1. Tactile Auditory Sensory Substitution
Jimmy Fong, Jack Page, Becky Jones, Ryan Thome, Matt Valaskey
BME 301
March 9, 2007

2. Dept. of Biomedical Engineering & Dept. of Ortho-Rehab Medicine
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
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.

4. Problem Statement
The goal is to design and develop an auditory substitution device that through the use of vibro-tactile stimulation can substitute for regional frequency hearing loss. The main focus of this semester is integrating vibro-transducers into the system in order to prepare the system for laboratory trials.

5. 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

6. Existing Devices Tactaid 7 Tickle Talker Tacticon 1600
Electric shock on sides of fingers
One electrode per range of frequency
Tickle Talker
Vibro-tactile stimulation on sternum, abdomen, forearm or neck
Tacticon 1600

7. PDS Summary
The device will substitute for high frequency hearing loss to the extent of helping the user in everyday communication.
Use vibro-tactile stimulation
Self contained, portable, discrete or aesthetically acceptable

8. System Diagram

9. Word Discrimination
Pairs of words that can be distinguished with device
Sixty versus Fifty
Shirt versus Church
Much versus Such
Sob versus Shop
Audio input is filtered for specific frequency range
Becomes separate channels
1: kHz – p, i, m
2: kHz – ch, sh
3: kHz – f
4: kHz – s, th

10. Sound Processing Unfiltered Sound Wave “Sixty – Fifty”
Frequency Filtered Sound Waves

11. Vibro-tactile Stimulation
Substitute hearing loss with vibration
Need to stimulate subcutaneous mechanoreceptors: Pacinian Corpuscles (FA II)

12. Vibro-tactile Stimulation
Konyo study indicates minimum threshold for detection:
1 mm ~5 Hz
1 μm ~200 Hz
Increased sensitivity at vibrations of 60 and 250 Hz
Density of mechanoreceptors less behind ear
Two point discrimination test

13. Vibro-tactile Stimulation
Series of 4 piezoelectric transducers
Transducer deflects varying with frequency input
Allows user to discern different phonemes by location of the stimulus

14. Vibro-tactile Pros & Cons
Comfortable compared to electro stimulation
Less variation in sensation
Cost effective
Ease of implementation
Cons
More power consumption
Larger 13 mm x 25 mm per electrode

15. Electro-tactile Stimulation
Create vibrating sensation by sending small currents through the skin
Typical currents range from 1-20 mA
Comfortable frequency around 15 Hz
High voltage (200 – 500 V) necessary to create current
Typical electrodes are gold or silver plated and a few millimeters in diameter

16. Electro-tactile Pros & Cons
Small power consumption
As small as 3 mm in diameter
Cons
Less comfortable than vibro stimulation
More variation in sensation
Complex implementation

17. Behind the Ear Placement
Specifications
Skull to skull and skin to skin tactors 25 mm apart unless stimulating at different frequencies
Skull to skin tactors 20 mm apart
2 tactors on skull bone, 2 on skin below
Learning curve to sensing the stimulations

18. Determining Consonants
Which stimulator should be activated?
Frequency approach
Stimulators and consonants related to certain frequencies
Linguistic approach
Consonants are variable and affected by neighboring sounds
Utilize voice recognition to determine specific consonants
Relate stimulation pattern to a linguistic sound or symbol

19. Design Matrices Stimulation Vibro Electro Power Consumption (10) 5 9
Safety (5) 4
Ease of Implementation (10) 2
Patient Comfort (5)
Aesthetics (5)
Total 24 21
Speech Analysis
Frequency
Linguistic
Accuracy (10) 7 8
Ease of Implementation (10) 9 1
Noise Adaptability (5) 2 4
Processing Time (5)
Cost (5) 5
Total 27 17

20. Future Work Integrate tactile transducers with circuit
Perform further speech analysis to better isolate fricative sounds
Test efficacy of device on human subjects
Miniaturize
Further test effectiveness of device placements on body

21. References
Krames Communications. (1995). Hearing Aids. [Brochure]. San Bruno, CA.
Audiological Engineering Corp. (n.d.) Tactaid 7. Retrieved 29 September, 2006 from
Kanyo, M. et al A Tactile Synthesis Method Using Multiple Frequency Vibrations for Representing Virtual Touch. IEEE/RSJ. p 1121 – 1127.