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

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

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

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.

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

TASS Basics Pairs of words that can be distinguished with device: Sound filtering results in channel to frequency breakdown of: 1: 1.6-2.0 kHz – p, i, m 2: 2.0-3.0 kHz – ch, sh, f 3: 3.0-3.5 kHz – ch, sh 4: 4.5-8.0 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 1 2+3 4 2+3 Vibrations: 4 4 2

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

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

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

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

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

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

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

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

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

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