The essential role of premotor cortex in speech perception

Abstract

Besides the involvement of superior temporal regions in processing complex speech sounds, evidence suggests that the motor system might also play a role [1-4]. This suggests that the hearer might perceive speech by simulating the articulatory gestures of the speaker [5, 6]. It is still an open question whether this simulation process is necessary for speech perception. We applied repetitive transcranial magnetic stimulation to the premotor cortex to disrupt subjects' ability to perform a phonetic discrimination task. Subjects were impaired in discriminating stop consonants in noise but were unaffected in a control task that was matched in difficulty, task structure, and response characteristics. These results show that the disruption of human premotor cortex impairs speech perception, thus demonstrating an essential role of premotor cortices in perceptual processes.

Conflict of interest statement

Conflict of interest The authors declare no conflict of interest.

Figures

Figure 1

Representative fMRI activation peaks for speech perception for two subjects. Regions selected for stimulation are shown in bright colors; peak coordinates in these regions were used as targets for TMS in the main experiment. Other activated regions are shown in faded colors. (a) Left premotor cortex (PMC). Arrowheads show the location of the central sulcus. (b) Left superior temporal gyrus (STG).

Figure 2

Percentage rate of correct answers for each task (phonetic discrimination, color discrimination) and each TMS site (baseline, PMC, STG). Error bars show standard error of the mean. TMS over PMC induced significant decrease of correct responses in the phonetic discrimination task, whereas TMS had no effect on the control task of color discrimination. TMS to STG did not affect performance of either task.

Figure 3

Percentage rate of correct answers for each task for the subgroup (n=12) performing an additional tone perception task. The TMS sites were the same like in the main group (baseline, PMC, STG). Error bars show standard error of the mean. Like in the entire group of subjects, TMS over PMC induced significant decrease of correct response rate in the phonetic discrimination task but not in the tone discrimination task. In contrast, TMS over the superior temporal gyrus indiced a decrease of performance in the tone perception task. However, ANOVA analysis of the subgroup data revealed a main effect of TMS condition but no significant task × TMS condition interaction, indicating that both regions play a role in the auditory perception processes tested.