Artificial Cochlear Implants Geoff Norman 4/18/16 Abstract: Cochlear implants are surgically implanted electronic devices which allow people who are deaf to have a sense of hearing. These devices work by picking up sound waves thorough a microphone which then transmits electrical signals to electrodes that are planted within the cochlear nerve. Once a microphone signal is received the electrodes stimulate the cochlear nerve which then sends signals to the brain that simulate hearing.

Outline Brief history of artificial hearing. How are cochlear implants different from normal hearing? Summary of normal hearing. Summary of cochlear implant hearing. How does a cochlear implant work? Overview of circuit architecture. Breakdown of circuit architecture into main components. Example of normal vs implant hearing.

Brief History of Artificial Hearing Early 19th century: Alessandro Volta stimulates inner ear using a battery and two metal rods. 1930: Wever and Bray discover that electrically stimulating the auditory nerve with electrodes was similar to stimulation using sound waves. 1950: Lundberg stimulates auditory nerve using electricity while performing surgery. 1972: Speech processor developed. 1984: FDA formally approves cochlear implants for use in patients with severe hearing loss.

Mechanisms of Normal Hearing Outer Ear Consists of Pinna, Ear Canal, and Eardrum. Captures and locates sound sources. Middle Ear Consists of the Malleus, Incus, and Stapes. Transmits vibrations from the Eardrum to the Inner Ear. Inner Ear Consists of Cochlea, organ of Corti, and Basilar Membrane. Converts vibrations to spatiotemporal patterns. [1]

Mechanisms of Cochlear Implant Hearing External Devices Microphones Speech Processor Transmitter Internal Devices Receiver Stimulator Electrode Array [4]

Cochlear Implant Architecture [6]

Microphone Piezoelectric microphones are typically used. When the piezoelectric material is stressed along one axis it induces a potential difference across an orthogonal axis thereby directly transducing pressure waves into electrical waves. Broad frequency spectrum that doesn’t extend to low frequencies to avoid picking up head movements. [10]

Speech Processor Decomposes complex signals from the microphone into discrete electrical signals. Upon entering the speech processor frequency resolution is performed on the signals to split them into their frequency components. Once split into their frequency components amplitude compression is performed to lessen the effect of the effect of louder signals and to amplify the effect of quieter signals. Finally, pulse modulators are used to turn the various signals into biphasic pulses that can be transmitted to the stimulator. [8]

Transmitter/Receiver Consists of an encoder, a decoder, an external transmitting coil and an internal receiving coil. Signals from speech processor are encoded and sent from external coil to internal coil. Once the signal is received by the internal coil it is decoded and sent to the stimulator. [9]

Stimulator/Electrode Array The stimulator receives the decoded electrical signal from the receiver coil and uses the signal to properly stimulate the electrode array at various positions. The electrode array is placed within the cochlea and when stimulated properly will cause the ganglion cells to send impulses to the part of the brain responsible for hearing. [10]

Example of Cochlear Implant Sound [5]

References [1] Appalachian State, http://www1.appstate.edu/~kms/classes/psy3203/Ear/Eardrawing1.jpg. 2016. [2]"Cochlear implant", Wikipedia, 2016. [Online]. Available: https://en.wikipedia.org/wiki/Cochlear_implant#Efficacy. [Accessed: 09- Apr- 2016]. [3]"Hearing", Wikipedia, 2016. [Online]. Available: https://en.wikipedia.org/wiki/Hearing. [Accessed: 09- Apr- 2016]. [4]"About Cochlear Implants — The Children's Cochlear Implant Center at UNC", Med.unc.edu, 2016. [Online]. Available: https://www.med.unc.edu/earandhearing/listening/about-cochlear-implants-1. [Accessed: 09- Apr- 2016]. [5]"Hearing Cochlear Implants w/ open captions - YouTube", Youtube.com, 2012. [Online]. Available: https://www.youtube.com/embed/00WOao4kpwM. [Accessed: 09- Apr- 2016]. [6]"Human-Embedded Computing", www.cs.uaf.edu, 2009. [Online]. Available: https://www.cs.uaf.edu/2009/fall/cs441/proj1/natasa/index.html. [Accessed: 09- Apr- 2016].

References (continued) [7]"History of Cochlear Implants timeline.", Timetoast, 2016. [Online]. Available: https://www.timetoast.com/timelines/history-of-cochlear-implants. [Accessed: 10- Apr- 2016]. [8]"Understanding The Cochlear Implant: Components : Speech Processor", Biomed.brown.edu, 2006. [Online]. Available: http://biomed.brown.edu/Courses/BI108/2006-108websites/group10cochlearimplant/pages/speechprocessor.htm. [Accessed: 10- Apr- 2016]. [9]"Electrodes and Channels", cochlear implant HELP, 2012. [Online]. Available: https://cochlearimplanthelp.com/journey/choosing-a-cochlear-implant/electrodes-and-channels/. [Accessed: 13- Apr- 2016]. [10]"Microphones", Hyperphysics.phy-astr.gsu.edu, 2016. [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/audio/mic3.html. [Accessed: 14- Apr- 2016].

Summary of Key Points Cochlear implants are electrical devices that can be implanted directly into a deaf patient that allows the patient to experience a simulation of hearing. Piezoelectric microphones are used to transduce sound waves into electrical signals that can be used by the implant to simulate sound. A speech processor is used to take the complex microphone signal and decompose it into discrete electrical signals which are easier to interpret. A radio frequency receiver and transmitter are used to send the speech processor data to the stimulator and electrode array. An electrode array is used to directly stimulate the cochlea with different electrical signal that represent the original sound waves frequency and amplitude.