Adaptation and contrast in the perception of voicing

The results of experiments using selective adaptation with stop consonants have been interpreted in terms of auditory feature detector fatigue, phonetic feature detector fatigue, and response contrast. In the present studies, both a selective adaptation procedure and a procedure involving paired comparisons between successively presented stimuli were used to sort out these explanations. A fricative-stop-vowel syllable ([spa]) was constructed using an [s], followed by 75 msec of silence, followed by a 10-msec voice onset time [ba]. The perceived phonetic identity of this syllable was [p] even though the spectral structure of the stop vowel within this syllable was identical to a stimulus from the [ba] end of a [ba]-[pha] test series. As adaptors, the [spa] and [ba] endpoint syllables had identical effects. In paired-comparison procedure, the [spa] caused an ambiguous test item to be labeled "B," whereas the [ba] caused the test item to be labeled "P." Results of these experiments indicate that neither response contrast nor phonetic feature detection are involved in selective adaptation effects found for a voicing stop-consonant series. Results are interpreted as supporting the position that selective adaptation effects arise at an early, auditory level of processing that is responsive to the spectral overlap between adaptor and test items.