1. Cochlear Implants STATS 19 SEM 2. 263057202. Talk 8. A.L. Yuille. Dept. Statistics. yuille@stat.ucla.edu

2. Nerve Cells and the Brain: The brain is made up of two types of cells. The brain is made up of two types of cells. Neurons and Glial Cells. Neurons and Glial Cells. Neurons are the basic elements of the nervous system. Information travels along them by electric impluses. Neurons are the basic elements of the nervous system. Information travels along them by electric impluses. Neurons transmit to other neurons by synapses. Neurons transmit to other neurons by synapses. Glial cells play a supporting role. Maintain brain structure. Do not conduct electricity. Glial cells play a supporting role. Maintain brain structure. Do not conduct electricity.

3. Nerve Cells and the Brain. Neurons and Networks of Neurons. Neurons and Networks of Neurons. Brain has 100,000,000,000 neurons. Brain has 100,000,000,000 neurons. Each communicates with several 1,000 other neurons. Each communicates with several 1,000 other neurons.

4. Nerve Cells and the Brain Number of nerve cells 100,000,000,000 is about the number of trees in the Amazon rainforest. Number of nerve cells 100,000,000,000 is about the number of trees in the Amazon rainforest. Number of nerve cell connections 1,000,000,000,000,000 is about the number of leaves in rainforest. Number of nerve cell connections 1,000,000,000,000,000 is about the number of leaves in rainforest. Number of connections in the world’s telephone system (biggest machine on the planet). Number of connections in the world’s telephone system (biggest machine on the planet). Brain is the most complicated system in the Universe. Brain is the most complicated system in the Universe.

5. Magnetic Resonance Imaging (MRI) MRI can get 3D pictures of organs in the brain – by placing patient in a huge magnet. MRI can get 3D pictures of organs in the brain – by placing patient in a huge magnet. Hydrogen atoms (2/3 body) absorb and give off magnetic energy. Hydrogen atoms (2/3 body) absorb and give off magnetic energy. Calculate images from variations in how this magnetic energy is absorbed and emitted in the body. Calculate images from variations in how this magnetic energy is absorbed and emitted in the body. Low energy, non-invasive. Low energy, non-invasive.

6. Functional Magentic Resonance Imaging (fMRI). Use fMRI to measure blood flow in the brain. Use fMRI to measure blood flow in the brain. Active areas require more blood. fMRI can measure the oxygen content of the blood. Active areas require more blood. fMRI can measure the oxygen content of the blood. Molecules in the blood cells respond differently to the magnetic field depending on how much oxygen they are carrying. Molecules in the blood cells respond differently to the magnetic field depending on how much oxygen they are carrying.

7. Language and the Brain. Moghul Emperor Akbar Khan (17 th century). Moghul Emperor Akbar Khan (17 th century). Put 12 babies with dumb nurses in a castle. Put 12 babies with dumb nurses in a castle. At age 12, brought them to his palace – and found they did not speak any language at all. At age 12, brought them to his palace – and found they did not speak any language at all.

8. Language and Grammar Linguistics: rules of syntax (grammar) operate independent of meaning (semantics). Linguistics: rules of syntax (grammar) operate independent of meaning (semantics). Chomsky’s claim: people have an innate, universal, system of syntax which makes laws governing elementary sentences. Chomsky’s claim: people have an innate, universal, system of syntax which makes laws governing elementary sentences. “Colourful green ideas sleep furiously” – grammatical, but not meaningful. “Colourful green ideas sleep furiously” – grammatical, but not meaningful.

9. Language and the Brain Left-hemisphere dominant for language. (strongest for right-handed males). Left-hemisphere dominant for language. (strongest for right-handed males). Broca’s area. Identified in 1861. Damage to area impairs speech production. Broca’s area. Identified in 1861. Damage to area impairs speech production. Speech production: but also involves some speech comprehension. (Syntactic?) Speech production: but also involves some speech comprehension. (Syntactic?) Wernicke’s area. Identified 1873. Damage to it affects speech comprehension. Wernicke’s area. Identified 1873. Damage to it affects speech comprehension. But also production. (Semantic?) But also production. (Semantic?)

10. Cochlear Implants. The Most Successful Implant Device. The Most Successful Implant Device. Provides good artificial input to the auditory system, but does not solve the Cortical Part of Language. Provides good artificial input to the auditory system, but does not solve the Cortical Part of Language. A pre-linguistically deafened child or adult find it very hard to use them. A pre-linguistically deafened child or adult find it very hard to use them. First six years are crucial to language acquisition and usage. First six years are crucial to language acquisition and usage.

11. Cochlear Implants Can probably train completely deaf humans to hear, provided it is done early. Can probably train completely deaf humans to hear, provided it is done early. Experiments on kittens than are born deaf. Experiments on kittens than are born deaf. Implants given at age 3-4 months. Implants given at age 3-4 months. Several months of training, kittens behaviour showed they “hear” sounds normally. (Brain activity confirms this). Several months of training, kittens behaviour showed they “hear” sounds normally. (Brain activity confirms this).

12. Cochlear Implants 500,000 Americans have severe hearing loss. 500,000 Americans have severe hearing loss. 32,000 people world wide would implants. Cost $30-50,000. 32,000 people world wide would implants. Cost $30-50,000. Most common hearing loss (85%) is caused by damage to cochlear hair cells in the inner ear. Most common hearing loss (85%) is caused by damage to cochlear hair cells in the inner ear. Damage cn be genetic, or caused by disease (measles, meningitis, injury, aging, drugs). Damage cn be genetic, or caused by disease (measles, meningitis, injury, aging, drugs). For adults, implants can be miraculous. 10 seconds like pinball. In two minutes, could hear and have conversations. For adults, implants can be miraculous. 10 seconds like pinball. In two minutes, could hear and have conversations.

13. Cochlear Implants. Tiny microphone attached near the ear. Implants send sounds through a processor, back to a transmitter, that delivers the sound through electrodes, stimulating the auditory nerve. Tiny microphone attached near the ear. Implants send sounds through a processor, back to a transmitter, that delivers the sound through electrodes, stimulating the auditory nerve. 40,000 Americans are deaf-blind. They seem to benefit from Cochlear implants. 40,000 Americans are deaf-blind. They seem to benefit from Cochlear implants.

14. Cochlear. Recipients of Cochlear implants suggest Recipients of Cochlear implants suggest a true hearing percept (i.e. not like having to guess what the sound means). Awareness of sound in the environment. Awareness of sound in the environment. Can combine with lip reading, or be used independently. Can combine with lip reading, or be used independently. Typically understand 60% speech within two weeks, 80% within a few months (sufficient for telephone use). Typically understand 60% speech within two weeks, 80% within a few months (sufficient for telephone use).

15. Cochlear Implant. Takes over the operation of the Cochlear – not just a hearing-aid (amplifier). Takes over the operation of the Cochlear – not just a hearing-aid (amplifier). Damaged hair cells can cause damage of adjacent auditory neurons (very bad). Damaged hair cells can cause damage of adjacent auditory neurons (very bad). But usually auditory neurons remain. But usually auditory neurons remain.

16. Auditory System. Cochlear nerves from ears transmit acoustic signals to cochlear nucleus in lower brainstem. Cochlear nerves from ears transmit acoustic signals to cochlear nucleus in lower brainstem. Then proceed to temporal lobes of the cerebral cortex. Then proceed to temporal lobes of the cerebral cortex.

17. Cochlear and the Ear Outer Ear – Middle Ear – Inner Ear. Outer Ear – Middle Ear – Inner Ear. Outer Ear picks up acoustic pressure waves. Outer Ear picks up acoustic pressure waves. Converts them into mechanical vibrations by a series of small bones in middle ear. Converts them into mechanical vibrations by a series of small bones in middle ear. In Inner Ear, the Cochlear (snail shaped cavity full of fluid) transforms them into fluid vibrations. In Inner Ear, the Cochlear (snail shaped cavity full of fluid) transforms them into fluid vibrations.

18. Cochlear and the Ear Pressure variations within the fluid of the Cochlear lead to displacement of the basilar membrane. Pressure variations within the fluid of the Cochlear lead to displacement of the basilar membrane. The displacements contain information about the frequency of the acoustic signal. The displacements contain information about the frequency of the acoustic signal. There are hair cells attached to the basilar membrane. There are hair cells attached to the basilar membrane. Bending of hair cells releases electrochemical substance which causes auditory neurons to fire. Bending of hair cells releases electrochemical substance which causes auditory neurons to fire. Signals presence of excitation at a particular site Signals presence of excitation at a particular site

19. Auditory Fequencies Sound can be decomposed in frequency components. Sound can be decomposed in frequency components. Different frequency components cause maximum vibration at different points along the basilar membrane. Different frequency components cause maximum vibration at different points along the basilar membrane. Low frequencies cause biggest amplitudes at the apex of basilar membrane (fig 3). Low frequencies cause biggest amplitudes at the apex of basilar membrane (fig 3). High frequencies near the base (stapes). High frequencies near the base (stapes).

20. Audio.

21. Audio.

22. Auditory Frequences. Cochlear implant must activate a range of frequencies. Cochlear implant must activate a range of frequencies. Signal processor in implant must decompose the auditory signal into frequencies (Fourier Analysis). Signal processor in implant must decompose the auditory signal into frequencies (Fourier Analysis). Activate places in the Cochlear by electrodes to correspond to input frequencies. Activate places in the Cochlear by electrodes to correspond to input frequencies. Loudness depends on how many auditory neurons are activated. Increase strength of electric current. Loudness depends on how many auditory neurons are activated. Increase strength of electric current.

23. Cochlear Implants Electrode arrays inserted in the scala tympani to depths of 22-30 mm. Electrode arrays inserted in the scala tympani to depths of 22-30 mm. Often 22 electrodes are used (frequency channels). Often 22 electrodes are used (frequency channels). First devices used a single electrode, was not ideal. First devices used a single electrode, was not ideal.

24. Cochlear Implants Transmission to implant. Transmission to implant. Transcutaneous. Radio frequency link. Transmitter and implanted receiver held in place by a magnet. Transcutaneous. Radio frequency link. Transmitter and implanted receiver held in place by a magnet. Percutaneous. Transmits to electrodes by plug connections. Percutaneous. Transmits to electrodes by plug connections.

25. Performance Before – sentence recognition 30% or less. Before – sentence recognition 30% or less. After – aim between 70% to 100%. Patients can often fill in missing words by context. After – aim between 70% to 100%. Patients can often fill in missing words by context.

26. Children Implant will help child: Implant will help child: (1) Produce speech (feedback). (1) Produce speech (feedback). (2) Understand speech. (2) Understand speech. Implants give steady improvement for both skills. (Up to four years). Implants give steady improvement for both skills. (Up to four years). The earlier the better. The earlier the better. Fastest improvement for postlingually deafened children. Fastest improvement for postlingually deafened children.

27. Factors affecting performance Duration of Deafness – the shorter the better. Duration of Deafness – the shorter the better. Age of onset of deafness – better if postlingual. Age of onset of deafness – better if postlingual. Age at implantation – Best to implant prelingual children early (2 years min). Age at implantation – Best to implant prelingual children early (2 years min).

28. Cochlear History. Pythagoras – sound is an oscillation of the air. (6 th century BC). Pythagoras – sound is an oscillation of the air. (6 th century BC). Fallopio (1561) discover the Cochlear. Fallopio (1561) discover the Cochlear. Cochlear Figure. Cochlear Figure. Corti (1851) found hair cells on the organ of Corti. Corti (1851) found hair cells on the organ of Corti. Helmholtz suggested that the organ of Corti vibrates in response to different sound frequencies. Helmholtz suggested that the organ of Corti vibrates in response to different sound frequencies.

29. Cochlear History Von Bekesy (Nobel Prize 1961) showed that vibrations of the Cochlear did correspond to sound waves. Von Bekesy (Nobel Prize 1961) showed that vibrations of the Cochlear did correspond to sound waves. Different parts of the Organ of Corti were sensitive to different tones. Different parts of the Organ of Corti were sensitive to different tones. Zwicker (1957) showed that the auditory system organized sounds into 24 channels. 30,000 nerve fibers. Zwicker (1957) showed that the auditory system organized sounds into 24 channels. 30,000 nerve fibers.

30. Hearing Loss Two types of hearing loss. Two types of hearing loss. (I) Conductive Hearing Loss: Damage to the apparatus that transmits sound to the Cochlea (e.g. eardrum). Can be treated by hearing aids or surgery to raise volume. (I) Conductive Hearing Loss: Damage to the apparatus that transmits sound to the Cochlea (e.g. eardrum). Can be treated by hearing aids or surgery to raise volume. (II) Sorineural: Destruction of the hair cells within the organ of Corti. (II) Sorineural: Destruction of the hair cells within the organ of Corti.

31. Hearing Loss How many electrodes needed? 30,000 for all the nerve fibers? 24 for Zwicker’s channels? 6 based on frequency analysis? How many electrodes needed? 30,000 for all the nerve fibers? 24 for Zwicker’s channels? 6 based on frequency analysis? Kiang (1965) discovered that an entire population of nerve fibers must be used to transmit a single frequency of sound (single fibers can produce impluses at most 300 times per second, but speech involves frequencies up to 4,000 cycles per second). Kiang (1965) discovered that an entire population of nerve fibers must be used to transmit a single frequency of sound (single fibers can produce impluses at most 300 times per second, but speech involves frequencies up to 4,000 cycles per second).

32. Newer Discoveries New discoveries keep suggesting ways to improve Cochlear Implants. New discoveries keep suggesting ways to improve Cochlear Implants. Better understanding of how the nerve fibers encode the speech frequencies. Better understanding of how the nerve fibers encode the speech frequencies. Understanding the temporal pattern of the nerve fibers. Understanding the temporal pattern of the nerve fibers. Detailed understanding of how the hair cells change sound into electrical nerve impulses (2002). Detailed understanding of how the hair cells change sound into electrical nerve impulses (2002).

33. Speech versus Vision Speech input is simpler than Vision input. Speech input is simpler than Vision input. Acoustic signals can be decomposed in terms of frequencies. 30,000 hair cells. Acoustic signals can be decomposed in terms of frequencies. 30,000 hair cells. Images cannot be described so simply (jpeg encoding). 10,000,000 retinal cells. Images cannot be described so simply (jpeg encoding). 10,000,000 retinal cells. In both cases, fixing the input doesn’t help if the language/vision area of the cortex have not developed. In both cases, fixing the input doesn’t help if the language/vision area of the cortex have not developed.

34. Speech versus Vision But for speech, prelingual deaf children can learn to speak and hear. But for speech, prelingual deaf children can learn to speak and hear. Cochlear implants provide sufficient information to train the language areas of the cortex? Cochlear implants provide sufficient information to train the language areas of the cortex? And/or Chomsky may be right, syntax may be largely innate. And/or Chomsky may be right, syntax may be largely innate. Retinal implants have a very long way to go to catch up to Cochlear implants. Retinal implants have a very long way to go to catch up to Cochlear implants.