Tactile Auditory Sensory

SubstitutionRyan Thome, Sarah Offutt, Laura Bagley, Amy Weaver, Jack Page

BME 200/300October 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 StatementThe 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- vs. Vibro-Tactile Stimulation 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

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 DesignElectro-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 MatrixElectro-Neck

Vibro-Ear Electro-Ear

Power Consumption

5 1 5

Safety 4 5 4Ease of Manufacturing

4 2 4

Patient Comfort

3 4 4

Aesthetics 2 4 4

Total 18 16 21

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