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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 Tactaid 7 Electric shock on sides of fingers One electrode per range of frequency Vibro-tactile stimulation on sternum, abdomen, forearm or neck Tacticon 1600 http://us.st11.yimg.com/us.st.yimg.com/I/audiologic alengineering_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- vs. Vibro-Tactile Stimulation ElectroPros 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 VibroPros Less variation in sensation Comfort Cons More power consumption - 138 mW per 4 mm electrode Harder to attach More complex construction Placement In the ear Pros Cons Less space for differentiation More complex construction Behind the ear Pros Mostly concealed from outsiders Easy access to hearing aid Cons Completely concealed from outsiders Attachment impeded by hair Neck Pros Most space for tactile layout Easiest construction Cons Easily noticeable to outsiders Alternative Design 1 & 2 Design 1 Design 2 Electro-Neck 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 Design Matrix Power Consumption ElectroNeck 5 Vibro-Ear Electro-Ear 1 5 Safety 4 5 4 Ease of Manufacturing 4 2 4 Patient Comfort 3 4 4 Aesthetics 2 4 4 18 16 21 Total 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. QUESTIONS