Speech perception

Previous research has demonstrated that sensitivity to unimodal nonnative speech
contrasts generally narrows during the first year. Although other work has demonstrated
a processing advantage for multimodal stimuli, research on infants' responsiveness to
nonnative contrasts so far has not examined whether concurrent auditory and visual
speech information can modulate perceptual narrowing. Thus, the current study
investigated the influence ofbimodally specified speech sounds on infants' sensitivity to
a nonnative phonemic contrast. Six-month-old and 10- to 12-month-old infants were
tested in a habituation/test procedure for discrimination of an audiovisual nonnative
speech contrast (Hindi /tal dental vs. /Tal retroflex stop). Findings showed that infants at
both ages exhibited evidence of discrimination following habituation to one of the speech
sounds. These findings suggest that the usually observed decline in responsiveness to
nonnative speech contrasts is limited to audibly specified contrasts and that concurrent
visual speech information enhances the discriminability of such contrasts.

This experiment investigated the role of sentence meaning in auditory language comprehension. Tokens from a GOAT-COAT speech voicing continuum were embedded in carrier sentences that were biased toward either a "goat" or "coat" interpretation and presented to subjects for a word identification task. The identification function showed a boundary shift in favor of the biased context, and an interaction localized to the ambiguous boundary region. Response times were largest in the boundary region and the interaction between the two factors was localized to the boundary region and the voiced endpoint. There was also a response time advantage for context consistent responses specifically in the boundary region. These results and those of earlier research (Connine, 1987; Connine & Clifton, 1987) are described in terms of interactive activation of potential response categories by acoustic parameter and sentence context.

This study investigated the interaction of acoustic and semantic information for phoneme categorization during sentence comprehension. Voice onset time (VOT) was manipulated to form a goat-to-coat voicing continuum; target stimuli from this continuum were embedded in sentences biased toward `goat' or `coat'. Sentences were presented in conjunction with three distinct experimental tasks and several temporal positions. Experiment 1A used a cross-modal identification task (Borsky, Tuller, and Shapiro, 1998) to cue stimulus identification at the target; the results showed sentence context biases on identifications and sentence context congruency effects on response times for mid-range stimuli. Experiment 1B used a cross-modal identification task 450 ms after the target; results showed sentence biases on identifications that extended to the endpoints and no sentence context congruency effects on response times. Experiment 2 used a cross-modal interference task (CMI) with the same auditory stimuli. The primary task was listening to the sentences for comprehension; the interference task was a word/non-word decision to an unrelated visual probe that appeared at one of three temporal positions. This was the only task for which no explicit judgments about the identity of the target were required. Response times at the embedded target showed a significant effect of VOT only. The 450 ms later probe position showed a significant VOT x Context interaction; response times were significantly longer for endpoint stimuli when sentence meaning was biased toward the opposite endpoint. These results were interpreted as initially context-independent phonological processing followed by context integration. Experiment 3 used a word-monitoring task; subjects saw the word `goat' or `coat' briefly on a computer screen, then listened to the same sentence stimuli used for the other experiments. The task was to press a button as soon as the monitoring target was heard in the sentence. Results showed that sentence context did not bias identifications. However, response times were significantly longer when sentence context was incongruent with the monitoring target. Taken together, the results of the three distinct tasks support an account of phonological processing in which phoneme categorization is initially independent unless an explicit judgment about the identity of the target is required.