On-line plasticity in spoken sentence comprehension: Adapting to time-compressed speech

Abstract

Listeners show remarkable flexibility in processing variation in speech signal. One striking example is the ease with which they adapt to novel speech distortions such as listening to someone with a foreign accent. Behavioural studies suggest that significant improvements in comprehension occur rapidly--often within 10-20 sentences. In the present experiment, we investigate the neural changes underlying on-line adaptation to distorted speech using time-compressed speech. Listeners performed a sentence verification task on normal-speed and time-compressed sentences while their neural responses were recorded using fMRI. The results showed that rapid learning of the time-compressed speech occurred during presentation of the first block of 16 sentences and was associated with increased activation in left and right auditory association cortices and in left ventral premotor cortex. These findings suggest that the ability to adapt to a distorted speech signal may, in part, rely on mapping novel acoustic patterns onto existing articulatory motor plans, consistent with the idea that speech perception involves integrating multi-modal information including auditory and motoric cues.

Fig. 1

Presentation of blocks of normal-speed (N) sentences and time-compressed (TC) sentences (top) in the experiment, plus sequence of events in the presentation of one sentence (bottom).

Fig. 2

Behavioural results in the scanner (In-scanner) and outside the scanner in the post-test (Post-test) for the average error rates (top) and the average response times (bottom). Averages for the error rates and response times are represented per mini-block of 4 sentences (black error bars, 4 per block) and averaged across the blocks (1–4) of 16 sentences (underlying grey bars). The averages for blocks 1–4 (16 sentences per block) were used for analysing both the behavioural and functional imaging data. Filled circles represent a mean over subjects of a four-sentence mini-block and error bars represent standard error of the mean. Dark bars refer to normal-speed sentences and lighter bars indicate time-compressed (TC) sentences.

Fig. 3

Activation for time-compressed relative to normal sentences (green) is superimposed on activation for all sentences relative to the fixation baseline (red) and shown on the mean structural image from the 18 participants.

Fig. 4

Adaptation-related activation patterns in the left (top row) and right (bottom row) hemispheres are shown in blue superimposed on all sentences relative to baseline (red). For each of the four regions, bar plots indicate changes in BOLD signal relative to baseline for the four blocks of normal sentences (orange) and the four blocks of time-compressed sentences (blue).