1. Tactile Auditory Sensory Substitution
Jimmy Fong, Jack Page, Becky Jones, Ryan Thome, Matt Valaskey
BME 402
March 7, 2008

2. Client: Veronica H. Heide, Au. D
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

3. High Frequency Hearing Loss
Normal hearing
50 – 20,000 Hz
Above 1,000 Hz is lost
Loss of ability to hear certain high frequency consonants
Hitting piano keys with no strings

4. Problem Statement
The goal is to design and develop an auditory substitution device that through the use of vibrotactile stimulation can substitute for regional frequency hearing loss. We will continue the work from the last three semesters, mainly focusing on refining the technical operation of the prototype and obtaining clinical testing data on the performance of the system.

5. Sensory Substitution Examples:
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

6. TASS Basics Pairs of words that can be distinguished with device:
Sound filtering results in channel to frequency breakdown of:
1: kHz – p, i, m
2: kHz – ch, sh, f
3: kHz – ch, sh
4: kHz – s, th
Diagram of basic handheld device:
User places each finger over one vibrating motor
Pairs of words that can be distinguished with device:
Sixty versus Fifty
Much versus Such
Vibrations:

7. Current State of Design
Standalone device disconnected from a PC
Audio processed on Texas Instruments DSP
Audio input through microphone
Real-time digital filtering - 4 frequency bands
Digital ON through digital outputs
when energy in band
Algorithms implemented in LabVIEW
Features adaptive algorithm to
adjust for environmental noise
Signals routed to LEDs and motor
driving circuits after processing

8. Current State of Design
Vibrational patterns presented to user on 4 motors
Handheld device - one motor per finger
Consonant sounds correspond to tactile pattern

9. Technical Refinements
Improve efficiency of signal processing
Research more powerful digital filters
More specific frequency bands
Decrease roll off
Improve adaptability of system to noisy environments

10. Testing
Goal: Show that our device effectively allows people with high frequency hearing loss to better comprehend oral communication by increasing word discrimination ability
Our testing procedure has been set up to prove this, incorporating all necessary controls to ensure the accuracy of our results

11. Testing Procedure 1. Preliminary Questions & Visual Inspection
2. Von Frey Hair Test
- Filaments up to 1 mm in diameter
- Ensure sensation in each fingertip, if there is doubt – repeat
- Gauge 6 fishing line, 0.4 mm

12. Testing Procedure 3. Stimulus testing and association
Slowly introduce subject to the substituting
stimulus
Pure tones  stimulate single tactor
Dual tones  stimulate multiple tactors
Example consonant sounds
Ensure subject can differentiate stimuli
and start to build associations
If there is doubt – can repeat

13. Testing Procedure
4. Baseline CCT performed to assess degree of hearing loss and level of unassisted consonant recognition
California Consonant Test (CCT)
Multiple choice consonant identification test
50 test words
Highly sensitive to high frequency hearing loss
Useful for assessing function of assistive or rehabilitative devices
Example word choices

14. Testing Procedure 5. Consonant discrimination
Single consonant sounds activate specific tactors
Test ability to identify consonants using device
Essential to being able to successfully use device with word recognition
Need 90% accuracy before moving to next test
6. CCT repeated with assistance of device
Same 50 words in different order
Main test to measure ability of the device to aid in word discrimination

15. Data Analysis Recruit and test 10 hearing impaired subjects
Paired data analysis will measure performance on baseline CCT against performance with the device
Data on preliminary tests will also be used to measure elements such as the learning curve of the device
Goal: To see improvements in CCT scores with device when compared to without the aid of the device, i.e. increased word recognition ability

16. Future Work Implement technical refinements
Test Subjects with High Frequency Hearing Loss
Analyze data from testing
Publish our findings in a Journal