Evaluation and integration of acoustic features in speech perception

Identification of synthetic stop consonants as either /bae/, /pae/, /dae/, or /tae/ was examined in two experiments in which the stimuli varied independently on voice onset time (VOT), the consonantal second and third formant (F2-F3) transitions and, in experiment 2, the intensity of the aspiration noise during the VOT period. In both experiments, the patterns of the resulting identification probabilities were complex, but systematic, functions of each of the independent variables. Of most interest was the fact that the likelihood of identifying a stimulus to be /bae/ or /pae/, rather than /dae/ or /tae/, was strongly influenced by the VOT as well as by the F2-F3 transitions. Analogously, the likelihood of identifying a stimulus to be /bae/ or /dae/, rather than /pae/ or /tae/, depended on the F2-F3 transitions as well as on VOT. Three explanations of these results were considered within a fuzzy logical model of speech perception: (1) that there is interaction in the evaluation of acoustic features, (2) that the listener requires more extreme values of acoustic features for some speech sounds than for that of other speech sounds, and (3) that the aspiration noise during the VOT period serves as an independent acoustic feature to distinguish /pae/ and /bae/ from /tae/ and /dae/.