Comparison of tactual and auditory discrimination of speech

The relationship between tactual and auditory perception of speech was investigated by presenting two speech continua to subjects via a 32-channel computer controlled electrocutaneous display and via normal audition. The stimuli were synthetic /a/ to /ə/ and /sta/ to /sa/ with 9 equally spaced intermediate stimuli between each endpoint yielding two 11-step continua. Five well-practiced adults performed three tasks: (1) an adaptive discrimination task using each of the endpoints as target stimuli; (2) a standard identification procedure (all 11 steps categorized as either endpoint 1 or 11); and (3) a same-different task (equal interval stimuli were discriminated across the continuum). For tactual discrimination, channel information was presented in three spectral configurations conforming to (1) logarithmic, (2) linear, and (3) average (arithmetic mean of log and linear) filtering. Results indicate (a) a close correspondence between auditory and tactual perception, (b) subphonemic discrimination in both modalities, (c) categorical perception in both modalities, and (d) a more auditorylike pattern with log and average filter configurations than with linear. Implications in terms of theories of speech perception will be discussed.