Cristina de la Malla¹, Martina Poletti^2,3,4; ¹Vision and Control of Action (VISCA) Group, Department of Cognition, Development and Psychology of Education, Institut de Neurociències, Universitat de Barcelona, Barcelona, Catalonia, Spain, ²Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA, ³Department of Neuroscience, University of Rochester, Rochester, NY, USA, ⁴Center for Visual Science, University of Rochester, Rochester, NY, USA

Although fixation is normally considered as a temporal unit, humans’ ability to localize changes in a scene varies over the course of brief fixation periods, and it is differently modulated in time for foveal and peripheral stimuli. While change localization accuracy for peripheral stimuli improves with time after saccade landing, it remains relatively stable for foveal stimuli. Here we examine whether the degree of improvement increases as a function of eccentricity (0.3º, 2º, 6º, or 15º; fovea to periphery). A fixation point was surrounded by four bars presented either all at the same eccentricity, or split between two eccentricities. Stimuli were enlarged as a function of eccentricity to compensate for cortical magnification. Participants (n=10) executed a saccade toward the fixation point, and at random time delays after saccade landing (up to 450 ms), one of the bars briefly (50 ms) changed its orientation. Participants were required to indicate which of the bars moved. The degree of orientation change was kept fixed for each stimulus location throughout the experiment to yield 71% of correct localizations when the change occurred ~200 ms after saccade landing independently of stimulus eccentricity. Results show that localization performance improved over time during the course of fixation, with larger improvements at greater eccentricities (9.6%, 8.6%, 14.0% and 21.8% increases for smaller to larger eccentricities). When stimuli were presented at two different eccentricities, performance was higher for the stimuli closer to the center of gaze early on during fixation. As fixation time progressed, performance for both near and far stimuli improved following a similar pattern to that observed when each eccentricity was tested in isolation. These results indicate that monitoring stimuli across eccentricities leads to an initial cost for the more eccentric stimuli, in part compensated by a quick recovery over the course of fixation.

Acknowledgements: This work is funded by grant PID2023-150883NB-I00 from the MCIN/AEI/10.13039/501100011033 to CM and NIH Grant EY029788 to MP.