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 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  Electro-  Pros Less power consumption – 1.2mW per 3 mm electrode Smaller Easier construction  Cons Potential for shock and burns v. large current) Sensation quality varies Limited dynamic range of sensation  Vibro-  Pros Less variation in sensation Comfort  Cons More power consumption mW per 4 mm electrode Harder to attach More complex construction

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

Design Matrix Electro- Neck Vibro-EarElectro-Ear Power Consumption 515 Safety454 Ease of Manufacturing 424 Patient Comfort 344 Aesthetics 244 Total181621

References  Krames Communications. (1995). Hearing Aids. [Brochure]. San Bruno, CA.  Audiological Engineering Corp. (n.d.) Tactaid 7. Retrieved 29 September, 2006 from

QUESTIONS