The Relation between Identification and Discrimination along Speech and Non-Speech Continua

Abstract

In order to investigate the perception of simple unidimensional non-speech stimuli and synthetic speech stimuli in a manner permitting direct comparisons, identification and discrimination functions were obtained by the method of ABX for three series of duration stimuli, one series of reflectance stimuli, and a series of speech sounds, the stop consonants /b, d, g/. These results were also compared with those from earlier studies investigating synthetic vowels (/i, e, ε, æ/) and consonants (/d, t/). Identification of the consonants was marked by abrupt transitions between phonemic categories and small context effects, while discrimination functions demonstrated greater discriminability between rather than within categories. Moreover, discrimination functions predicted from identification responses were close approximations of the obtained discrimination. Thus, perception of the consonants was essentially categorical. Vowel perception, however, was continuous: the identification functions showed less steep boundaries, discriminability was quite acute for all stimuli, and, unlike the stops, considerably better than identification. in addition, identification of the vowels was found to be greatly influenced by context. Perception of non-speech stimuli was much like that of the vowels, though category boundaries were more abrupt and context effects were less. The data were in accord with a motor theory of speech perception whereby the perceptual event is cued directly by neural representations of feedback stimulation arising from articulatory movements. This is in contrast to perception of non-speech stimuli which is cued directly by the external stimulation.