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

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

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.

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.

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

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 http://us.st11.yimg.com/us.st.yimg.com/I/audiologicalengineering_1903_431188

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

System Diagram

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: 1.6-2.0 kHz – p, i, m 2: 2.0-3.0 kHz – ch, sh 3: 3.0-3.5 kHz – f 4: 4.5-8.0 kHz – s, th

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

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

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

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

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

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

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

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

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

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

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

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. Kanyo, M. et al. 2005. A Tactile Synthesis Method Using Multiple Frequency Vibrations for Representing Virtual Touch. IEEE/RSJ. p 1121 – 1127.