Abstract: PURPOSE: Previous studies have found that covert exogenous attention enhances the contrast appearance of low-contrast stimuli but attenuates the contrast appearance of high-contrast stimuli, whereas covert endogenous attention uniformly enhances the contrast appearance regardless of stimuli contrast. Here, we investigated how presaccadic attention, a kind of overt attention, alters the contrast appearance of low- and high-contrast stimuli.
METHODS: We used a central cue to direct presaccadic attention: subjects were required to saccade to the target location (saccade condition) or maintain at the center (neutral condition). Two gratings (the test and the standard) were randomly located on the left or right sides of fixation. Eye positions were monitored online and analyzed offline to extract valid trials. Subjects performed an equality judgment task, in which they reported whether two gratings are of the same or different contrast. In low-contrast condition, the contrast of standard stimulus was 22.4%, and the contrast of test stimuli systematically varied in 11 log increments from 8% to 63%. In high-contrast condition, the contrast of standard stimulus was 60%, and the contrast of test stimuli varied in 11 log increments from 37% to 97%.
RESULTS: For the low-contrast gratings, presaccadic attention enhances contrast appearance, with the average Point of Subjective Equality (PSE) in the test-cued condition lower and the average PSE in the standard-cued condition higher than the neutral. In contrast, presaccadic attention attenuates contrast appearance of high-contrast gratings, with the average PSE in the test-cued condition higher and the average PSE in the standard-cued condition lower than the neutral.
CONCLUSIONS: Our results suggest that presaccadic attention changes our subjective contrast perception by strengthening the weak stimuli but weakening the strong stimuli. This result is similar to the exogenous attention but different from the endogenous attention.

Key words: pre-saccadic attention, contrast appearance, covert attention, eye movement