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Tactile Auditory Sensory Substitution Jimmy Fong, Jack Page, Becky Jones, Ryan Thome, Matt Valaskey BME 301 March 9, 2007 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 Electric shock on sides of fingers One electrode per range of frequency Vibro-tactile stimulation on sternum, abdomen, forearm or neck Tacticon 1600 http://us.st11.yimg.com/us.st.yimg.com/I/audiologic alengineering_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 Person Speaking Audio Waves Microphone Analog Voltage Signal Multi-channel Amplifier/ Comparator Digital Signal Analog Voltage Signal Sound Card Amplified Analog Voltage Signal Transducers Vibrational Pulses User Cool Edit Digital Signal that has been filtered to specified frequency, amplitude, and channel divisions 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: 2: 3: 4: 1.6-2.0 2.0-3.0 3.0-3.5 4.5-8.0 kHz kHz kHz kHz – – – – p, i, m ch, sh f 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 Pros 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 Pros 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 4 Ease of Implementation (10) 9 2 Patient Comfort (5) 4 2 Aesthetics (5) 2 4 24 21 Frequency Linguistic Accuracy (10) 7 8 Ease of Implementation (10) 9 1 Noise Adaptability (5) 2 4 Processing Time (5) 4 2 Cost (5) 5 2 27 17 Total Speech Analysis Total 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.