Primary Visual Cortex Activity along the Apparent-Motion Trace Reflects Illusory Perception
Medio-posterior view on the inflated left occipital cortex of subject HP (A and B) and subject AK (C). All five subjects are shown in Figure S1. Gray-scale coloring of cortex indicates the extent of retinotopic visual areas (light gray: V1 and V3/VP; dark gray: V2, V4, and V3A) and the gyral pattern (concave surfaces are indicated in darker gray in the respective areas).
(A) The cortical representations of the mapping stimuli are marked in color. The maps were obtained by calculating a balanced contrast between the respective mapping condition of interest and the two other mapping conditions (e.g., middle versus upper and lower). The thresholds of t-maps were individually adjusted to obtain patches of comparable size in V1: upper (yellow), t(600) > 9.3; middle (orange), t(600) > 11.9; and lower (red), t(600) > 15.1 (all p << 0.001).
(B) Cortical activation maps for the apparent-motion (green) and real-motion (blue) condition compared to baseline (apparent motion in V1: t > 3.6, p < 0.0004; real motion in V1: t > 18.6, p << 0.001). Cortical representations of the mapping stimuli are indicated by colored outlines taken from (A). The solid white line indicates a patch of significant activation (t > 3, p < 0.003) for the following conjunction of contrasts, which represents the ideal activation pattern: (middle > upper) and (middle > lower) and (apparent motion > upper) and (apparent motion > lower). The dashed white line marks a peripheral region in V1 with significant activation in response to apparent motion and real motion.
(C) Same as (B) for subject AK. The white region with the optimal response pattern overlaps largely with the representation of the middle stimulus (in orange; see Figure S1 for details).
(D) Event-related BOLD signal change for subject HP plotted over time from the patch outlined by the solid white line in (B) (solid black line indicates stimulus onset, dotted line stimulus offset).
(E) Event-related BOLD signal change of the apparent-motion-activated (green) region from the eccentric parts of V1 outlined by the dashed white line in (B) (solid black line indicates stimulus onset, dotted line stimulus offset). This eccentric region responds to real motion and apparent motion but not to the middle stimulus.
(F) Same as (D) for subject AK.
Error bars correspond to standard errors of the mean.