Categorical perception of /b/ and /w/ during changes in rate of utterance

Abstract

Normal sentences containing the sound /w/ were tape recorded and digitized. A normal and a “fast” token of each sentence was stored in a PDP 11-10 computer. The “fast” tokens were created via a pitch-synchronous segmentation program wherein segmentation lines were interactively applied at the zero axis crossing at the beginning of each periodic waveform, and at similar periodic intervals during voiceless speech sounds. Deletion of every third interval resulted in a token of the sentence, increased in rate by one-third. The test consonants plus following vocalic transitions were similarly segmented (11 segments approximately 9 msec each). A recursively applied deletion program allowed alteration of the slope of the CV transitions in 11 steps in both normal and fast utterances. Listeners randomly heard ten presentations of each slope condition for each test sentence at each rate of utterance. Rapid slope changes were heard by listeners as /b/ and more gradual slope changes as /w/. During changes in rate of utterance, the categorical boundary between /b/ and /w/ was shifted toward a steeper slope. The results of this study are discussed in regard to the temporal relativity of categorical boundaries.