Contingent categorisation in speech perception

Abstract

The speech signal is notoriously variable, with the same phoneme realised differently depending on factors like talker and phonetic context. Variance in the speech signal has led to a proliferation of theories of how listeners recognise speech. A promising approach, supported by computational modelling studies, is contingent categorisation, wherein incoming acoustic cues are computed relative to expectations. We tested contingent encoding empirically. Listeners were asked to categorise fricatives in CV syllables constructed by splicing the fricative from one CV syllable with the vowel from another CV syllable. The two spliced syllables always contained the same fricative, providing consistent bottom-up cues; however on some trials, the vowel and/or talker mismatched between these syllables, giving conflicting contextual information. Listeners were less accurate and slower at identifying the fricatives in mismatching splices. This suggests that listeners rely on context information beyond bottom-up acoustic cues during speech perception, providing support for contingent categorisation.