Figure 2.

Schematic of the general experimental paradigm. Experiment 1: While maintaining fixation on the central ring, subjects attended to either the orientation of the gratings, the contrast of the gratings, or a central letter RSVP stream. The orientation of one grating always closely matched the oriented cue line presented at fixation (randomly selected from a set of 10 orientations equally spaced across 180°); the orientation of the remaining grating either matched the other, or mismatched by a small clockwise (CW) or a counterclockwise (CCW) offset. Similarly, the contrast of one grating ranged from 65–75%, and the second grating either matched the first or mismatched by adding or subtracting a small contrast change. The subject’s task was to decide if the stimuli either matched or mismatched with respect to the relevant attended feature. Experiment 2: The display was identical to Experiment 1 (shown), with the following changes: (1) The central RSVP stream was removed, so subjects only attended to either orientation or contrast on alternating blocks of trials, and (2) The central cue was rendered in either green or red to indicate with 100% validity either a CW or CCW rotational offset in the event of an orientation-mismatch trial.