Lexical Influences on Auditory Streaming

Biologically salient sounds, including speech, are rarely heard in isolation. Our brains must therefore organize the input arising from multiple sources into separate “streams” and, in the case of speech, map the acoustic components of the target signal onto meaning. These auditory and linguistic processes have traditionally been considered to occur sequentially and are typically studied independently [1Bregman A.S. Auditory Scene Analysis: The Perceptual Organization of Sound. M.I.T. Press, Cambridge1990Crossref Google Scholar, 2Pisoni D.B. Remez R.E. The Handbook of Speech Perception. Blackwell, Oxford2005Crossref Scopus (1) Google Scholar]. However, evidence that streaming is modified or reset by attention [3Carlyon R.P. Cusack R. Foxton J.M. Robertson I.H. Effects of attention and unilateral neglect on auditory stream segregation.J. Exp. Psychol. Hum. Percept. Perform. 2001; 27: 115-127Crossref PubMed Scopus (271) Google Scholar], and that lexical knowledge can affect reports of speech sound identity [4Elman J.L. McClelland J.L. Cognitive penetration of the mechanisms of perception: Compensation for coarticulation of lexically restored phonemes.J. Mem. Lang. 1988; 27: 143-165Crossref Scopus (167) Google Scholar, 5Shoaf L.C. Pitt M.A. Does node stability underlie the verbal transformation effect? A test of node structure theory.Percept. Psychophys. 2002; 64: 795-803Crossref PubMed Scopus (18) Google Scholar], suggests that higher-level factors may influence perceptual organization. In two experiments, listeners heard sequences of repeated words or acoustically matched nonwords. After several presentations, they reported that the initial /s/ sound in each syllable formed a separate stream; the percept then fluctuated between the streamed and fused states in a bistable manner. In addition to measuring these verbal transformations, we assessed streaming objectively by requiring listeners to detect occasional targets—syllables containing a gap after the initial /s/. Performance was better when streaming caused the syllables preceding the target to transform from words into nonwords, rather than from nonwords into words. Our results show that auditory stream formation is influenced not only by the acoustic properties of speech sounds, but also by higher-level processes involved in recognizing familiar words.