Talker and sentence variability attenuates speaking rate normalization in speech perception

Abstract

Speech perception is shaped by acoustic context effects, where acoustic properties of earlier (context) sounds influence categorization of later (target) sounds. These context effects are sensitive to talker characteristics. When context sentences were spoken by a different talker on each trial, spectral contrast effect (SCE) magnitudes affecting categorization of the target vowel were smaller than when sentences were spoken by a single talker [Assgari and Stilp, J. Ascoust. Soc. Am. (2015)]. Here, perceptual consequences of talker variability were examined in Temporal Contrast Effects (TCEs; also termed rate normalization). Each trial presented a context sentence (spoken at a fast or slow rate) followed by a target word varying from “deer” to “tier.” Context sentences were the same stimuli from Assgari and Stilp (2015): one talker speaking the same sentence on each trial, one talker speaking a different sentence on each trial, and 200 talkers each speaking a different sentence on each trial. TCE magnitudes significantly decreased between One Talker/One Sentence and One Talker/200 Sentences, and again between One Talker/200 Sentences and 200 Talkers/200 Sentences. Conversely, in Assgari and Stilp, talker variability diminished SCEs but sentence variability for a single talker did not. These results suggest that variability in different acoustic domains restricts speech perception.