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Tactile Auditory Sensory Substitution. Ryan Thome, Sarah Offutt, Laura Bagley, Amy Weaver, Jack Page BME 200/300 October 20, 2006. Client: Veronica H. Heide, Au.D. Audible Difference Advisor: Mitchell E. Tyler, P.E., M.S. Dept. of Biomedical Engineering & Dept. of Ortho-Rehab Medicine
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Tactile Auditory Sensory Substitution Ryan Thome, Sarah Offutt, Laura Bagley, Amy Weaver, Jack Page BME 200/300 October 20, 2006
Client: Veronica H. Heide, Au.D. Audible Difference Advisor: Mitchell E. Tyler, P.E., M.S. Dept. of Biomedical Engineering & Dept. of Ortho-Rehab Medicine University of Wisconsin - Madison
Overview • Problem Statement • Background • Proposed Designs • Future Work • Questions
Problem Statement The goal is to design and develop an auditory substitution device that through the use of a digital hearing aid and either vibro- or electro-tactile stimulation can substitute for regional frequency hearing loss.
PDS Summary • Adjusts to user specific hearing loss • Works with digital hearing aid output • Use vibro- or electro- tactile stimulation • Not highly noticeable (discrete or aesthetically acceptable)
Sensory Substitution • Presenting environmental information absent in one sensory modality to another • Examples: • Long Cane - visual navigation substituted though touch • Sign Language - speech substitution through vision • Braille - visual text substitution though touch
High Frequency Hearing Loss • Sensorineural • Normal hearing = 50 – 20,000 Hz • Above 1,000 Hz is lost • Loss of ability to hear certain high frequency consonants • Like hitting piano key with no strings Krames Communications.
Existing Devices • Tickle Talker • Electric shock on sides of fingers • One electrode per range of frequency • Tactaid 7 • Vibro-tactile stimulation on sternum, abdomen, forearm or neck • Tacticon 1600 http://us.st11.yimg.com/us.st.yimg.com/I/audiologicalengineering_1903_431188
Digital Hearing Aid • Two main types: In-the-ear (ITE) Behind-the-ear (BTE) • Frequency range 100 Hz – 7300 Hz • Takes analog waveform and converts it to string of numbers • Gain processing, digital feedback reduction, noise reduction, speech enhancement
Sound Processing Unit • Obtains high frequency signal from hearing aid • Amplifies signal • Several channels of frequency • Channel signals corresponding tactile stimulus to fire
Electro- Pros Less power consumption – 1.2mW per 3 mm electrode Smaller Easier construction Cons Potential for shock and burns (only @ v. large current) Sensation quality varies Limited dynamic range of sensation Vibro- Pros Less variation in sensation Comfort Cons More power consumption - 138 mW per 4 mm electrode Harder to attach More complex construction Electro- vs. Vibro-Tactile Stimulation
Placement • In the ear • Pros • Completely concealed from outsiders • Cons • Less space for differentiation • More complex construction • Behind the ear • Pros • Mostly concealed from outsiders • Easy access to hearing aid • Cons • Attachment impeded by hair • Neck • Pros • Most space for tactile layout • Easiest construction • Cons • Easily noticeable to outsiders
Alternative Design 1 & 2 Design 1 Electro-Neck Design 2 Vibro-BTE
Proposed Design • Electro-BTE • Array of electrodes aligned vertically behind ear • Each electrode corresponds to certain frequency range • As frequency increases each corresponding channel signals the electrode
Future Work • Decide on components • Design and build signal processing unit • Determine two point discrimination threshold • Analyze signal from hearing aid and break into channels
References • Krames Communications. (1995). Hearing Aids. [Brochure]. San Bruno, CA. • Audiological Engineering Corp. (n.d.) Tactaid 7. Retrieved 29 September, 2006 from http://www.tactaid.com/tactaid71.html.
