Figure 1.

Illustration of stimuli and task procedures. (a) For face detection, subjects indicated on which side, the left or the right, a line-drawn face embedded within a larger drawing was located. Images were presented briefly (13–104 ms). (b) For contrast detection, subjects indicated which of two time intervals contained a sinusoidal grating on the computer screen. Gratings were either temporally modulated or static, with varying spatial and temporal frequencies.