Non-Linguistic Sentence-Length Precursors Affect Speech Perception: Implications for Speaker and Rate Normalization

Speech contexts can influence phonetic perception considerably, even across extended temporal windows. For example, manipulating spectral or temporal characteristics of precursor sentences leads to dramatic changes in categorization of subsequent vowels and consonants (e.g., Ladefoged & Broadbent, 1957; Summerfield, 1981). These findings often have been discussed in terms of speaker and rate normalization. The present study aimed to uncover precisely which types of information in the speech signal subserve such shifts in speech categorization. A series of experiments examined the influence of sentence-length non-speech precursors--series of brief pure tones--on the perception of speech segments with which they shared critical spectral and temporal properties. Across multiple experimental manipulations, the non-speech precursors affected the perceived place (alveolar, velar) and manner (stop, glide) of articulation of synthesized English consonants. Effects were observed even when non-speech precursor series were temporally-nonadjacent to the speech categorization targets and even when multiple interrupting acoustic events separated precursor and target. Both category boundary shifts and changes in graded internal category structure were observed. These results indicate that the auditory system is sensitive to both spectral and temporal information conveyed by non-linguistic sounds across sentence-length temporal windows. Moreover, this sensitivity influences speech categorization, highlighting that general auditory processing may play a role in the speech categorization shifts described as rate and speaker normalization.