Abstract
Being able to detect and correctly localize sudden changes in the environment is fundamental for survival. Here we examine if and how our ability to localize foveal and peripheral changes in the visual scene is modulated during the course of fixation. A central marker (fixation point) was surrounded by four identical stimuli. Stimuli, small vertical bars, could be located either all in the fovea or all in the periphery, 0.3º and 9º eccentricity, respectively, or two in the fovea and two in the periphery. Peripheral stimuli were enlarged to compensate for cortical magnification. Participants (n=5) executed a saccade toward the fixation point and at various time delays after landing, one of the stimuli briefly (50 ms) changed its orientation. Participants were required to localize the change. The degree of change in orientation was kept fixed for each stimulus throughout the experiment and it was chosen so that it yielded 80% of correct localizations when the change occurred 650 ms after saccade landing. Results show that during the course of fixation performance keeps improving for peripheral stimuli (from 38±4% at 0-250 ms to 76±3% at 750-900 ms). Performance for foveal stimuli instead increases up to 700 ms (51±4% at 0-250 ms vs 81±1% at 600-700 ms) and it drops over longer time intervals (69±4% at 750-900 ms). These trends are independent from whether participants monitor only foveal or peripheral stimuli, or both at the same time. These findings suggest that our ability to localize changes in a scene varies over the course of fixation and it is differently modulated in time for foveal and peripheral stimuli.