Perception of multiple electrode stimulus patterns: implications for design of an electrotactile speech processor.

Identification of multiple-electrode stimulus patterns was evaluated in nine adult subjects, to assess the feasibility of providing additional speech information through the tactual display of an electrotactile speech processor. Absolute identification scores decreased from 97.8% for single electrodes, to 61.9% for electrode pairs, and, to 31.8% for electrode triplets. Although input information increased with paired-and triple-electrode stimuli, information transmission scores were not significantly increased for either electrode pairs (2.99 bits) or triplets (2.84 bits) as compared with single electrodes (2.84 bits). These results suggest that speech coding strategies using stimulus patterns of electrode pairs or triplets would provide little improvement beyond that found for the present single-electrode scheme. However, higher absolute identification scores (73.6%), and an increase in information transmission to 3.88 bits, were recorded for test stimuli containing all combinations of paired and single electrodes. Based on this finding, two stimulus sets using a restricted number of combinations of paired and single electrodes were evaluated. The two stimulus sets simulated the spatial patterns of paired and single electrodes arising from use of alternative speech coding schemes to increase consonant voicing information. Results for the two stimulus sets showed higher electrode identification scores (79.7% and 90.4%), as compared with paired-electrode stimuli. Although electrode identification score was not as high as for single electrodes, information transmission was increased to 3.31 bits for the VF2 stimulus set. Analysis of the responses also showed that scores for identification of simulated voicing information conveyed by the two stimulus sets were 99.4 and 90.4% correct.(ABSTRACT TRUNCATED AT 250 WORDS)