Figure 2.

Schematic of the general experimental paradigm. Experiment 1, While maintaining fixation on the central ring, subjects attended to 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 matched the other or was mismatched by a small CW or a CCW offset. Similarly, the contrast of one grating ranged from 65 to 75%, and the second grating matched the first or mismatched by adding or subtracting a small contrast change. The subject's task was to decide if the stimuli 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 orientation or contrast on alternating blocks of trials and (2) the central cue was rendered in green or red to indicate with 100% validity either a CW or CCW rotational offset in the event of an orientation-mismatch trial.