Sanga Cho¹ (), Jasmine Pan¹, Sam Ling¹; ¹Boston University

Our attention is involuntarily captured by sudden changes in our environment –a phenomenon known as exogenous attention. Previous studies have found that exogenous cueing of a location evokes a transient enhancement of visual processing for nearby stimuli. Although this has been well-established mostly in psychophysics and electrophysiological studies, we have relatively limited understanding of the neural mechanisms by which these effects arise. Indeed, while some neuroimaging work has found that exogenous attention boosts responses at attended locations, we lack a mechanistic account of the potential gain changes that underlie these boosted responses. Here, we examined the influence of exogenous attention on the BOLD population contrast response function (CRF) across early visual cortex (V1-V3) by pairing a contrast adaptation protocol (Vinke, Bloem & Ling, 2022) with a modified spatial cueing task. Specifically, participants began each scan with an initial adaptation period (60 sec) and each trial with top-up adaptation (4-8 sec) of two gratings (16% contrast), to promote population homogeneity in contrast response. After adaptation, participants were asked to identify the orientation of a target stimulus (200 ms), which was tilted clockwise or counterclockwise. Importantly, the target was preceded (pre-cue) or followed (post-cue) by a brief exogenous cue (50 ms). We found an increase in the gain of the contrast response with pre-cue (valid > invalid), particularly at high contrasts. This effect appeared most prominent in V1, decreasing from V2 to V3. The differential gain pattern of pre-cue was absent in post-cue trials, which rules out the possibility that the effect of the pre-cue was simply due to sensory summation by cue and target stimuli. These results suggest that exogenous attentional enhancement is regulated by response gain modulation within striate cortex, consistent with the predictions of the normalization model of attention.

Acknowledgements: R01EY028163; R01EY035640