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The effect of frequency change on discrimination of pulse bursts in an electrocutaneous tactual vocoder



The effect of frequency change on discrimination of pulse bursts in an electrocutaneous tactual vocoder



Journal of the Acoustical Society of America 77(3): 1192-1198



Tactual vacoders (artificial hearing sytems) transduce the acoustic energy of speech into patterns of stimulation that are presented to the skin. In an electrocutaneous tactual vocoder, energy within an acoustic-frequency band is generally represented at a particular skin locus by the rate or frequency of brief electrical pulse bursts. At present little is known about tactual sensitivity for changes in the frequency of brief, bipolar electrical pulses used in several current electrocutaneous vocoder designs. Accordingly, discrimination of frequency change of electrocutaneous bipolar signals was evaluated for standard frequencies of 48, 100, 148, 200 and 248 Hz at signal durations of 50, 100 and 250 ms. Bipolar pulses (height - 10 mA, width = 13 .mu.s) were presented on a single electrode placed slightly above and 8 cm to either the left or right of the navel. In a same-different task, 3 practiced subjects judged pairs of stimuli separated by an interstimulus interval (ISI) of 300 ms. For standard frequencies of 48 and 100 Hz, psychometric functions were similar for all subjects and all signal durations. For these frequencies, .DELTA. f/f [the Weber fraction] was constant at .apprx. 0.3. By contrast, for standard stimuli greater than 100 Hz, the Weber fraction increased dramatically as a function of both standard frequency and signal duration. In a 2nd, similar experiment the Weber fraction for a 248-Hz standard increased as ISI [interstimulus interval] was decreased below 300 ms. By contrast, ISI had little effect on sensitivity for standard stimuli of 48 and 100 Hz. Overall, these results suggest guidelines for possible intensity coding schemes for future electrocutaneous vocoder designs.

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Accession: 006644243

Download citation: RISBibTeXText

PMID: 3156905

DOI: 10.1121/1.392184


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