(A) Medial view of a cortical surface model of the left hemisphere brain of a single subject (anonymized subject ID YAI). Posterior electrode e81 (red circle) was located superior to the calcarine sulcus on the occipital pole (red circle) while anterior electrode e65 (blue circle) was located inferior to the calcarine on the medial wall of the hemisphere. The receptive field mapping stimulus consisted of a small checkerboard presented at random screen locations while subjects performed a letter detection task at fixation (not shown). (B) The responses evoked by the mapping stimulus in electrodes e81 (left panel) and e65 (right panel). Color scales corresponds to the amplitude of the visual evoked response at each location in the visual field, with the crosshairs showing the center of the visual field and the red and blue circles showing the center of a two-dimensional Gaussian fitted to the response. Electrode e81 had a central receptive field (eccentricity at RF center of 2.5°) while electrode e65 had a peripheral receptive field (eccentricity 10.9°). (C) The receptive field location for the two sample electrodes, e81 (red circle) and e65 (blue circle) are shown on the speech stimulus. Subjects were instructed to fixate the talker’s mouth and electrodes were classified as representing the mouth region of the talker’s face (red circles; less than 5° from the center of the mouth, white dashed line) or as non-mouth (blue circles;>5°). Electrode locations of mouth (red) and non-mouth (blue) electrodes shown on posterior and medial brain views. Response enhancement (Vis-AV) for each individual electrode; inset bar graph shows mean values (±standard error). (D) In a control speech experiment, a white fixation crosshair was presented on the talker’s shoulder, moving the mouth of the talker’s face to the visual periphery. Electrodes were classified as representing the mouth of the talker (red circles; less than 5° from the the center of the mouth, white dashed line) or non-mouth (blue circles;>5°). Mouth electrodes were in the periphery of the visual field (mean eccentricity of 9.5°). Response enhancement (Vis-AV) for each individual electrode; inset bar graph shows mean values (±standard error).