Fig. 1.

Schematic of the standard procedure for plaid-selective adaptation (left) and the CAE (right). In the component field (right), individual gratings alternated every second, and in the compound field (left), the compound stimulus alternated with a blank field. Note that for convenience the component and compound stimuli are depicted as alternating at the same times. In the actual experiment, the relative temporal phase of the alternations in the two hemi-fields was given a random offset that differed every trial to avoid synchronous alternations in the two hemi-fields. For this experiment the reference probe angle was fixed and the test probe angle (compound side) was varied according to a staircase procedure to find the PSE. The probe stimuli consisted of compound stimuli. For the plaid aftereffect the test probe varied in contrast and observers judged which probe had the higher contrast. For the CAE the test probe varied in curvature and on each trial observers judged which probe stimulus appeared to have the smaller angle. Each observer performed a minimum of four staircases for each adapting configuration. Different temporal sequences were used for the compound adaptor in each experiment (see Section 2 for details).