Pre-saccadic shifts of attention are independent of stimulus eccentricity

Humans often explore the visual environment through saccades, bringing relevant visual stimuli to the center of gaze. During saccade programming, visual attention is directed to the location where the eyes will move to, enhancing the perception of visual stimuli presented at the saccade target. Recent studies have suggested that rather than being uniformly distributed in space, there are some important asymmetries in how these pre-saccadic shifts of attention modulate perception across the visual field. This study investigates the effects of pre-saccadic attentional shifts to stimuli at different eccentricities during a psychophysical discrimination task. Sixteen human participants were instructed to fixate at the center of the screen while dynamic 1/f noise stimuli (50 ms refresh rate) were presented at 4, 5.76, 8.32, and 12 degrees of visual angle (dva), in separate blocks of trials. The stimuli sizes were scaled by the magnification factor (1.7, 2.09, 2.65, 3.47 dva respectively). After a random fixation period, a central cue (line with 0.4 dva) was presented for 75 ms indicating the saccade direction. A visual target (1/f noise filtered at 45º or 135º) was randomly presented on either side of the screen 140 ms after the cue onset (i.e., during saccade preparation). Participants had to discriminate the target’s tilt (clockwise or counterclockwise), while its contrasts were adjusted using a staircase procedure. We found that saccade preparation improved contrast sensitivity in all tested eccentricities. Because eccentricity and saccade amplitude are always coupled in our study, our results show that the amount of pre-saccadic perceptual modulation is independent of the size of the saccade being prepared.