This study examined the effect of sentence context and local acoustic structure on phoneme categorization. Target stimuli from a 10-step GOAT-COAT continuum, differing only on a temporal cue for voice onset time (VOT), were embedded in carrier sentences that biased interpretation toward either "goat" or "coat." While subjects listened to the sentences they also responded as quickly as possible to a visual probe by indicating whether the probe matched the target stimulus they heard. Results showed that the interaction of VOT and sentence context significantly affected both identification and RT for stimuli near the perceptual boundary; the identification function showed a boundary shift in favor of the biased context and peak response times for each context reflected the shifted identification boundaries. In addition, response times were faster for identification of stimuli near the category boundary when responses were congruent, rather than incongruent with the sentence context. The response time differences for congruent versus incongruent responses in the boundary region are interpreted as depending on the results of initial phonological analysis; potentially ambiguous categorizations may be subject to additional evaluation in which a context-congruent response is both preferred and available earlier.

This article describes how we and others have exploited online methodology to investigate normal and disordered language processing in adults. Online tasks can be used to measure effects occurring at various temporal points during ongoing processing and are often sensitive to fast-acting, automatic processes, as well as to processes that rely on the integration and interaction of several types of information. Online tasks can be compared to their offline counterparts, tasks such as sentence-picture matching, categorization, word generation and repetition. These tasks are often used by clinicians as part of their assessment and treatment repertoire and measure effects observed at the end-points of perhaps several processes. They can thus mask a patient's strengths (and weaknesses) in any single area, including subcomponents of the language domain. We review several online lexical and syntactic processing experiments and end with a discussion of the clinical benefits of this work.

In spoken language, local acoustic information is frequently consistent with more than one phoneme. This study investigates the influence of acoustic and semantic information on phoneme categorization as a sentence unfolds in time. Ten target stimuli forming a Goat-to-Coat continuum were created from natural speech by manipulating the voice onset time of the initial consonant. These stimuli were embedded in biased sentences such as: Goat-biased: The busy dairyman forgot to milk the (Goat/Coat) in the drafty barn. Coat-biased: The careful tailor hurried to press the (Goat/Coat) in the cluttered attic. A cross-modal interference task showed immediate effects of acoustic information; effects of semantic information appeared 450 ms later. A cross-modal identification task showed immediate sentence context effects for ambiguous mid-range stimuli while identifications 450 ms later showed context effects for endpoint stimuli. A word monitoring study showed immediate context effects throughout the acoustic parameter range. These data support an account of auditory sentence comprehension in which semantic information does not immediately and automatically influence phonological analysis of an acoustic signal; contextual influences occur over time or when a task or situation requires explicit judgment about the identity of a stimulus. [Work supported by NIMH, Grant No. MH42900, and NIH, Grant No. DC00494.]

The purpose of this study was to investigate the temporal unfolding of local acoustic information and sentence context using both cross-modal interference (CMI) and word-monitoring tasks. The timing of sentence context effects have important theoretical implications for models of language processing (e.g., initial context independence vs. initial interaction). Yet, different tasks tend to yield different results. For both experiments, stimuli from an acoustically manipulated "goat-to-coat" continuum were embedded in sentences whose interpretation was biased toward either "goat" or "coat." In experiment 1 (CMI), the primary task was listening to sentences for comprehension; the interference task was a word/nonword decision to an unrelated visual probe that appeared at one of three positions within the sentence. Results showed immediate effects of the acoustic manipulation, but only delayed effects of sentence context. These results were interpreted to indicate that phonological processing is initially context-independent but is followed by rapid context integration. Experiment 2 used a word-monitoring task: Response times were significantly longer when sentence context was incongruent with the monitoring target, showing an immediate effect of context. The apparently contradictory results of the two experiments together support an account of language processing in which phoneme categorization is initially independent of sentence context unless an explicit judgment about the identity of the target is required.

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