Category Boundaries for Speech and Nonspeech Sounds
James R. Sawusch, David B. Pisoni · The Journal of the Acoustical Society of America · 1974
Recent experiments employing an adaptation paradigm have demonstrated the possibility of phonetic feature detectors in speech perception (Eimas and Corbit, 1973). These results could be explained by Adaptation Level Theory (ALT), assuming the reference for categorizing a speech sound is external. In the present experiment, identification functions were obtained for a series of synthetic speech sounds ranging perceptually from /ba/ to /pa/ and a series of tones varying in intensity from 60 to 84 dB SPL. The distribution of occurrences of each stimulus in a series was varied for both tones and speech stimuli. The category boundaries for the tones shifted as a function of the relative number of occurrences of each tone as predicted by ALT. However, the phonetic boundaries for the speech stimuli failed to show the analogous shift. These results suggest that the response criteria for phonetic boundaries may be mediated by an internally generated reference. In contrast, the reference for the nonspeech category boundaries is under external stimulus control.