.500 The left ear of the subject is pointed 00:19:30.500 --> 00:19:32.300 toward the tip of the gun, and that's 00:19:32.300 --> 00:19:33.820 where the bullet emerges, and that's 00:19:33.820 --> 00:19:37.790 where the shock wave of the rifle, when it fires, 00:19:37.790 --> 00:19:38.500 comes out. 00:19:38.500 --> 00:19:42.820 This is a modern rifle, not a flintlock rifle 00:19:42.820 --> 00:19:45.580 where you have a lot of smoke and sound coming out down here. 00:19:45.580 --> 00:19:48.090 Most of the sound comes at the tip of the gun. 00:19:48.090 --> 00:19:51.340 And this subject's left ear is pointed right to that 00:19:51.340 --> 00:19:53.640 and has taken the brunt of the blast 00:19:53.640 --> 00:19:56.240 in terms of the loss of hair cells. 00:19:56.240 --> 00:20:00.010 The right ear of the subject is pointed more away 00:20:00.010 --> 00:20:01.950 from the tip of the gun and is protected 00:20:01.950 --> 00:20:05.560 and has a pretty normal complement of hair cells. 00:20:05.560 --> 00:20:08.370 Now, that's not saying that this person didn't 00:20:08.370 --> 00:20:11.560 go to lots of rock concerts, and didn't 00:20:11.560 --> 00:20:14.050 take lots of drugs that damage your hearing, 00:20:14.050 --> 00:20:17.840 and isn't an 80-year-old person, so we're 00:20:17.840 --> 00:20:20.230 going to add a few things to our list here. 00:20:24.780 --> 00:20:33.020 There are some drugs, for example aminoglycoside 00:20:33.020 --> 00:20:42.010 antibiotics-- they are really great antibiotics, 00:20:42.010 --> 00:20:45.800 but they have this side effect of damaging the hair cells. 00:20:47.610 --> 00:20:55.570 Three, the aging process damages hearing. 00:20:55.570 --> 00:21:01.300 And in this kind of a study where you're using a human, 00:21:01.300 --> 00:21:05.470 you cannot control for these other factors and others that I 00:21:05.470 --> 00:21:11.230 haven't, but what you can do then is compare left to right. 00:21:11.230 --> 00:21:14.730 Because presumably, a subject took drugs, 00:21:14.730 --> 00:21:17.565 and they appeared in both the left and right in your ears. 00:21:18.750 --> 00:21:23.010 And obviously, the subject had the same aging 00:21:23.010 --> 00:21:26.500 in the left and right side, so whatever differences there 00:21:26.500 --> 00:21:28.860 are between the left and the right, 00:21:28.860 --> 00:21:31.950 we attribute then to the blast from the rifle 00:21:31.950 --> 00:21:33.360 that the subject shot. 00:21:33.360 --> 00:21:36.740 So this cause of left right difference 00:21:36.740 --> 00:21:38.890 would be attributed to the high level sound. 00:21:45.210 --> 00:21:50.240 Here are some pictures from an experiment animal 00:21:50.240 --> 00:21:54.690 that has undergone a high sound level, or an overexposure. 00:21:56.020 --> 00:21:59.220 This is a normal-- I think, in this case, 00:21:59.220 --> 00:22:01.720 it's a Guinea pig cochlea. 00:22:01.720 --> 00:22:06.220 And you see the row of inner hair cells here. 00:22:06.220 --> 00:22:11.310 There is 1, 2, 3, 4, 5, about a dozen inner hair cells. 00:22:11.310 --> 00:22:13.410 That's just one row of inner hair cells. 00:22:13.410 --> 00:22:16.050 And then there are three rows of outer hair cells looking down 00:22:16.050 --> 00:22:17.591 onto the tops of the hair cells where 00:22:17.591 --> 00:22:19.670 you have the stereocilia sticking up at you. 00:22:21.440 --> 00:22:24.340 And there are 12 or 15 outer hair cells 00:22:24.340 --> 00:22:26.790 in each of rows 1, 2, and 3. 00:22:26.790 --> 00:22:31.430 And it's such a regular pattern, and they're all perfectly 00:22:31.430 --> 00:22:32.410 there. 00:22:32.410 --> 00:22:37.130 After listening to the overexposure of sound, 00:22:37.130 --> 00:22:39.425 there are quite a few inner hair cells lost. 00:22:40.940 --> 00:22:42.420 Those that are remaining sometimes 00:22:42.420 --> 00:22:44.460 have abnormal stereocilia. 00:22:46.000 --> 00:22:48.480 There are number of outer hair cells, in this case, 00:22:48.480 --> 00:22:50.400 in row one lost. 00:22:50.400 --> 00:22:53.400 And some that are remaining are indicated by these arrows 00:22:53.400 --> 00:22:55.055 to have abnormal stereocilia. 00:22:56.660 --> 00:22:59.490 And here's another example from a different place 00:22:59.490 --> 00:23:03.400 in the cochlea where almost the entire third row of outer hair 00:23:03.400 --> 00:23:08.390 cells is wiped out by the overexposure to noise. 00:23:10.080 --> 00:23:14.620 So what happens when you lose a hair cell? 00:23:14.620 --> 00:23:19.920 Well, the nearby supporting cells go fill in its space, 00:23:19.920 --> 00:23:22.130 and they take over. 00:23:22.130 --> 00:23:25.400 In mammals, such damage is permanent. 00:23:25.400 --> 00:23:27.825 Once the hair cell is killed, it never grows back. 00:23:29.220 --> 00:23:32.500 And there's a lot of interest in trying 00:23:32.500 --> 00:23:36.110 to coax the nearby supporting cells 00:23:36.110 --> 00:23:39.430 to, in these damage cochleas, become hair cells. 00:23:41.280 --> 00:23:44.190 But so far that has not been possible. 00:23:44.190 --> 00:23:47.400 The field was really excited about 20 years ago 00:23:47.400 --> 00:23:51.990 when this type of damage in a bird cochlea, 00:23:51.990 --> 00:23:55.780 if left for a month or so, you see 00:23:55.780 --> 00:23:58.300 reemerging small hair cells. 00:23:58.300 --> 00:24:01.350 And if you wait long enough, they become full hair cells. 00:24:01.350 --> 00:24:06.160 In the bird cochlea, the surrounding supporting cells, 00:24:06.160 --> 00:24:11.770 after damage to the hair cells, can then divide and become 00:24:11.770 --> 00:24:15.110 new hair cells, in the chicken cochlea, for example. 00:24:15.110 --> 00:24:18.470 And this was a serendipitous discovery 00:24:18.470 --> 00:24:23.545 where people were working on damaging chicken hair cells, 00:24:23.545 --> 00:24:27.140 and they were always waiting a couple days after the exposure 00:24:27.140 --> 00:24:29.450 to look at the cochleas. 00:24:29.450 --> 00:24:33.760 And there was a holiday vacation where they exposed the animals 00:24:33.760 --> 00:24:36.272 before, and they went out of town 00:24:36.272 --> 00:24:37.980 and came back three weeks later, and they 00:24:37.980 --> 00:24:41.340 found something must have gone wrong with the exposure 00:24:41.340 --> 00:24:42.890 because the hair cells are here. 00:24:42.890 --> 00:24:44.010 They're fine. 00:24:44.010 --> 00:24:45.940 But they figured out later that, actually, 00:24:45.940 --> 00:24:48.075 the supporting cells nearby had grown back. 00:24:49.600 --> 00:24:53.580 So that doesn't seem to help us in the mammalian pathway. 00:24:53.580 --> 00:24:56.690 There's some sort of growth factor or growth 00:24:56.690 --> 00:25:00.590 pathway in birds where these hair cells grow back, 00:25:00.590 --> 00:25:02.300 but not in the mammal unfortunately. 00:25:08.440 --> 00:25:13.150 So this is an example from a cochlea that's 00:25:13.150 --> 00:25:18.970 been treated by an aminoglycoside, 00:25:18.970 --> 00:25:22.330 and this is just to remind me to tell you 00:25:22.330 --> 00:25:29.090 that, once again, you can count hair cells along the cochlea. 00:25:29.090 --> 00:25:31.800 This is a plot of hair cells present 00:25:31.800 --> 00:25:34.350 where lots of black bars means lots of hair cells. 00:25:36.080 --> 00:25:40.690 And this is a beautiful example of this particular drug 00:25:40.690 --> 00:25:45.220 treatment, which I believe is kanamycin, 00:25:45.220 --> 00:25:48.850 and a certain dose doesn't affect the inner hair cells 00:25:48.850 --> 00:25:49.350 at all. 00:25:50.510 --> 00:25:52.410 But look at the outer hair cell loss 00:25:52.410 --> 00:25:56.640 in the basal part of the cochlea, virtually complete 00:25:56.640 --> 00:26:00.000 outer hair cell loss showing that the outer hair cells are 00:26:00.000 --> 00:26:04.341 more sensitive, they're more labile to this drug treatment 00:26:04.341 --> 00:26:05.590 than are the inner hair cells. 00:26:06.650 --> 00:26:12.220 And once again, the most vulnerable part of the cochlea 00:26:12.220 --> 00:26:13.760 is not the apex. 00:26:13.760 --> 00:26:17.080 0% distance from the apex is up here. 00:26:17.080 --> 00:26:18.870 And the basal region would be down here, 00:26:18.870 --> 00:26:20.990 and that's again the most vulnerable part 00:26:20.990 --> 00:26:22.380 of the cochlear for some reason. 00:26:25.060 --> 00:26:27.770 We can speculate about why this might 00:26:27.770 --> 00:26:29.950 be the case for drug treatment. 00:26:29.950 --> 00:26:32.970 We don't know this, but maybe the drug 00:26:32.970 --> 00:26:36.035 appears in more in a higher concentration 00:26:36.035 --> 00:26:37.410 in the basal part of the cochlea. 00:26:38.510 --> 00:26:41.900 In the cochlea, like you have in the brain, 00:26:41.900 --> 00:26:44.440 you have a blood-brain barrier. 00:26:44.440 --> 00:26:47.410 You have a blood-cochlea barrier. 00:26:47.410 --> 00:26:50.610 Obviously, some drug has gotten into the cochlea, 00:26:50.610 --> 00:26:53.970 but maybe the blood-cochlea barrier 00:26:53.970 --> 00:26:56.580 is more permeable down here in the base. 00:26:56.580 --> 00:26:59.080 And in the apex not as much drug got in. 00:26:59.080 --> 00:27:00.760 That's an idea. 00:27:00.760 --> 00:27:03.680 It hasn't been borne out by experimental evidence, 00:27:03.680 --> 00:27:06.620 but it's an idea that people have in mind. 00:27:06.620 --> 00:27:08.430 Or, it could be that the outer hair 00:27:08.430 --> 00:27:11.765 cells are just, for some reason, easier to kill in the base. 00:27:12.880 --> 00:27:17.050 That's more suggestive that all of these things 00:27:17.050 --> 00:27:19.760 affect the hair cells in the base more than the apex. 00:27:21.010 --> 00:27:26.560 Now, these were some of the original experiments that 00:27:26.560 --> 00:27:30.500 showed what outer hair cells did for us in the sense of hearing. 00:27:30.500 --> 00:27:33.940 So earlier in this course, we had the effect 00:27:33.940 --> 00:27:37.360 of knocking out the outer hair cells 00:27:37.360 --> 00:27:39.495 by knocking out the gene for Prestin. 00:27:41.350 --> 00:27:41.910 OK? 00:27:41.910 --> 00:27:44.040 In this case, the outer hair cells 00:27:44.040 --> 00:27:46.440 are knocked out by the drug treatment. 00:27:46.440 --> 00:27:49.120 So you've lesioned the outer hair cells 00:27:49.120 --> 00:27:50.820 in the very basal part of the cochlea. 00:27:51.710 --> 00:27:53.085 The inner hair cells are present. 00:27:54.830 --> 00:27:59.130 Let's look at the tuning curves from auditory nerve 00:27:59.130 --> 00:28:00.700 fibers in that preparation. 00:28:00.700 --> 00:28:05.350 Now let me remind you again what's happening here. 00:28:05.350 --> 00:28:10.260 So you have the inner hair cells, 00:28:10.260 --> 00:28:16.950 and you have the outer hair cells, 00:28:16.950 --> 00:28:21.200 which have been killed by the drug treatment. 00:28:21.200 --> 00:28:26.720 And then you have most of the auditory nerve fibers coming 00:28:26.720 --> 00:28:32.550 from the inner hair cells in the auditory nerve going 00:28:32.550 --> 00:28:33.860 to the brain. 00:28:33.860 --> 00:28:37.800 And the experiment then is to if you're recording electrodes, 00:28:37.800 --> 00:28:41.300 record from the auditory nerve fibers, 00:28:41.300 --> 00:28:46.510 get a single nerve fiber, and take its tuning curve. 00:28:46.510 --> 00:28:50.640 And that's what's shown on this top graph. 00:28:50.640 --> 00:28:54.950 So tuning curves from the normal region of the cochlea 00:28:54.950 --> 00:28:56.500 are normal shaped. 00:28:56.500 --> 00:29:00.266 They have sharp tips and tails, normal sensitivity. 00:29:02.197 --> 00:29:04.530 In the region of the cochlea when the drug treatment has 00:29:04.530 --> 00:29:07.870 lesioned the outer hair cells, the tuning curves 00:29:07.870 --> 00:29:09.650 look extremely abnormal. 00:29:09.650 --> 00:29:14.720 There's a tail, whatever tip there is is a tiny little tip, 00:29:14.720 --> 00:29:19.560 and there's a tremendous loss of sensitivity, as much as 60 00:29:19.560 --> 00:29:21.950 or more dB lost. 00:29:21.950 --> 00:29:24.540 Basically, these are tipless tuning curves. 00:29:26.030 --> 00:29:28.750 And now we know that the outer hair cells 00:29:28.750 --> 00:29:31.090 have their electromotility function. 00:29:31.090 --> 00:29:33.300 They are the cochlea amplifier. 00:29:33.300 --> 00:29:35.930 Without the amplifier, you lose the tip on the tuning curve. 00:29:37.410 --> 00:29:38.940 So that should be a mini review. 00:29:39.980 --> 00:29:42.630 This is the way the outer hair cells originally 00:29:42.630 --> 00:29:45.702 thought-- or discovered to be important 00:29:45.702 --> 00:29:47.160 in the sense of hearing, to provide 00:29:47.160 --> 00:29:50.050 the normal sensitivity and a sharp tuning. 00:29:50.050 --> 00:29:53.770 You can get all kinds of tuning curve abnormalities depending 00:29:53.770 --> 00:29:58.160 on whether you, in this case, lose all the outer hair cells. 00:29:58.160 --> 00:30:00.270 You cause disarray of the stereocilia. 00:30:01.750 --> 00:30:04.820 You have partial loss of the outer hair cells. 00:30:04.820 --> 00:30:09.650 All these kinds of things can be found after noise damage 00:30:09.650 --> 00:30:14.130 depending on the place of the cochlea you look at, 00:30:14.130 --> 00:30:18.250 the type of noise, the length of the noise exposure, 00:30:18.250 --> 00:30:19.940 and the animal. 00:30:19.940 --> 00:30:24.820 There's a lot of variability in noise damage from exposures 00:30:24.820 --> 00:30:27.020 to 10-- 10 different animals, you 00:30:27.020 --> 00:30:31.260 can have 10 different types of loss of hair cells. 00:30:31.260 --> 00:30:33.440 Noise damage is tremendously variable 00:30:33.440 --> 00:30:34.565 from subject to subject. 00:30:42.400 --> 00:30:45.390 Now, we also had-- this is another review. 00:30:45.390 --> 00:30:49.670 We also had the example of a psychophycial tuning curve. 00:30:49.670 --> 00:30:52.660 So this is a normal psychophysical tuning curve. 00:30:52.660 --> 00:30:56.670 Can somebody explain to me what the paradigm is? 00:30:57.940 --> 00:30:59.650 A psychophysical tuning curve, it's 00:30:59.650 --> 00:31:02.037 taken from a human listener, right? 00:31:02.037 --> 00:31:02.870 What's the paradigm? 00:31:10.490 --> 00:31:13.830 We had this in class, so we should all know what this is. 00:31:13.830 --> 00:31:17.825 A psychophysical tuning curve, you have a probe tone. 00:31:18.990 --> 00:31:21.030 I think that, in this case, the probe tone 00:31:21.030 --> 00:31:23.060 is right at the tip of the arrow. 00:31:23.060 --> 00:31:27.200 And the subject is instructed to listen to the probe tone 00:31:27.200 --> 00:31:30.070 and say when you hear the probe tone. 00:31:30.070 --> 00:31:31.520 Give the probe tone. 00:31:31.520 --> 00:31:33.270 Yes, I hear that definitely. 00:31:33.270 --> 00:31:33.880 Give it again. 00:31:33.880 --> 00:31:35.050 Oh, yes, I hear that. 00:31:35.050 --> 00:31:36.100 No problem. 00:31:36.100 --> 00:31:41.140 Then, you add a second tone, maybe a little bit higher 00:31:41.140 --> 00:31:43.922 in frequency than the probe tone. 00:31:43.922 --> 00:31:46.985 Probe tone was-- let's say, in this case, 1 kilohertz. 00:31:48.050 --> 00:31:54.730 The second tone, masker tone is 1.5 kilohertz, let's say. 00:31:54.730 --> 00:31:56.550 Introduce that. 00:31:56.550 --> 00:31:58.530 Person, yeah, I still hear the probe tone. 00:31:58.530 --> 00:31:59.977 I hear this other tone too. 00:31:59.977 --> 00:32:01.310 Oh, don't pay attention to that. 00:32:01.310 --> 00:32:02.680 Just listen to the probe tone. 00:32:02.680 --> 00:32:03.870 Sure, I hear that. 00:32:03.870 --> 00:32:06.700 Then, you boost the level of that second masker tone 00:32:06.700 --> 00:32:08.950 up to, in this case, 90 dB. 00:32:08.950 --> 00:32:12.089 The person says, I can't hear that probe tone anymore. 00:32:12.089 --> 00:32:12.880 Can you turn it up? 00:32:14.040 --> 00:32:16.110 And you plot that on your graph. 00:32:16.110 --> 00:32:16.920 That's a hit. 00:32:16.920 --> 00:32:18.180 That's a point. 00:32:18.180 --> 00:32:22.510 In that case, the masker has made inaudible the probe. 00:32:23.620 --> 00:32:26.200 And you go on varying your frequencies and levels 00:32:26.200 --> 00:32:30.165 until that masker masks the probe and the person 00:32:30.165 --> 00:32:31.870 says I can't hear the probe anymore. 00:32:31.870 --> 00:32:35.290 And you get the so-called psychophysical tuning curve, 00:32:35.290 --> 00:32:38.280 which has this very nice tip to it 00:32:38.280 --> 00:32:41.650 and a long low frequency tail from a normal hearing person. 00:32:43.110 --> 00:32:46.530 But a person with a sensorineural hearing loss 00:32:46.530 --> 00:32:49.450 often has a psychophysical tuning curve like this. 00:32:51.170 --> 00:32:53.260 This should remind you of the tuning curves 00:32:53.260 --> 00:32:55.760 that we just saw from auditory nerve fibers 00:32:55.760 --> 00:33:00.290 in the damaged cochlea, which is basically a tipless tuning 00:33:00.290 --> 00:33:00.790 curve. 00:33:02.150 --> 00:33:04.620 Perhaps in this case, the outer hair cells 00:33:04.620 --> 00:33:08.610 have been damaged by fun with sounds, 00:33:08.610 --> 00:33:11.990 and you have just the tail of the tuning curve. 00:33:13.260 --> 00:33:16.310 Now, here we come to the crux of why, 00:33:16.310 --> 00:33:19.090 in this person who has a sensorineural hearing 00:33:19.090 --> 00:33:22.040 loss-- they still have hearing, but they 00:33:22.040 --> 00:33:26.970 have a big loss-- why won't just a hearing aid work? 00:33:26.970 --> 00:33:29.330 You can certainly install a hearing aid 00:33:29.330 --> 00:33:33.980 into this person's ear canal and boost their threshold 00:33:33.980 --> 00:33:36.180 from what they used to here down at 0 00:33:36.180 --> 00:33:39.380 dB to what they now here at 60 dB 00:33:39.380 --> 00:33:41.750 You can amplify the sound at 60 dB. 00:33:41.750 --> 00:33:42.940 OK, fine. 00:33:42.940 --> 00:33:46.020 Then, they'll start to say, yeah, I here it no problem. 00:33:46.020 --> 00:33:49.770 What happens when this person goes to a crowded restaurant, 00:33:49.770 --> 00:33:52.030 and there's all this low frequency DIN? 00:33:53.510 --> 00:33:58.160 Well before, all the low frequency DIN was here. 00:33:58.160 --> 00:34:00.560 It didn't get into the response area 00:34:00.560 --> 00:34:03.880 of the sharply tuned tuning curve. 00:34:03.880 --> 00:34:06.700 Now, you have all this low frequencies 00:34:06.700 --> 00:34:09.790 that's amplified by the hearing aid. 00:34:09.790 --> 00:34:13.880 It now gets into the response area of the nerve fiber. 00:34:13.880 --> 00:34:15.980 That low frequency signal, which you 00:34:15.980 --> 00:34:18.469 don't want to pay attention to because you're listening 00:34:18.469 --> 00:34:23.150 at 1 kilohertz, is a competing, or masking, stimulus 00:34:23.150 --> 00:34:24.929 along with the signal. 00:34:24.929 --> 00:34:29.120 And so now, the person with the hearing aid and sensorineural 00:34:29.120 --> 00:34:31.840 hearing loss goes into the crowded restaurant 00:34:31.840 --> 00:34:35.580 and says I hear very well, but I can't understand the person 00:34:35.580 --> 00:34:37.830 across the table speaking to me. 00:34:37.830 --> 00:34:39.870 All I hear is this big noise. 00:34:39.870 --> 00:34:43.120 And no matter what I-- how I adjust my hearing aid, 00:34:43.120 --> 00:34:44.370 it just sounds noisy. 00:34:44.370 --> 00:34:46.020 I can't understand anymore. 00:34:46.020 --> 00:34:47.000 I can hear. 00:34:47.000 --> 00:34:50.810 They're certainly not deaf, but they can't understand anymore 00:34:50.810 --> 00:34:55.560 because before they had sharply tuned frequency tuning, 00:34:55.560 --> 00:34:57.995 and now they have no frequency tuning at all. 00:34:57.995 --> 00:34:59.080 It's very broad. 00:34:59.080 --> 00:35:02.230 That's the problem that a hearing aid 00:35:02.230 --> 00:35:06.590 can't deal with in terms of restoring normal hearing 00:35:06.590 --> 00:35:09.060 to a person with sensorineural hearing loss. 00:35:12.850 --> 00:35:14.860 Before I start to talk about implants, 00:35:14.860 --> 00:35:19.951 let me just remember to say what other processes affect 00:35:19.951 --> 00:35:20.450 our hearing. 00:35:21.650 --> 00:35:28.290 And we have a list just so I don't forget anything. 00:35:28.290 --> 00:35:38.540 And one of the important things is genetic causes. 00:35:41.190 --> 00:35:43.810 So maybe you can't see that from the back of the room, 00:35:43.810 --> 00:35:46.350 but number four here is genetic causes. 00:35:46.350 --> 00:35:49.390 There are babies who are born deaf, 00:35:49.390 --> 00:35:52.920 and in the state of Massachusetts, in most states, 00:35:52.920 --> 00:35:58.630 it's mandatory to test infant hearing at birth because you 00:35:58.630 --> 00:36:02.150 want to install a hearing aid or install a cochlea 00:36:02.150 --> 00:36:08.120 implant at a young age if the baby has hearing loss. 00:36:08.120 --> 00:36:13.810 And another cause that we should list 00:36:13.810 --> 00:36:17.585 are certain kinds of infections and disease processes. 00:36:20.540 --> 00:36:27.817 Number five, cause of hearing loss is diseases, for example, 00:36:27.817 --> 00:36:28.316 meningitis. 00:36:33.530 --> 00:36:35.270 And one of the MIT students that I 00:36:35.270 --> 00:36:38.760 used to use for demonstration of cochlea implant 00:36:38.760 --> 00:36:44.890 is deaf because at age 12, he got very sick with meningitis. 00:36:44.890 --> 00:36:50.550 And when I asked him, how did you go deaf? 00:36:50.550 --> 00:36:53.010 He said, well, I got sick with meningitis. 00:36:53.010 --> 00:36:59.290 And I was so sick that my MD's treated me with aminoglycosides 00:36:59.290 --> 00:37:02.080 so that they would kill the meningitis bacteria. 00:37:02.080 --> 00:37:06.240 And he isn't sure whether it's the meningitis or the side 00:37:06.240 --> 00:37:10.070 effect of the aminoglycosides that made him deaf. 00:37:10.070 --> 00:37:13.370 But when you woke up, he was cured, but he was deaf. 00:37:14.600 --> 00:37:20.580 So in some cases you're not sure which of these agents 00:37:20.580 --> 00:37:21.620 caused the hearing loss. 00:37:23.500 --> 00:37:25.590 So that's a pretty complete list now. 00:37:25.590 --> 00:37:29.570 Do we have any questions about what things cause hearing loss? 00:37:38.010 --> 00:37:42.050 And you might imagine that, during our lifetime, 00:37:42.050 --> 00:37:47.150 some of these things will be understood in a better way. 00:37:47.150 --> 00:37:50.940 It's clear why loud sound causes hearing loss. 00:37:50.940 --> 00:37:52.590 I mean the mechanical action. 00:37:52.590 --> 00:37:54.110 These things are moving. 00:37:54.110 --> 00:37:57.995 You could damage the very sensitive apparatus, 00:37:57.995 --> 00:37:58.870 like the stereocilia. 00:38:01.320 --> 00:38:04.250 Drugs, aminoglycosides bind to some 00:38:04.250 --> 00:38:06.280 of the membrane channels in hair cells. 00:38:07.430 --> 00:38:13.780 And maybe a therapy for this ototoxicity, this hearing loss 00:38:13.780 --> 00:38:15.890 created by these aminoglycosides, 00:38:15.890 --> 00:38:21.160 could be to install some competitive binder that 00:38:21.160 --> 00:38:24.210 would occupy the binding sites while you gave the drug 00:38:24.210 --> 00:38:24.710 therapy. 00:38:26.680 --> 00:38:30.750 We don't know at all what causes the hearing loss with aging. 00:38:30.750 --> 00:38:35.200 That's a very active subject in today's research. 00:38:35.200 --> 00:38:39.850 Genetic causes, same way, usually these 00:38:39.850 --> 00:38:44.370 are some sort of developmental factor or protein 00:38:44.370 --> 00:38:48.780 that's necessary for normal hair cell development and it's lost, 00:38:48.780 --> 00:38:52.260 in the case of recessive genetic problem. 00:38:54.080 --> 00:38:56.390 That's pretty clear how that arises. 00:38:56.390 --> 00:39:01.820 Meningitis, it's not clear how those diseases kill hair cells, 00:39:01.820 --> 00:39:02.810 but they certainly do. 00:39:04.340 --> 00:39:07.330 But there's certainly room to imagine 00:39:07.330 --> 00:39:11.330 that will be worked on quite actively in the next 10 00:39:11.330 --> 00:39:12.240 or 20 years. 00:39:12.240 --> 00:39:15.560 It's not known right now how the hair 00:39:15.560 --> 00:39:17.030 cells are lost in meningitis. 00:39:21.000 --> 00:39:28.460 So let's talk about, now, people who have complete hearing loss 00:39:28.460 --> 00:39:32.800 and are eligible for the so-called cochlear 00:39:32.800 --> 00:39:35.480 implants and other types of implants that restore hearing. 00:39:37.520 --> 00:39:41.790 So this is a nice slide from, I think, 00:39:41.790 --> 00:39:43.920 the paper that we're reading for today. 00:39:43.920 --> 00:39:46.690 And actually that reminds me, besides that paper, which 00:39:46.690 --> 00:39:50.020 is a very short one, easy to read, 00:39:50.020 --> 00:39:52.080 the textbook reading that I've assigned 00:39:52.080 --> 00:39:54.570 for today, which is most of chapter 00:39:54.570 --> 00:39:57.340 8 on auditory prostheses is excellent. 00:39:57.340 --> 00:39:59.160 It's really up to date. 00:39:59.160 --> 00:40:02.400 It tells you a lot about cochlear implants 00:40:02.400 --> 00:40:05.560 and coding for speech, which I probably 00:40:05.560 --> 00:40:06.870 won't have time to get into. 00:40:06.870 --> 00:40:10.660 But this is a really-- I mean hearing aids past and present, 00:40:10.660 --> 00:40:11.990 that's not so important. 00:40:11.990 --> 00:40:13.850 But it has a lot of good information 00:40:13.850 --> 00:40:17.300 on cochlear implants, so I'd encourage you definitely 00:40:17.300 --> 00:40:19.670 to read that textbook passage today. 00:40:20.900 --> 00:40:23.650 And the research report by Moore and Shannon 00:40:23.650 --> 00:40:28.030 is a very simple, easy to read paper. 00:40:28.030 --> 00:40:32.050 It shows you the sites where these various implants go. 00:40:32.050 --> 00:40:34.590 So the cochlear implant, obviously, 00:40:34.590 --> 00:40:38.010 is installed into the cochlea, right here. 00:40:39.990 --> 00:40:43.210 For people who have lost their hearing because of a problem 00:40:43.210 --> 00:40:47.360 with their auditory nerve, you put a cochlear implant in, 00:40:47.360 --> 00:40:49.700 and it's not going to do any good because the messages 00:40:49.700 --> 00:40:52.330 aren't going to be conveyed by the nerve into the brain. 00:40:53.780 --> 00:40:57.330 And so what's an example of someone like that? 00:40:57.330 --> 00:41:05.620 Well, a disease process called neurofibromatosis 00:41:05.620 --> 00:41:15.140 type two, or NF2, is a disease process where the subjects get 00:41:15.140 --> 00:41:18.500 tumors that grow on various nerves. 00:41:18.500 --> 00:41:23.250 And a very common type of tumor in NF2 patients 00:41:23.250 --> 00:41:28.700 is called a vestibular schwannoma. 00:41:31.710 --> 00:41:35.610 And a schwannoma is a tumor of the schwann cells 00:41:35.610 --> 00:41:39.210 that normally provide the myelin covering of peripheral nerves. 00:41:39.210 --> 00:41:41.290 And it grows on the vestibular branch 00:41:41.290 --> 00:41:43.120 of the eighth cranial nerve. 00:41:43.120 --> 00:41:46.270 Obviously, that's quite near the auditory branch 00:41:46.270 --> 00:41:48.110 of the eighth cranial nerve. 00:41:48.110 --> 00:41:49.990 And these tumors grow and grow. 00:41:49.990 --> 00:41:52.550 They probably rob the nerve of the blood supply. 00:41:52.550 --> 00:41:54.380 They probably put pressure on it, 00:41:54.380 --> 00:41:58.030 and they certainly infiltrate the tumor cells 00:41:58.030 --> 00:41:59.320 in amongst the fibers. 00:42:00.570 --> 00:42:04.740 And when the surgeon goes in to remove that type of tumor 00:42:04.740 --> 00:42:07.380 invariably the eighth cranial nerve is cut. 00:42:08.490 --> 00:42:13.040 So in that case, the subject has no nerve conveying messages 00:42:13.040 --> 00:42:14.640 from the cochlea into the brain. 00:42:15.990 --> 00:42:18.750 Well, the surgery is right here. 00:42:18.750 --> 00:42:20.370 You're removing a tumor from here, 00:42:20.370 --> 00:42:24.550 so it's fairly easy to go ahead and install an implant 00:42:24.550 --> 00:42:27.867 into the cochlear nucleus of the brain. 00:42:27.867 --> 00:42:29.200 The cochlear nucleus is visible. 00:42:30.500 --> 00:42:34.180 And that's what's called an auditory brainstem implant. 00:42:34.180 --> 00:42:36.460 It should be called a cochlear nucleus implant, 00:42:36.460 --> 00:42:37.418 but it's called an ABI. 00:42:38.720 --> 00:42:44.160 And an ABI-- I'm not going to talk too much about it-- 00:42:44.160 --> 00:42:48.400 but just suffice it to say, it's an array of surface electrodes. 00:42:49.580 --> 00:42:51.670 There are two companies making these. 00:42:51.670 --> 00:42:56.360 One has 15, and one has 21 in a checkerboard pattern. 00:42:58.920 --> 00:43:03.510 And the electrodes go onto the surface of the cochlear 00:43:03.510 --> 00:43:06.865 nucleus, and their placed there during the surgery. 00:43:08.620 --> 00:43:12.440 There was an experimental penetrating electrode array, 00:43:12.440 --> 00:43:15.310 or PABI, but that's been discontinued 00:43:15.310 --> 00:43:16.385 because of side effects. 00:43:18.150 --> 00:43:21.800 Some of these patients got trigeminal neuralgia, 00:43:21.800 --> 00:43:27.790 or pain sensations from nearby nerves, maybe by the fact 00:43:27.790 --> 00:43:30.075 that these electrodes penetrated into the brain. 00:43:31.350 --> 00:43:34.560 And so that underwent an FDA trial, 00:43:34.560 --> 00:43:35.826 but that's no longer used. 00:43:37.440 --> 00:43:42.010 But this surface ABI electrode is used in cases of NF2 00:43:42.010 --> 00:43:45.525 or in other cases where the nerve function is compromised. 00:43:47.780 --> 00:43:50.770 Those implants don't work very well. 00:43:50.770 --> 00:43:52.795 So if you look at this graph here. 00:43:53.800 --> 00:43:56.500 This is a graph of the different types of implants, 00:43:56.500 --> 00:43:58.830 especially I'll call your attention to the cochlear 00:43:58.830 --> 00:44:03.320 implant and the auditory brain stem implant. 00:44:03.320 --> 00:44:05.830 In the cochlear implant, you've got 00:44:05.830 --> 00:44:12.860 a lot of people who can-- if you do in a word recognition test, 00:44:12.860 --> 00:44:16.810 how often they get the words correct, a lot of them 00:44:16.810 --> 00:44:19.600 are placing at 100% of the words. 00:44:21.490 --> 00:44:25.490 So the task here is you stand behind the subject, 00:44:25.490 --> 00:44:27.620 or the audiologist stand behind the subject, 00:44:27.620 --> 00:44:31.410 and they say repeat after me, baby. 00:44:31.410 --> 00:44:32.745 And the person says baby. 00:44:35.130 --> 00:44:37.505 Sunshine, and the person says sunshine. 00:44:38.806 --> 00:44:41.370 And the person says, Red Socks. 00:44:41.370 --> 00:44:43.950 And you say, Cardinals. 00:44:43.950 --> 00:44:45.730 And they got one wrong. 00:44:48.770 --> 00:44:51.390 But anyway, you can do these tests 00:44:51.390 --> 00:44:54.090 without-- it's important to stand behind the person 00:44:54.090 --> 00:44:55.660 to make sure they're not lipreading. 00:44:55.660 --> 00:44:57.990 But a lot of cochlear implant users 00:44:57.990 --> 00:45:01.390 can get 100% on these tests. 00:45:01.390 --> 00:45:04.070 Now, the ABI, auditory brain stem implants, 00:45:04.070 --> 00:45:07.950 you've got many of the subject, if not all of them, 00:45:07.950 --> 00:45:12.750 saying the wrong word or not giving you any response here. 00:45:12.750 --> 00:45:14.870 So what good is the ABI? 00:45:16.800 --> 00:45:20.320 The real success story of these prostheses 00:45:20.320 --> 00:45:22.940 is that the person can understand speech. 00:45:22.940 --> 00:45:26.100 If the person can't understand speech, 00:45:26.100 --> 00:45:29.030 this thing isn't doing them too much good. 00:45:30.760 --> 00:45:34.290 So that's not to say that the ABI isn't 00:45:34.290 --> 00:45:36.700 successful in certain ways. 00:45:36.700 --> 00:45:40.815 The ABI is sometimes thought of as a lipreading assist device. 00:45:43.350 --> 00:45:46.900 So it helps these subjects read lips better. 00:45:46.900 --> 00:45:49.200 For example, if you guys are deaf 00:45:49.200 --> 00:45:52.530 and you look at my letters, and I make two different sounds, 00:45:52.530 --> 00:45:55.050 pa and ba. 00:45:55.050 --> 00:45:58.740 That looks exactly the same if you're trying to read my lips. 00:45:58.740 --> 00:46:00.485 But it sounds different to you. 00:46:00.485 --> 00:46:02.360 You guys have good hearing, and it 00:46:02.360 --> 00:46:05.840 may sound a little bit different to the ABI user, 00:46:05.840 --> 00:46:09.990 and it may give that ABI user a little bit of a step up 00:46:09.990 --> 00:46:14.405 and help versus someone who's just using lipreading. 00:46:17.590 --> 00:46:20.370 Now, just for completeness, I'll talk 00:46:20.370 --> 00:46:22.305 about the auditory midbrain implant. 00:46:25.340 --> 00:46:29.090 The idea here is to put the implant higher up 00:46:29.090 --> 00:46:29.970 in the pathway. 00:46:29.970 --> 00:46:31.230 Why would you want to do that? 00:46:32.340 --> 00:46:34.110 Well, some people think that the ABI 00:46:34.110 --> 00:46:37.000 doesn't work because there's been this tumor here. 00:46:38.180 --> 00:46:41.780 And surgeon has been hacking on the tumor to try to get it out, 00:46:41.780 --> 00:46:44.170 yanking and pulling on it. 00:46:44.170 --> 00:46:46.950 If the tumor didn't damage the cochlear nucleus, 00:46:46.950 --> 00:46:49.810 well, the hacking and tugging on it did. 00:46:51.060 --> 00:46:53.530 And so maybe you should put the implant 00:46:53.530 --> 00:46:56.420 further up where you haven't been 00:46:56.420 --> 00:46:58.120 hacking and everything's normal. 00:46:59.760 --> 00:47:02.864 And so that's the idea behind the auditory midbrain implant, 00:47:02.864 --> 00:47:04.530 which goes into the inferior colliculus. 00:47:06.010 --> 00:47:11.800 And there have been five patients 00:47:11.800 --> 00:47:13.920 who've gone undergone the auditory midbrain 00:47:13.920 --> 00:47:17.460 implant-- actually six, five very well documented. 00:47:18.850 --> 00:47:26.100 And the outcomes have been no better than the ABI, 00:47:26.100 --> 00:47:30.520 but that's because four out of the five well-documented 00:47:30.520 --> 00:47:32.335 didn't hit the right spot. 00:47:32.335 --> 00:47:35.340 The inferior colliculus is pretty small, 00:47:35.340 --> 00:47:38.720 and the part that you really want to go into 00:47:38.720 --> 00:47:41.365 is the tonotopically organized spot 00:47:41.365 --> 00:47:46.260 so that this needle electrode y-- 00:47:46.260 --> 00:47:49.760 this is a long electrode array with about 16 contacts 00:47:49.760 --> 00:47:51.810 on it, in this needle. 00:47:51.810 --> 00:47:55.890 And that's put into the tonotopic part of the IC, 00:47:55.890 --> 00:47:58.790 and it didn't get into the right place in most people. 00:47:58.790 --> 00:48:02.580 But even in the one individual, got it in the right place, 00:48:02.580 --> 00:48:04.185 it wasn't any better than the ABI. 00:48:05.520 --> 00:48:08.590 But there is going to be another clinical trial in which they 00:48:08.590 --> 00:48:10.950 implant five more subjects. 00:48:10.950 --> 00:48:13.880 And hopefully, the outcomes will be better on that. 00:48:16.630 --> 00:48:19.620 So that's the various types of electrodes. 00:48:19.620 --> 00:48:22.500 And, obviously, the cochlear implant 00:48:22.500 --> 00:48:23.650 is the real winner here. 00:48:24.700 --> 00:48:30.750 And we have been having readings-- Hi, Sheila-- we've 00:48:30.750 --> 00:48:32.550 been having readings in our class, 00:48:32.550 --> 00:48:35.160 and I'll do a reading now about the cochlear implant. 00:48:38.180 --> 00:48:41.880 This is from-- this is not made into a book form 00:48:41.880 --> 00:48:50.320 yet because this is from the esteemed academic publication 00:48:50.320 --> 00:48:54.055 called Yahoo Finance, on the web. 00:48:55.370 --> 00:49:03.770 And this is dated September 9, 2013. 00:49:03.770 --> 00:49:12.540 And the subject of this column is the Lasker Award. 00:49:24.150 --> 00:49:25.671 So the Lasker Award, does anybody 00:49:25.671 --> 00:49:26.920 know what the Lasker Award is? 00:49:26.920 --> 00:49:30.730 Sometimes, called the American Nobel Prize, 00:49:30.730 --> 00:49:32.360 so it's a very prestigious honor. 00:49:32.360 --> 00:49:35.670 It's given in several different fields, 00:49:35.670 --> 00:49:42.740 mostly in medicine and biomedical areas, 00:49:42.740 --> 00:49:45.160 and so there are sub-groups. 00:49:45.160 --> 00:49:47.800 And this one was given in clinical medical research 00:49:47.800 --> 00:49:48.780 award. 00:49:48.780 --> 00:49:55.010 So the 2013 Lasker Clinical Medical Research Award 00:49:55.010 --> 00:49:59.640 honors Graeme Clark, Ingeborg Hochmair and Blake Wilson 00:49:59.640 --> 00:50:04.380 for developing the modern cochlear implant, a device that 00:50:04.380 --> 00:50:07.770 bestows hearing on profoundly deaf people. 00:50:07.770 --> 00:50:09.520 The apparatus has, for the first time, 00:50:09.520 --> 00:50:12.570 substantially restored a human sense 00:50:12.570 --> 00:50:14.080 with a medical intervention. 00:50:15.620 --> 00:50:17.160 Blah, blah, blah. 00:50:17.160 --> 00:50:20.230 Throughout the world today, there are about 320,000 people 00:50:20.230 --> 00:50:22.330 outfitted with cochlear implants. 00:50:22.330 --> 00:50:25.680 Most recipients can talk on their cellphones 00:50:25.680 --> 00:50:29.835 and follow conversations in relatively quiet environments, 00:50:29.835 --> 00:50:31.740 and an increasing number of patients 00:50:31.740 --> 00:50:34.080 with severe age-related hearing loss 00:50:34.080 --> 00:50:36.950 are taking advantage of this marvelous invention. 00:50:36.950 --> 00:50:40.860 So the three people here, two of them 00:50:40.860 --> 00:50:45.320 are actually founders of cochlear implant companies. 00:50:45.320 --> 00:50:50.140 So you can think of Nobel Prizes and these prize being awarded 00:50:50.140 --> 00:50:51.900 to people who made big discoveries. 00:50:51.900 --> 00:50:56.020 And certainly, in the third case, Blake Wilson did. 00:50:56.020 --> 00:51:00.530 But in the first two, it's really conveying a technology 00:51:00.530 --> 00:51:04.460 to the masses that was recognized by this award. 00:51:04.460 --> 00:51:08.220 So that's the 2013 Lasker Award. 00:51:08.220 --> 00:51:13.010 So let's look a little bit about what a cochlear implant is, 00:51:13.010 --> 00:51:15.200 and that's shown in the next couple of slides. 00:51:15.200 --> 00:51:21.260 So the cochlear implant has an internal part, which 00:51:21.260 --> 00:51:25.310 is a series of electrodes that go into the cochlea, 00:51:25.310 --> 00:51:31.200 and the electrode comes out from here 00:51:31.200 --> 00:51:34.650 and goes into a so-called internal coil-- 00:51:34.650 --> 00:51:42.440 sorry about that-- and this is sometimes called the receiver 00:51:42.440 --> 00:51:45.190 because it gets messages from the external coil, 00:51:45.190 --> 00:51:49.050 or sometimes called the transmitter, across the skin 00:51:49.050 --> 00:51:49.560 here. 00:51:49.560 --> 00:51:53.485 So there's skin between the external and internal coils. 00:51:54.870 --> 00:51:57.130 On the outside, you have a microphone 00:51:57.130 --> 00:52:02.410 which picks up the sound and sends the microphone messages 00:52:02.410 --> 00:52:04.495 to a so-called speech processor. 00:52:05.640 --> 00:52:09.650 The speech processor sends transforms 00:52:09.650 --> 00:52:14.770 that sound wave form into a series of electrical pulses 00:52:14.770 --> 00:52:16.990 that are sent down the electrodes 00:52:16.990 --> 00:52:19.120 and stimulate the remaining auditory nerve 00:52:19.120 --> 00:52:20.820 fibers in the cochlea. 00:52:22.030 --> 00:52:26.070 So the cochlear implant has the electrodes, the internal part, 00:52:26.070 --> 00:52:28.210 the external part, and the speech processor 00:52:28.210 --> 00:52:29.325 and microphone. 00:52:31.410 --> 00:52:36.460 And I have a demonstration cochlear implant here. 00:52:36.460 --> 00:52:39.070 And I'm going to pass it around. 00:52:39.070 --> 00:52:43.330 These things are very valuable, so as demonstration models, 00:52:43.330 --> 00:52:44.680 they strip off the electrodes. 00:52:46.690 --> 00:52:48.550 So the part I'm passing around is just 00:52:48.550 --> 00:52:50.990 this tube that goes down here but not 00:52:50.990 --> 00:52:53.450 the electrodes themselves, and I think 00:52:53.450 --> 00:52:57.190 it has the internal and external coil, and obviously not 00:52:57.190 --> 00:52:59.140 the microphone or the speech processor, 00:52:59.140 --> 00:53:02.270 so just to give you an idea of the size. 00:53:02.270 --> 00:53:05.240 And I think this one, the tube comes down, 00:53:05.240 --> 00:53:08.680 and it coils around a little like the electrodes 00:53:08.680 --> 00:53:10.240 do as they coil in the cochlea. 00:53:13.250 --> 00:53:16.100 Now, this next slide is pretty important 00:53:16.100 --> 00:53:18.230 because it shows the electrodes coming 00:53:18.230 --> 00:53:20.410 into the cochlea in a cutaway diagram. 00:53:21.950 --> 00:53:25.790 And so the electrodes come in the basal turn of the cochlea. 00:53:25.790 --> 00:53:28.610 Remember there's an area in the bone that 00:53:28.610 --> 00:53:31.940 has a little membrane over it called the round window. 00:53:31.940 --> 00:53:35.280 Surgeons can go in there and make a tear in round window 00:53:35.280 --> 00:53:37.300 and put the implant in there. 00:53:37.300 --> 00:53:39.290 Or, they can drill a hole a little bit 00:53:39.290 --> 00:53:41.340 apical from the round window and start 00:53:41.340 --> 00:53:43.370 in the base of the cochlea, which 00:53:43.370 --> 00:53:47.700 is the big part of the cochlea and then 00:53:47.700 --> 00:53:53.180 thread just by pushing the electrode array more 00:53:53.180 --> 00:53:55.640 and more apical into the cochlea. 00:53:55.640 --> 00:54:00.475 Now, the cochlea gets pretty small as it goes very apically. 00:54:01.700 --> 00:54:07.020 And the electrodes don't fit into the apical region so far. 00:54:07.020 --> 00:54:10.210 So current cochlear implants only 00:54:10.210 --> 00:54:14.370 can be pushed in about to cover the basal half of the cochlea, 00:54:14.370 --> 00:54:15.320 the basal 50%. 00:54:18.100 --> 00:54:20.400 So that seems like a huge limitation. 00:54:20.400 --> 00:54:21.525 It's a bit of a limitation. 00:54:23.460 --> 00:54:25.710 Fortunately, it's not an extreme limitation 00:54:25.710 --> 00:54:30.350 because the spiral ganglion doesn't go all the way 00:54:30.350 --> 00:54:31.910 to the apical part of the cochlea. 00:54:31.910 --> 00:54:35.090 The ganglion is where the cell bodies of the auditory nerve 00:54:35.090 --> 00:54:36.090 is. 00:54:36.090 --> 00:54:40.790 And so there is ganglion that ends about 3/4 of the way out, 00:54:40.790 --> 00:54:43.090 so the last quarter wouldn't be helpful anyway. 00:54:45.330 --> 00:54:47.030 And here are the various electrodes 00:54:47.030 --> 00:54:49.370 along the cochlear implant. 00:54:49.370 --> 00:54:52.655 And modern cochlear implants have 22 electrodes. 00:54:57.710 --> 00:55:01.690 And they are hooked up. 00:55:01.690 --> 00:55:03.977 I'll show you how they're hooked up in just a minute. 00:55:03.977 --> 00:55:06.310 Actually, I'll show you how they're hooked up right now. 00:55:08.030 --> 00:55:12.940 The way this works is the microphone signal 00:55:12.940 --> 00:55:16.210 comes into the speech processor here, 00:55:16.210 --> 00:55:20.950 and the microphone signal is split up into various bands. 00:55:20.950 --> 00:55:24.160 The microphone might pick up only high frequency, 00:55:24.160 --> 00:55:27.170 in which case, this band would be active, 00:55:27.170 --> 00:55:29.920 or it might pick up middle frequencies, in which case 00:55:29.920 --> 00:55:34.180 these bands would be active, or it might pick up low frequency 00:55:34.180 --> 00:55:35.810 or it might pick up all frequencies. 00:55:36.860 --> 00:55:38.760 It depends on what the sound is. 00:55:40.060 --> 00:55:43.660 The output of those filters is sent to some processing 00:55:43.660 --> 00:55:49.240 schemes, which eventually result in little electric pulses, 00:55:49.240 --> 00:55:53.100 and those are shocks that are sent down 00:55:53.100 --> 00:55:55.740 into the cochlear implant electrodes. 00:55:55.740 --> 00:55:57.920 And this is supposed to be-- actually 00:55:57.920 --> 00:55:59.795 something's not happening here automatically. 00:56:01.320 --> 00:56:03.910 This is supposed to be electrode number one, which 00:56:03.910 --> 00:56:08.540 is the most apical electrode, and so on and so forth. 00:56:08.540 --> 00:56:12.030 And this scheme only ends in electrode 18, 00:56:12.030 --> 00:56:15.820 so this is an old diagram here because current cochlear 00:56:15.820 --> 00:56:16.670 implants have 22. 00:56:19.480 --> 00:56:23.320 So if you are hearing very low frequencies, 00:56:23.320 --> 00:56:26.005 you're going to be stimulating very apical electrodes. 00:56:27.430 --> 00:56:29.500 And if you're hearing the highest frequencies, 00:56:29.500 --> 00:56:31.680 you're going to stimulate the most basal electrode. 00:56:31.680 --> 00:56:35.250 And this is a recapitulation of the place code 00:56:35.250 --> 00:56:42.340 for sound frequency where base of the cochlear transduces 00:56:42.340 --> 00:56:45.940 in normal hearing, the high frequencies, and the apex 00:56:45.940 --> 00:56:47.310 transduces the low frequencies. 00:56:47.310 --> 00:56:49.850 So when we said the cochlear implant doesn't 00:56:49.850 --> 00:56:52.360 go all the way apically, it can't fit there. 00:56:52.360 --> 00:56:53.260 So what happens? 00:56:53.260 --> 00:56:55.540 Well, the apex isn't very well-stimulated 00:56:55.540 --> 00:56:56.740 in these designs. 00:56:58.470 --> 00:57:00.540 And so you will hear descriptions 00:57:00.540 --> 00:57:05.080 of people who have their implant turned on for the first time, 00:57:05.080 --> 00:57:07.210 and they'll say it sounds like Donald Duck. 00:57:07.210 --> 00:57:09.730 It sounds really shrill and very high-pitched. 00:57:10.900 --> 00:57:13.970 Well, a lot of the apex-- not drawn here-- is not stimulated. 00:57:15.730 --> 00:57:17.090 So what happens? 00:57:17.090 --> 00:57:19.490 So these people, after a month or two, 00:57:19.490 --> 00:57:22.040 say oh, yeah, it's sounding better and better. 00:57:23.820 --> 00:57:27.980 And so there's some sort of learning or plasticity 00:57:27.980 --> 00:57:30.090 that makes things settle down, and the voices 00:57:30.090 --> 00:57:33.260 sound a little bit more normal, maybe not normal, 00:57:33.260 --> 00:57:34.310 but more normal. 00:57:36.220 --> 00:57:39.510 And perfectly, as you saw from the graph before, 00:57:39.510 --> 00:57:42.710 normal word recognition scores can 00:57:42.710 --> 00:57:44.490 be achieved even though you're stimulating 00:57:44.490 --> 00:57:46.010 just a portion of the cochlea. 00:57:48.830 --> 00:57:54.330 Now, I have a movie here, and this gets on my nerves, 00:57:54.330 --> 00:57:56.400 but I want to show it to you because this 00:57:56.400 --> 00:57:58.610 is what's shown to patients who are 00:57:58.610 --> 00:57:59.990 about to get a cochlear implant. 00:58:01.240 --> 00:58:04.230 Gets on my nerves because you see hair cells in here that 00:58:04.230 --> 00:58:06.610 have stereocilia that are just waving around, 00:58:06.610 --> 00:58:08.575 but the stereocilia are really rigid. 00:58:10.077 --> 00:58:12.160 But anyway, I thought it would be interesting just 00:58:12.160 --> 00:58:19.380 to see what someone sees when they are getting 00:58:19.380 --> 00:58:22.500 this stuff from a cochlear implant. 00:58:22.500 --> 00:58:24.060 Let's see if this movie will play. 00:58:29.549 --> 00:58:33.042 [VIDEO PLAYBACK] In normal hearing, 00:58:33.042 --> 00:58:35.292 the hair in the inner ear-- 00:58:35.292 --> 00:58:36.250 PROFESSOR: I hate this. 00:58:39.290 --> 00:58:41.230 I mean the best membranes way over here. 00:58:41.230 --> 00:58:42.176 The hair cells-- 00:58:42.176 --> 00:58:44.160 -The hearing nerve still remains functional, 00:58:44.160 --> 00:58:48.128 but the hair cells have been lost or damaged. 00:58:48.128 --> 00:58:52.592 In a cochlear implant system, sound enters a microphone 00:58:52.592 --> 00:58:55.072 and travels to an external mini computer 00:58:55.072 --> 00:58:57.056 called a sound processor. 00:58:57.056 --> 00:58:59.040 The sound is processed and converted 00:58:59.040 --> 00:59:01.520 into digital information. 00:59:01.520 --> 00:59:04.992 This digital information is sent over a transmitter antenna 00:59:04.992 --> 00:59:07.472 to the surgically implanted part of the system. 00:59:08.960 --> 00:59:11.936 The implant will turn the sound information 00:59:11.936 --> 00:59:14.912 into electrical signals that travel down 00:59:14.912 --> 00:59:17.888 to an electrode array inserted into the tiny inner ear. 00:59:22.848 --> 00:59:25.824 The electrodes directly stimulate the auditory nerve, 00:59:25.824 --> 00:59:28.304 sending sound information to the brain. 00:59:30.288 --> 00:59:33.760 Bypassing the damaged inner ear, the cochlear implant 00:59:33.760 --> 00:59:37.232 provides an entirely new mechanism for hearing. 00:59:40.208 --> 00:59:41.430 [END VIDEO PLAYBACK] 00:59:41.430 --> 00:59:43.360 PROFESSOR: So that's what the patient's see. 00:59:44.690 --> 00:59:47.640 And how well does it work? 00:59:47.640 --> 00:59:51.490 So we can ask a demonstrator that we have today. 00:59:51.490 --> 00:59:54.540 Sheila come on up in front of the class. 00:59:54.540 --> 01:00:00.855 This is Sheila [? Zu ?], who is a MIT undergraduate. 01:00:02.410 --> 01:00:03.900 You're a senior now, right? 01:00:07.060 --> 01:00:09.625 What's your major at MIT? 01:00:09.625 --> 01:00:11.970 SHEILA: I'm the only in this major at MIT. 01:00:11.970 --> 01:00:14.330 I'm in [INAUDIBLE] technology and [? society ?] 01:00:14.330 --> 01:00:17.470 and [INAUDIBLE] is a joint major between Humanities 01:00:17.470 --> 01:00:18.220 and [? Chinese. ?] 01:00:18.892 --> 01:00:20.350 PROFESSOR: Are you an overachiever? 01:00:22.100 --> 01:00:23.025 SHEILA: I don't know. 01:00:23.025 --> 01:00:23.525 Maybe. 01:00:25.900 --> 01:00:28.260 PROFESSOR: So has anybody in the class 01:00:28.260 --> 01:00:31.035 ever spoken to a cochlear implant user before? 01:00:32.910 --> 01:00:34.380 SHEILA: I know some of them. 01:00:34.380 --> 01:00:36.184 PROFESSOR: You know some of these people? 01:00:36.184 --> 01:00:39.420 SHEILA: We're in the same dorm. [INAUDIBLE] in my sorority. 01:00:39.420 --> 01:00:39.920 OK. 01:00:39.920 --> 01:00:41.100 Great! 01:00:41.100 --> 01:00:45.530 So we can do this whatever way you want to. 01:00:45.530 --> 01:00:48.240 You can ask Sheila questions if you've already 01:00:48.240 --> 01:00:49.287 asked them to her. 01:00:49.287 --> 01:00:50.245 I'll ask her questions. 01:00:51.947 --> 01:00:53.280 Does anybody have any questions? 01:00:56.880 --> 01:00:57.380 Yes? 01:00:57.380 --> 01:00:59.640 AUDIENCE: How old were you when you got your implant? 01:01:00.990 --> 01:01:04.015 SHEILA: So I was born deaf, but I got implant 01:01:04.015 --> 01:01:05.500 when I was 3 years old. 01:01:07.280 --> 01:01:09.370 Actually, I got surgery when I was 2 years old. 01:01:09.370 --> 01:01:12.580 [INAUDIBLE] when I was 3 years old. 01:01:14.290 --> 01:01:16.210 PROFESSOR: So one question I often 01:01:16.210 --> 01:01:22.560 get about implants into children is how young can a child be 01:01:22.560 --> 01:01:24.660 and still be implanted successfully. 01:01:24.660 --> 01:01:27.520 So the surgeons at Mass Eye and Ear 01:01:27.520 --> 01:01:32.630 say that the cochlea is adult size by age 1 and 1/2, 01:01:32.630 --> 01:01:37.430 so typically, that's the age when a person who is born deaf 01:01:37.430 --> 01:01:39.570 is implanted these days, age 1 and 1/2. 01:01:39.570 --> 01:01:44.120 The idea to implant early is so that the subject 01:01:44.120 --> 01:01:47.000 can grow up and enjoy normal hearing, especially 01:01:47.000 --> 01:01:50.880 during a critical period for language formation, which 01:01:50.880 --> 01:01:54.680 was maybe starting at 1 and 1/2, 2 years old. 01:01:54.680 --> 01:01:57.680 So if you implant a person later, in their teens, 01:01:57.680 --> 01:02:01.122 and they haven't heard sound, they 01:02:01.122 --> 01:02:05.520 have a lot worse chances of acquiring normal language 01:02:05.520 --> 01:02:09.388 skills than someone like Sheila who has been implanted early. 01:02:09.388 --> 01:02:12.570 So the trend is to try to implant as early as possible. 01:02:14.546 --> 01:02:18.127 SHEILA: I want to point out that I may have been implanted when 01:02:18.127 --> 01:02:19.980 I was 3 years old, but I didn't start 01:02:19.980 --> 01:02:22.450 speaking until I was about 5 years old. 01:02:22.450 --> 01:02:24.920 And I didn't start learning math or learning 01:02:24.920 --> 01:02:27.250 how to read until I was 7 years old, so I was really 01:02:27.250 --> 01:02:28.516 delayed back then. 01:02:32.260 --> 01:02:34.070 PROFESSOR: Did you have a question? 01:02:34.070 --> 01:02:35.820 AUDIENCE: So I was just wondering, are you 01:02:35.820 --> 01:02:37.910 like reading my lips right now? 01:02:37.910 --> 01:02:39.070 SHEILA: Yes, I am. 01:02:39.070 --> 01:02:42.780 So the way it works, I have to see people's face, 01:02:42.780 --> 01:02:45.900 like how to read their lips, and I listen too at the same time. 01:02:46.940 --> 01:02:50.670 I could read your lips alone, but maybe not 100% accurate. 01:02:51.706 --> 01:02:54.270 Or, if I don't look at you lip, and listen to you, 01:02:54.270 --> 01:02:56.690 maybe not really understandable, so it's 01:02:56.690 --> 01:02:59.790 like I have to read lips and listen at the same time 01:02:59.790 --> 01:03:01.770 in order to understand you. 01:03:01.770 --> 01:03:06.570 PROFESSOR: But if you don't read lips, for example, 01:03:06.570 --> 01:03:09.220 in situations like talking on the telephone, 01:03:09.220 --> 01:03:11.270 can you understand someone on the telephone? 01:03:11.270 --> 01:03:13.445 SHEILA: It depends on the person. 01:03:13.445 --> 01:03:16.760 If I'm familiar with your voice, like I know my dad's voice. 01:03:16.760 --> 01:03:18.900 I can understand him pretty well, 01:03:18.900 --> 01:03:23.290 but if I'm talking to a stranger on the phone, then maybe not. 01:03:23.290 --> 01:03:25.955 And also, don't forget, there's a lot of background noises, 01:03:25.955 --> 01:03:28.968 so that makes it harder for me to hear people on the phone. 01:03:31.960 --> 01:03:36.440 PROFESSOR: When I-- let's say about 10 years ago in my lab, 01:03:36.440 --> 01:03:40.390 I hired a research assistant who used a cochlear implant, 01:03:40.390 --> 01:03:43.630 and she wanted me to shave off my mustache. 01:03:47.150 --> 01:03:49.880 It was because she had a little trouble reading 01:03:49.880 --> 01:03:52.070 my lips with my mustache. 01:03:52.070 --> 01:03:56.010 Now, my wife also has told me I should shave a mustache, 01:03:56.010 --> 01:03:57.243 but she has normal hearing. 01:04:00.624 --> 01:04:02.790 SHEILA: I actually had a professor at MIT 01:04:02.790 --> 01:04:06.000 when I was a freshman, I comment one day I 01:04:06.000 --> 01:04:07.820 had hard time understanding him because he 01:04:07.820 --> 01:04:08.736 had like a full beard. 01:04:09.534 --> 01:04:11.552 Then, next day, he shaved off everything. 01:04:11.552 --> 01:04:14.444 So he came up to me, I was like, who are you? 01:04:16.836 --> 01:04:17.336 [INAUDIBLE] 01:04:20.114 --> 01:04:21.280 PROFESSOR: That's very nice. 01:04:21.280 --> 01:04:22.170 Wow, interesting! 01:04:23.400 --> 01:04:27.360 I didn't shave off my mustache, neither for my assistant, 01:04:27.360 --> 01:04:28.612 nor for my wife. 01:04:28.612 --> 01:04:30.070 SHEILA: [INAUDIBLE] half is better. 01:04:31.412 --> 01:04:32.120 PROFESSOR: Maybe. 01:04:32.120 --> 01:04:32.620 Yeah. 01:04:34.280 --> 01:04:41.690 So if an audiologist were to test your speech comprehension, 01:04:41.690 --> 01:04:44.880 do you think you'd get every word correct 01:04:44.880 --> 01:04:46.440 or do you think you'd miss some? 01:04:47.500 --> 01:04:49.540 SHEILA: I think I probably miss some words 01:04:49.540 --> 01:04:52.600 or may not pronounce some words correctly, 01:04:52.600 --> 01:04:55.985 because the way I hear words may sound differently 01:04:55.985 --> 01:04:57.340 from what you hear. 01:04:57.340 --> 01:04:59.020 And sometimes, in English language, 01:04:59.020 --> 01:05:02.560 some words don't sound exactly the way it's written down. 01:05:03.800 --> 01:05:07.600 So I think my speech is not bad because, based 01:05:07.600 --> 01:05:09.942 on my interaction with people, they 01:05:09.942 --> 01:05:11.566 seem to understand me most of the time. 01:05:14.006 --> 01:05:14.982 Yeah? 01:05:14.982 --> 01:05:16.934 AUDIENCE: Do you know any other languages? 01:05:16.934 --> 01:05:19.362 SHEILA: I know another language. 01:05:19.362 --> 01:05:19.862 Yeah. 01:05:19.862 --> 01:05:21.920 I know a couple of languages. 01:05:21.920 --> 01:05:23.920 I know American sign language. 01:05:23.920 --> 01:05:26.880 I use it often to help, in some cases, 01:05:26.880 --> 01:05:29.040 when cochlear implant don't work. 01:05:29.040 --> 01:05:32.400 For example, if I'm in a loud bar or party 01:05:32.400 --> 01:05:34.977 and I can't hear people, but if I use sign language, 01:05:34.977 --> 01:05:35.810 I understand people. 01:05:37.120 --> 01:05:39.196 I know British sign language too, 01:05:39.196 --> 01:05:40.570 but that's another sign language. 01:05:42.600 --> 01:05:46.180 PROFESSOR: So you mentioned when you're in a party 01:05:46.180 --> 01:05:50.650 and you can't hear people, does that mean that there's 01:05:50.650 --> 01:05:55.490 a lot of noise that masks speakers and that's 01:05:55.490 --> 01:05:57.964 a hard situation for you? 01:05:57.964 --> 01:05:59.257 Right. 01:05:59.257 --> 01:06:00.715 SHEILA: So like the speaker's voice 01:06:00.715 --> 01:06:05.210 will blend into other speakers voices or background noises, 01:06:05.210 --> 01:06:08.255 so I tend to rely on lipreading or some other method 01:06:08.255 --> 01:06:08.880 to communicate. 01:06:11.442 --> 01:06:12.150 PROFESSOR: Right. 01:06:12.150 --> 01:06:16.820 So for example, in cochlear implants, 01:06:16.820 --> 01:06:21.920 a common problem is when there is an environment where 01:06:21.920 --> 01:06:25.420 there's many, many frequencies of sound, 01:06:25.420 --> 01:06:28.790 like a crowded restaurant or a party, 01:06:28.790 --> 01:06:32.780 and there's one speaker that you're trying to pay attention 01:06:32.780 --> 01:06:38.460 to and the subject gets overloaded 01:06:38.460 --> 01:06:40.560 on every single electrode. 01:06:40.560 --> 01:06:46.010 And so some kinds of cochlear implant processors 01:06:46.010 --> 01:06:50.680 try to circumvent that by trying to pick out in the spectrum 01:06:50.680 --> 01:06:53.420 the important peaks of the spectrum. 01:06:53.420 --> 01:06:55.810 So if you're listening to the vowel aa, 01:06:55.810 --> 01:06:57.220 you'd have three formants. 01:06:58.660 --> 01:07:02.720 The processor tries to pick out those formants and only 01:07:02.720 --> 01:07:07.490 present electrodes corresponding to those formants 01:07:07.490 --> 01:07:10.610 and turn all the other electrodes off so that there's 01:07:10.610 --> 01:07:14.055 a huge difference between where the formant is 01:07:14.055 --> 01:07:15.660 and where the nothing is. 01:07:15.660 --> 01:07:17.739 Really in theory, it's nothing, but actually, it 01:07:17.739 --> 01:07:18.905 could be a noisy background. 01:07:20.050 --> 01:07:24.250 So that is one kind of speech processor design. 01:07:24.250 --> 01:07:27.750 It's called the speech feature extractor, sometimes 01:07:27.750 --> 01:07:28.880 the speak chip. 01:07:28.880 --> 01:07:31.290 It's trying to pick out formants so 01:07:31.290 --> 01:07:33.460 that it can understand vowels. 01:07:33.460 --> 01:07:37.090 And it's supposed to be less sensitive to noise masking, 01:07:37.090 --> 01:07:39.635 which is a huge problem in cochlear implants. 01:07:40.726 --> 01:07:44.450 A cochlear implant user doesn't have the sharply tuned filter 01:07:44.450 --> 01:07:46.910 of the normal auditory nerve tuning 01:07:46.910 --> 01:07:50.400 curve that normal hearing people do. 01:07:50.400 --> 01:07:52.280 What about listening to music? 01:07:52.280 --> 01:07:54.419 Do you listen to music? 01:07:54.419 --> 01:07:54.960 SHEILA: Yeah. 01:07:54.960 --> 01:07:57.640 Like last month, I went to hear Yo-Yo Ma play. 01:07:57.640 --> 01:08:01.980 Like when-- I can hear music, but I'm not sure. 01:08:01.980 --> 01:08:04.680 I think I hear music differently from you guys 01:08:04.680 --> 01:08:06.856 because there's a whole range of frequencies, 01:08:06.856 --> 01:08:10.000 like you said, but yeah I can listen to music. 01:08:11.896 --> 01:08:14.266 AUDIENCE: How often do you go to the doctor for updates? 01:08:19.829 --> 01:08:21.670 SHEILA: How often do I go to-- 01:08:21.670 --> 01:08:22.700 AUDIENCE: You're doctor. 01:08:22.700 --> 01:08:24.075 SHEILA: Oh, you mean audiologist. 01:08:25.080 --> 01:08:29.045 I see audiologist like maybe once every year just 01:08:29.045 --> 01:08:31.630 for a checkup and remapping. 01:08:31.630 --> 01:08:34.970 PROFESSOR: So do you get a remapping 01:08:34.970 --> 01:08:36.979 or do they just bill your insurance company? 01:08:36.979 --> 01:08:37.520 SHEILA: Yeah. 01:08:39.763 --> 01:08:40.388 PROFESSOR: Yes. 01:08:40.388 --> 01:08:42.300 SHEILA: It's expensive. 01:08:42.300 --> 01:08:44.590 PROFESSOR: But do they-- do you know 01:08:44.590 --> 01:08:48.600 if they change the mapping for your electrodes? 01:08:48.600 --> 01:08:51.630 SHEILA: Yeah, they change it, but they told me 01:08:51.630 --> 01:08:54.084 it's not really a lot of changes. 01:08:54.084 --> 01:08:57.180 So I think the older you get, the less change 01:08:57.180 --> 01:08:58.901 is made than when you were younger. 01:08:58.901 --> 01:08:59.942 PROFESSOR: Perhaps, yeah. 01:09:01.170 --> 01:09:03.510 So that's interesting. 01:09:03.510 --> 01:09:06.100 So how do they do that mapping? 01:09:07.670 --> 01:09:13.410 Do they say here's electrode 1, and then here's electrode 2. 01:09:13.410 --> 01:09:14.819 Which is higher? 01:09:14.819 --> 01:09:15.700 Do they do that? 01:09:15.700 --> 01:09:19.029 SHEILA: Yeah, so I had to go into a special sound booth. 01:09:19.029 --> 01:09:22.949 So it's like a cell that is completely soundproof. 01:09:24.010 --> 01:09:26.840 And they will test me on a bunch of sounds 01:09:26.840 --> 01:09:29.229 like saying stop if it's too loud, 01:09:29.229 --> 01:09:32.340 or which one is louder or softer, 01:09:32.340 --> 01:09:34.920 can you repeat words after me, and so on. 01:09:34.920 --> 01:09:39.700 And they use all of that input to create a new map. 01:09:39.700 --> 01:09:40.870 PROFESSOR: Interesting. 01:09:40.870 --> 01:09:44.550 So apparently with cochlear implant users, 01:09:44.550 --> 01:09:46.450 the frequency mapping of the electrodes 01:09:46.450 --> 01:09:48.500 doesn't change in a big way. 01:09:48.500 --> 01:09:51.210 But in the auditory brain stem implant, 01:09:51.210 --> 01:09:55.410 they go through yearly checkups and, evidently, the mapping 01:09:55.410 --> 01:09:57.415 can change a great deal. 01:09:57.415 --> 01:09:59.400 So it's completely different. 01:09:59.400 --> 01:10:02.730 In cochlear implants, usually the most apical electrode 01:10:02.730 --> 01:10:05.900 evokes the lowest sensation of pitch 01:10:05.900 --> 01:10:09.301 and more basal electrodes get higher and higher sensations 01:10:09.301 --> 01:10:09.800 of pitch. 01:10:12.468 --> 01:10:14.509 AUDIENCE: How easy is it for you to differentiate 01:10:14.509 --> 01:10:15.982 between two voices? 01:10:15.982 --> 01:10:20.892 Like if you didn't see who was talking and if I said something 01:10:20.892 --> 01:10:22.856 and then Professor [? Brown ?] said something, 01:10:22.856 --> 01:10:25.802 how different would our voices sound to you? 01:10:25.802 --> 01:10:30.010 SHEILA: His voice is deeper, and you're farther away from me. 01:10:30.010 --> 01:10:34.540 So I think I can tell the difference between you two. 01:10:34.540 --> 01:10:37.630 I can tell difference between male and female voices. 01:10:39.052 --> 01:10:39.760 PROFESSOR: Right. 01:10:39.760 --> 01:10:41.920 Female voices sound higher usually. 01:10:41.920 --> 01:10:42.920 SHEILA: Higher pictched. 01:10:42.920 --> 01:10:43.420 Yeah. 01:10:45.434 --> 01:10:47.100 PROFESSOR: Do you know Mandarin Chinese? 01:10:48.535 --> 01:10:49.660 SHEILA: Yeah, a little bit. 01:10:49.660 --> 01:10:51.740 I can speak some Chinese, but not 01:10:51.740 --> 01:10:56.130 so good because I haven't used Chinese for a long time. 01:10:56.130 --> 01:10:58.564 PROFESSOR: It's a tonal language, right? 01:10:58.564 --> 01:10:59.105 SHEILA: Yeah. 01:10:59.105 --> 01:10:59.440 Oh my God! 01:10:59.440 --> 01:11:00.731 PROFESSOR: Does that give you-- 01:11:03.465 --> 01:11:06.810 SHEILA: It's like I went to China 4 years ago. 01:11:06.810 --> 01:11:08.310 I stayed in China for about a month. 01:11:08.310 --> 01:11:09.890 So my grandma, she couldn't speak 01:11:09.890 --> 01:11:11.895 English, so I had to speak to her in Chinese. 01:11:13.100 --> 01:11:16.820 But it's interesting how it's-- when I talk to people, 01:11:16.820 --> 01:11:20.440 like when I speak myself, I have to remember how use the tones, 01:11:20.440 --> 01:11:24.141 but if I listen to them, I can't tell the difference between 01:11:24.141 --> 01:11:24.640 tone. 01:11:24.640 --> 01:11:28.050 So what I do is I read their lips and listen. 01:11:28.050 --> 01:11:32.810 And I use context clues like so if the sound goes 01:11:32.810 --> 01:11:35.290 with this sound, so I think those 01:11:35.290 --> 01:11:37.945 sounds form a certain word. 01:11:37.945 --> 01:11:40.740 That's how I did, but I believe I 01:11:40.740 --> 01:11:43.750 can learn Chinese with a matter of practice 01:11:43.750 --> 01:11:45.050 and getting used to the sound. 01:11:46.762 --> 01:11:50.800 PROFESSOR: Apparently, cochlear implant users 01:11:50.800 --> 01:11:54.510 have a lot of problems with melodic intervals, 01:11:54.510 --> 01:11:58.110 octave matches, and tonal languages. 01:11:58.110 --> 01:12:02.360 The temporal code for frequency that 01:12:02.360 --> 01:12:05.370 helps us appreciate musical intervals 01:12:05.370 --> 01:12:08.670 is not present at all in any cochlear implant 01:12:08.670 --> 01:12:09.750 scheme that's used now. 01:12:11.130 --> 01:12:15.210 So you only have the place code for sound frequencies, 01:12:15.210 --> 01:12:18.990 you don't have the timing code in current generation cochlear 01:12:18.990 --> 01:12:19.820 implant users. 01:12:19.820 --> 01:12:22.970 And so the goal, remember, is to allow 01:12:22.970 --> 01:12:25.200 the users to understand speech. 01:12:25.200 --> 01:12:30.830 It's not in terms of recognizing musical intervals. 01:12:30.830 --> 01:12:35.910 Now, if cochlear implant companies were based in China, 01:12:35.910 --> 01:12:38.980 maybe the goal of understanding Mandarin Chinese, 01:12:38.980 --> 01:12:42.425 which is total, would be more important, but so far, 01:12:42.425 --> 01:12:43.300 that hasn't happened. 01:12:45.022 --> 01:12:46.438 AUDIENCE: Are you more comfortable 01:12:46.438 --> 01:12:49.896 with speaking with people or are you more comfortable 01:12:49.896 --> 01:12:52.370 with not speaking with people? 01:12:52.370 --> 01:12:54.430 SHEILA: Well, I'm more comfortable using 01:12:54.430 --> 01:12:57.750 sign language, but I don't mind going up in front of people 01:12:57.750 --> 01:12:58.460 and speaking. 01:13:04.360 --> 01:13:06.610 PROFESSOR: So one time, I had a demonstrator 01:13:06.610 --> 01:13:08.350 get asked this question. 01:13:08.350 --> 01:13:10.110 What's the stupidest thing you've ever 01:13:10.110 --> 01:13:11.640 done with your cochlear implant? 01:13:12.990 --> 01:13:15.510 And he had a response right away. 01:13:15.510 --> 01:13:19.490 He said when I first got my implant, I went to the beach. 01:13:19.490 --> 01:13:22.830 And I was 13 years old, and I was a typical teenager. 01:13:22.830 --> 01:13:25.615 And I saw someone else with a cochlear implant, 01:13:25.615 --> 01:13:26.990 and that was great because it was 01:13:26.990 --> 01:13:29.620 the first person I had ever seen. 01:13:29.620 --> 01:13:31.890 And so I said, let's swap processors. 01:13:33.860 --> 01:13:35.830 And that was actually a very stupid thing 01:13:35.830 --> 01:13:39.530 to do because each cochlear implant user is not 01:13:39.530 --> 01:13:43.290 only programmed for their coding for frequency, 01:13:43.290 --> 01:13:47.935 but they're coding for how much shock goes into auditory nerve. 01:13:49.200 --> 01:13:51.120 And some people who have electrodes 01:13:51.120 --> 01:13:54.770 close to the auditory nerve don't need much current all, 01:13:54.770 --> 01:13:58.060 but if your electrode is far away you need a lot of current. 01:13:58.060 --> 01:14:00.900 And this fellow got a processor that 01:14:00.900 --> 01:14:02.980 had been dialed in a lot of current, 01:14:02.980 --> 01:14:05.130 and so he got a big severe shock when 01:14:05.130 --> 01:14:08.380 you turn the other person's cochlear implant on. 01:14:08.380 --> 01:14:13.025 So that's something they tell you not to do, right? 01:14:15.320 --> 01:14:17.410 SHEILA: I don't think anybody told me that. 01:14:17.410 --> 01:14:20.320 But clearly I was like, OK, total wipe out. 01:14:20.320 --> 01:14:21.252 That's a bad shock. 01:14:21.252 --> 01:14:22.460 PROFESSOR: You did that also? 01:14:22.460 --> 01:14:23.832 SHEILA: Well, we both did. 01:14:23.832 --> 01:14:25.040 We exchange at the same time. 01:14:28.850 --> 01:14:31.450 PROFESSOR: Kids don't usually listen to adults, right? 01:14:34.600 --> 01:14:37.230 So are there a lot of students at MIT 01:14:37.230 --> 01:14:38.650 who use a cochlear implant? 01:14:40.336 --> 01:14:43.805 SHEILA: So far, by now, I think I'm the only one. 01:14:43.805 --> 01:14:47.210 But last year, there were two of us, but he graduated. 01:14:47.210 --> 01:14:48.950 So this year, I'm the only one. 01:14:48.950 --> 01:14:50.620 But I'm not the only deaf student. 01:14:50.620 --> 01:14:52.680 There are like two or three other deaf student, 01:14:52.680 --> 01:14:54.432 but they wear hearing aids. 01:14:57.700 --> 01:14:59.040 PROFESSOR: Question. 01:14:59.040 --> 01:15:01.200 AUDIENCE: How often do you turn it off-- 01:15:01.200 --> 01:15:03.420 or how often is it off? 01:15:03.420 --> 01:15:05.580 SHEILA: Oh, I turn it off every night. 01:15:05.580 --> 01:15:08.372 [INAUDIBLE] I go to bed because there's 01:15:08.372 --> 01:15:09.830 no point when I go to sleep, right? 01:15:11.141 --> 01:15:13.010 And when I take a shower or go swimming 01:15:13.010 --> 01:15:16.680 or if I want to have a [INAUDIBLE] day. 01:15:16.680 --> 01:15:18.970 On campus sometimes, I would get so tired 01:15:18.970 --> 01:15:22.079 of listening to people, I would just take it off. 01:15:24.450 --> 01:15:26.780 PROFESSOR: Which classes do you turn it on 01:15:26.780 --> 01:15:28.595 and which classes do you turn it off? 01:15:32.000 --> 01:15:32.500 That's OK. 01:15:34.940 --> 01:15:37.284 How long does your battery last? 01:15:37.284 --> 01:15:42.390 SHEILA: My battery last like 3 or 4 days, disposable battery, 01:15:42.390 --> 01:15:46.280 3 or 4 days, but rechargeable battery it's like one day. 01:15:49.280 --> 01:15:51.470 PROFESSOR: And do you have an implant 01:15:51.470 --> 01:15:54.450 on one side only, or both sides? 01:15:55.920 --> 01:15:58.370 SHEILA: In my right ear, it's just one side. 01:15:58.370 --> 01:16:01.300 PROFESSOR: Are you going to get it in the other ear? 01:16:01.300 --> 01:16:04.150 SHEILA: I'm not so sure because it takes time. 01:16:05.310 --> 01:16:09.480 I had to go through a surgery, to see doctors, and so 01:16:09.480 --> 01:16:12.570 on, so I'm not sure at that time because I'm so busy at MIT. 01:16:16.305 --> 01:16:19.275 AUDIENCE: What kind of alarm clock helps you to wake up? 01:16:24.740 --> 01:16:27.740 PROFESSOR: Do you have an alarm clock? 01:16:27.740 --> 01:16:28.740 SHEILA: Oh, yes. 01:16:28.740 --> 01:16:31.300 I have a special alarm clock. 01:16:31.300 --> 01:16:34.270 So I know you guys use a typical alarm. 01:16:34.270 --> 01:16:35.290 They make loud noises. 01:16:35.290 --> 01:16:40.760 But for me, I use alarm clock and a flashing lamp, 01:16:40.760 --> 01:16:44.785 so it just flash light on me that helps to wake me up. 01:16:44.785 --> 01:16:47.440 But some other people say it doesn't work for them, 01:16:47.440 --> 01:16:49.770 so what they do, they take a small vibrator thing 01:16:49.770 --> 01:16:52.200 and tuck it under their pillow or mattress, 01:16:52.200 --> 01:16:55.650 so it's like that then shocks them awake. 01:17:03.060 --> 01:17:04.990 PROFESSOR: What other kinds of problems 01:17:04.990 --> 01:17:07.895 do you have with your implant besides noise? 01:17:13.190 --> 01:17:15.946 SHEILA: I wish it was really waterproof because if I 01:17:15.946 --> 01:17:19.240 go swimming with my buddies who are not deaf, then 01:17:19.240 --> 01:17:20.500 how can I hear them. 01:17:21.580 --> 01:17:24.260 But right now, it's like a computer, 01:17:24.260 --> 01:17:26.730 so obviously, I can't just jump into water. 01:17:30.538 --> 01:17:33.673 AUDIENCE: I was going to ask who taught you sign language. 01:17:33.673 --> 01:17:35.298 SHEILA: Do you know some sign language? 01:17:35.298 --> 01:17:37.131 AUDIENCE: A little, but where did you learn? 01:17:39.080 --> 01:17:42.365 SHEILA: [INAUDIBLE] I learned when I was here at MIT. 01:17:43.406 --> 01:17:44.930 That was about like two years ago, 01:17:44.930 --> 01:17:47.622 so I took a class at Harvard. 01:17:47.622 --> 01:17:49.580 And then from there, I met a lot of deaf people 01:17:49.580 --> 01:17:53.190 here at MIT and outside of MIT, so I 01:17:53.190 --> 01:17:55.760 was able to be comfortable in sign language. 01:17:55.760 --> 01:17:56.450 I don't know. 01:17:56.450 --> 01:17:57.908 I guess it's not really hard for me 01:17:57.908 --> 01:17:59.660 to learn sign language compared to, 01:17:59.660 --> 01:18:03.090 let's say Spanish, because it's more official. 01:18:03.090 --> 01:18:04.970 You don't need to listen or speak, 01:18:04.970 --> 01:18:08.416 so it's really like all hands and [INAUDIBLE]. 01:18:08.416 --> 01:18:11.180 So it was pretty natural for me to pick it up. 01:18:12.980 --> 01:18:16.690 And I use sign language on a daily basis with my boyfriend 01:18:16.690 --> 01:18:21.490 or with my friends or whenever I ASL interpreter for my class. 01:18:23.460 --> 01:18:26.470 PROFESSOR: So you often have an ASL interpreter? 01:18:26.470 --> 01:18:29.580 SHEILA: Yeah, not all, but it depends on the class. 01:18:29.580 --> 01:18:34.030 For example, if the class is math or science lecture based, 01:18:34.030 --> 01:18:37.690 like one hour long lecture, then I use [INAUDIBLE] 01:18:37.690 --> 01:18:39.610 like real time closed captioning. 01:18:39.610 --> 01:18:42.690 Someone sit next to me, and on the computer screen, 01:18:42.690 --> 01:18:45.380 I read whatever professor saying in real time, 01:18:45.380 --> 01:18:46.880 and that person type out everything. 01:18:48.120 --> 01:18:52.930 Another class, like more of a lab or a hands on class 01:18:52.930 --> 01:18:55.980 or more moving around, then I use ASL interpreter 01:18:55.980 --> 01:18:59.248 because it's just awkward to carry around a laptop reading 01:18:59.248 --> 01:19:00.224 words on a screen. 01:19:06.742 --> 01:19:08.950 PROFESSOR: What do you want to do after you graduate? 01:19:10.676 --> 01:19:12.800 SHEILA: Right now, I'm applying to one Ph.d program 01:19:12.800 --> 01:19:15.730 at Harvard that's a program he is a part of, 01:19:15.730 --> 01:19:19.750 so he may be my professor next year even. 01:19:19.750 --> 01:19:20.690 PROFESSOR: Yeah. 01:19:20.690 --> 01:19:21.420 If you graduate. 01:19:28.910 --> 01:19:30.150 What's the program? 01:19:30.150 --> 01:19:31.630 This is a little sales pitch. 01:19:31.630 --> 01:19:33.031 You can tell them about it. 01:19:34.432 --> 01:19:36.460 SHEILA: The program is part of Harvard, 01:19:36.460 --> 01:19:38.820 but it was a part of MIT before. 01:19:38.820 --> 01:19:43.010 But it's a Ph.d program called Speech and Hearing 01:19:43.010 --> 01:19:44.660 Bioscience and Technology. 01:19:44.660 --> 01:19:45.202 Right? 01:19:45.202 --> 01:19:45.910 PROFESSOR: Right. 01:19:45.910 --> 01:19:48.890 SHEILA: And it's a program that focus on hearing, cochlear 01:19:48.890 --> 01:19:50.880 implant, hearing aids, or anything 01:19:50.880 --> 01:19:52.530 related to hearing and speech. 01:19:54.018 --> 01:19:56.120 So right now, I'm applying to that program. 01:19:56.120 --> 01:19:58.400 We'll see how it goes. 01:19:58.400 --> 01:19:59.066 PROFESSOR: Good. 01:20:02.503 --> 01:20:05.449 AUDIENCE: This is personal, but did your boyfriend already 01:20:05.449 --> 01:20:06.930 know sign language? 01:20:06.930 --> 01:20:09.415 SHEILA: Oh, he's deaf himself, so he knows sign language. 01:20:09.415 --> 01:20:10.180 But he's like me. 01:20:10.180 --> 01:20:12.200 He could speak and sign. 01:20:12.200 --> 01:20:13.705 But difference is he had cochlear-- 01:20:13.705 --> 01:20:16.387 no wait-- he had hearing aid, I have cochlear implant. 01:20:20.379 --> 01:20:25.369 AUDIENCE: Do you think that you've become a faster reader? 01:20:25.369 --> 01:20:27.864 Like do you think you're faster at reading than most people 01:20:27.864 --> 01:20:29.860 because you rely on it more? 01:20:29.860 --> 01:20:31.356 SHEILA: I would be more what? 01:20:31.356 --> 01:20:31.856 Faster? 01:20:31.856 --> 01:20:33.022 AUDIENCE: Faster at reading. 01:20:33.022 --> 01:20:34.850 SHEILA: Faster at reading lips? 01:20:34.850 --> 01:20:38.343 AUDIENCE: Like reading words on a screen or reading text. 01:20:39.370 --> 01:20:40.790 SHEILA: That's a good question. 01:20:40.790 --> 01:20:42.590 I never thought of that. 01:20:42.590 --> 01:20:45.245 It's a possibility because yeah, you're right. 01:20:45.245 --> 01:20:47.469 Have you seen it in person? 01:20:47.469 --> 01:20:48.635 AUDIENCE: I haven't seen it. 01:20:48.635 --> 01:20:49.801 SHEILA: You haven't seen it. 01:20:49.801 --> 01:20:51.610 So it's like on that comp screen, 01:20:51.610 --> 01:20:53.660 where she type out words really fast. 01:20:53.660 --> 01:20:55.520 So I have to read fast. 01:20:55.520 --> 01:20:58.170 But after one hour, I got too tired to read, 01:20:58.170 --> 01:21:00.370 so I just look around the room. 01:21:03.250 --> 01:21:06.130 The good thing is after class, she send me a transcript, 01:21:06.130 --> 01:21:07.755 so I will go back and look at it again. 01:21:08.970 --> 01:21:11.805 So I mean, it's really tiring to look at computer screen, 01:21:11.805 --> 01:21:14.593 for one hour straight, reading words really quickly. 01:21:20.887 --> 01:21:21.470 PROFESSOR: OK. 01:21:21.470 --> 01:21:23.500 So the cochlear implant is sometimes 01:21:23.500 --> 01:21:27.350 called the most successful neural prosthesis, 01:21:27.350 --> 01:21:28.980 and here we have an example. 01:21:31.230 --> 01:21:33.718 So let's give Sheila a hand. 01:21:33.718 --> 01:21:35.710 Thank you very much for coming. 01:21:37.710 --> 01:21:40.445 And we'll talk next time about brain stem reflexes. 01:21:40.445 --> 01:21:44.540 So we'll hang around if you have any other questions.