Fig. 1.

Stimuli, procedure, and results for the behavioral TAE and orientation-selective adaptation experiments. (A) Stimuli and procedure for the TAE experiment. The adaptation procedure started with a 10-s preadaptation period. The adapting stimuli were high-contrast isoluminant R/G square wave gratings tilted 15 degrees clockwise (+) or counterclockwise (−) from the vertical orientation and counterphase flickering at 30 Hz. After the preadaptation period, a low-contrast test grating was briefly presented for 500 ms, and observers made forced-choice responses to indicate whether the test grating appeared top left-tilted or top right-tilted from the vertical orientation. Then 5-s long top-up adaptations were presented, with a 2-AFC probe test following each top-up adaptation period. (B) Psychometric functions of the perceived orientation showing significant TAE. (C) Stimuli and procedure for the orientation-selective adaptation experiment. During the preadaptation period, subjects viewed oblique (+ or −45 degrees) invisible chromatic gratings for 20 s. Then the chromatic pattern was transformed to uniform red/green flickers, and a test Gabor, either parallel or orthogonal to the adapting orientation, was briefly presented. Subjects made forced-choice responses to indicate whether the test stimulus was presented to the left or to the right of fixation. The test Gabor was presented at two oblique orientations with chromatic contrast adaptively adjusted, interleaved with 5-s top-up adaptations to the invisible gratings. (D) The contrast threshold to the probe in the same orientation as the adaptor was significantly higher compared with that in the orthogonal orientation. Error bars indicate SEM.