Figure 1. Visual cortex responses to speech.

(A) The speech stimuli consisted of audiovisual recordings of a female talker speaking words (AV) edited so that only the visual portion of the recording was presented (Vis) or only the auditory portion of the recording was presented (Aud). Subjects were instructed to fixate the talker’s mouth (AV and Vis conditions) or a fixation point presented at the same screen location as the talker’s mouth (Aud condition). (B) In eight subjects, a total of 73 responsive occipital electrodes were identified. Electrode locations (black circles) are shown on a posterior view (top) and a medial view (bottom) of the left hemisphere of a template brain. (C) Broadband responses (70–150 Hz) to AV (solid line), Vis (dashed line) and Aud (dotted line) speech averaged across electrodes. The red arrow indicates the first time point (400 ms) at which the response to Vis speech was significantly greater than the response to AV speech. On the x-axis, time zero corresponds to the onset of the video (V) followed by the onset of the talker’s mouth movements (M) at 200 ms and onset of auditory speech (A) at 283 ms (orange arrows). (D) The broadband response enhancement (Vis – AV) measured from 200 to 1500 ms. One symbol per electrode (symbols jittered along x-axis for improved visibility).