Response bias account of selective adaptation

Abstract

A number of investigators have hypothesized the existence of specialized neurolinguistic mechanisms—feature detectors—as playing a role in the perception of speech. One of the strongest sources of support for feature detectors has come from the selective adaptation paradigm, in which it is supposed that adaptation causes neural fatigue in a feature detector. In this study, a signal detection theory model was developed for phoneme identification tests. Results from identifications of three series of stimuli (/abə-abə/, /bæ-dæ/, /bæ-pæ/) were analyzed using this model to answer two questions: (1) Is increased discriminability of stimuli near the phoneme boundary due to response bias? (2) Does the phoneme boundary shift after adaptation result from criterion movement, or from sensory changes consistent with a feature detector account? Findings indicate that while the phoneme boundary effect does not seem to be due to response bias, selective adaptation is accomplished by a criterion shift, rather than changes at a more basic level of perception. These results suggest that the adaptation effect thus provides no evidence for feature detectors. [Work supported by NSF.]