Primary Visual Cortex Activity along the Apparent-Motion Trace Reflects Illusory Perception
(A and B) Medio-posterior view on the inflated left occipital cortex of subject HP (A) and AK (B) (all six subjects are shown in Figure S3). Gray shading indicates the extension of V1 (light gray for V1) and the cortex curvature (dark gray, concave; light gray, convex). Activation maps show the cortical representation of the stimulated locations in red (motion quartet > baseline). Contrast maps in green indicate regions that are more active for vertical apparent motion than for horizontal apparent motion (ROI-based GLM at indicated locations; HP: t > 2.5, p < 0.02; AK: t > 2, p < 0.05). The dotted line is a spline-interpolated curve connecting the stimulated locations and the region that is more active during the perception of vertical apparent motion. (This line does not necessarily indicate the path of apparent motion from experiments 1 and 2 since stimulus parameters had to be adjusted.)
(C and D) The solid white lines mark regions from which event-related averages were calculated. Event-related averages are shown for subject HP (C) and for subject AK (D). The time courses are aligned to the time point at which the subject indicates a switch in perception (t = 0, black line) and are shown for the time period from 4 s before to 24 s after the perceptual switch. The first perceptual period following each stimulation onset is omitted from the analysis (see Materials and Methods). Error bars correspond to standard errors of the mean. For HP, the vertical percept lasted on average for 11.9 s (standard deviation, 10.3 s), the horizontal for 13.4 s (standard deviation, 9.2 s). For AK, the vertical lasted for 14.6 s (standard deviation, 7.1 s), and the horizontal for 16.6 s (standard deviation, 6.7 s).