Nihan Alp¹ (), Zeynep Karagül¹, Bilge Sayim²; ¹Sabanci University, Istanbul, ²École Normale Supérieure (ENS), PSL University, CNRS

Peripheral vision differs from foveal vision in several respects, including a reduction in spatial resolution with increasing eccentricity, and different temporal processing. Recently, we found that the ability to discriminate the synchrony of two dynamic faces —one presented at the fovea and the other in the periphery— declined with increasing eccentricity. Interestingly, this decline was nonlinear: Performance was relatively stable at small eccentricities, and declined sharply at eccentricities larger than 6°. However, it remains unclear whether this decline is driven primarily by characteristics of peripheral vision, such as reduced spatial resolution and increased crowding—or by an increasing difference between features extracted in the fovea versus the periphery. Here, we addressed this question by investigating how foveal blur affects the perceived temporal synchrony between two faces, one presented foveally and the other peripherally (at 6° or 12°). By systematically varying the blur of the foveal face, we aimed to manipulate the similarity between foveal and peripheral inputs. The peripheral face was always unblurred. The foveal face was presented with one of four Gaussian blur levels (σ = 0, 20, 40, 60; hereafter blur0–blur60). Participants indicated whether the two face videos were synchronous or asynchronous. Participants’ sensitivity at 6° was higher than at 12° across all blur levels, with a gradual decrease of the difference with increasing blur. At 6°, there was a gradual decline with increasing blur, followed by a steep decline at the highest blur level. At 12°, by contrast, sensitivity did not differ between moderate blur levels (blur0 to blur40), and there was a steep decline at the highest blur level. Taken together, our results indicate that synchrony perception depends not only on stimulus properties, but also on the location of stimuli in the visual field which shapes their perceived similarity.

Acknowledgements: N.A and Z. K. are supported by the Scientific and Technological Research Council of Turkey (TUBITAK 1001) under the Grant Number 122K922.