Yue Guzhang¹, Alessandro Benedetto², Martina Poletti¹; ¹University of Rochester, ²University of Florence

Previous work demonstrated that covert attention can be selectively directed within the 1-deg foveola, enhancing fine spatial vision. The N2pc component, a well-known EEG marker of covert attention, has been extensively studied extrafoveally using large stimuli spanning >1-deg of visual angle. Investigating the N2pc component when attention is selectively shifted within the foveola between stimuli close to the resolution limit is challenging due to difficulties in maintaining precise stimulus lateralization in the presence of constant fixational eye movements. Here, we circumvented these challenges and examined whether the N2pc component is associated with selective attention shifts within the foveola when observers focus on fine spatial detail. Participants (N = 11) were instructed to attend to either a red or green stimulus. The color assignment was counterbalanced across blocks. While maintaining central fixation, a red and a green square (0.12° in size) were briefly presented 0.33° to the left and right of fixation. One square had a small gap positioned either at the top or bottom. Participants reported the gap location as quickly and accurately as possible. In informative blocks, the gap appeared in the cued stimulus, whereas in uninformative blocks, it appeared randomly between the two stimuli. Leveraging high-precision eye-tracking and retinal stabilization, we ensured that the stimuli remained at the same retinal location throughout each trial. Participants discriminated high-acuity stimuli more accurately (p=0.0467) and responded faster (p=0.0019) in informative than uninformative trials, confirming that selective attention was engaged. Additionally, a clear N2pc component was observed in both types of trials. Yet, its amplitude was larger in informative trials (-2.05µV±1.34µV vs. -0.80µV±0.87µV, p = 0.0064). These findings show that even fine-grain visual attention shifts within the foveola can reliably elicit an N2pc, with amplitude varying based on the attentional focus.

Acknowledgements: NIH R01 EY029788-01 and Sloan Fellowship