Lexical Integration of Continuous Acoustic Detail: Normal and Impaired Listeners

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Speech perception is a process of mapping continuous detail in the acoustic signal onto discrete units of meaning like words. Given the variability in the signal and speed at which it arrives, the system must cope with a great deal of variation in a small amount of time. The long term objective of this research is to understand how this process works. This proposal tests an implication of existing work showing that lexical activation is sensitive to continuous detail in the signal and for current models of spoken word recognition: that online lexical-activation processes (which are fast and work in parallel to build stable representations) can actively integrate continuous detail over time to anticipate upcoming material, resolve ambiguity in the past, and organize perceptual processes. This will be tested in four series of behavioral experiments based on visual world paradigm. In this paradigm, subjects hear carefully controlled spoken language and manipulate objects in a visual environment while eye-movements are monitored. The probability of fixating each object yields a moment-by-moment estimate of the activation for that word (how much the system is considering that word) as it unfolds over time. The first two projects examine these temporal integration processes in unimpaired listeners for the perception of phonologically modified speech and compensation for speaking rate. In each we will show that system can actively anticipate upcoming material and resolve ambiguous material in the past and that these processes are modulated by lexical factors. In the third project we explicitly test this framework examining situations in which continuous detail could facilitate ambiguity resolution, but only if it can retained longer than short-term echoic memory stores are known to operate. This would suggest that lexical processes play a unique role in this maintenance. The fourth project applies this framework to language impairments, testing the hypothesis that perceptual deficits associatedwith SLI originate in lexical, not perceptual, processes. Ultimately this project will contribute to basic knowledge of speech perception and its relationship to language disorders. Since perceptual and lexical abilities typically develop before higher level language, diagnostics and therapies based on them may be applied earlier (and as a result, more successfully) than other techniques. Thus, the basic knowledge acquired here may contribute to earlier detection and treatment of SLI.