Figure 1.

Experimental sequence: Each block began with an initial adaptation phase, during which the participant fixated while viewing a display of the two side-by-side adapting patches for 1 minute. After this initial adaptation, each trial consisted of a top-up adapting display presented for 2 seconds (to ensure participants remained adapted to the two mean sizes), followed by a test display of two single dots, which remained on the screen until the participant reached to the pre-specified test dot. Once the participant touched the screen to grasp the test dot, a 500 Hz tone sounded for 200 ms as the screen blanked except for the fixation cross, signaling the participant to make a keypress response to the perceptual comparison task. The screen remained blank until the keypress response, or for 3 seconds, whichever came first. Two consecutive trials are shown above to clarify that there was only a single 1-minute initial adaptation display at the start of each block followed by multiple 2-second top-up displays, as well as to illustrate that although the mean size of the adapting dots was held constant over the course of each block, the dots were arranged in random positions within each presentation of the adapting and test displays.