Abstract
[Background] Shortly before a saccade, attention shifts to the upcoming fixation, improving visual sensitivity already before the eyes move. Some behavioral and neural correlates of “presaccadic attention” are similar to those of covert exogenous attention – which likewise automatically enhances sensitivity, but during fixation. Although presaccadic and covert exogenous attention are dissociable, this similarity has led to the debatable notion that the two processes are functionally equivalent and rely on the same neural circuitry. [Method] Participants received TMS near the occipital pole and marked their perceived phosphene. Subsequently, they performed saccades to their phosphene region or the mirrored location in the opposite hemifield and discriminated an oriented grating presented shortly before saccade onset either at or opposite to the saccade target. We applied double pulse sub-threshold occipital (V1/V2) or frontal (rFEF+) TMS at different times during saccade preparation. [Results] V1/V2 stimulation reduced the presaccadic sensitivity benefit at the saccade target only during the last 100 ms before saccade onset (the peak of presaccadic attention). In contrast, rFEF+ stimulation did not affect sensitivity at the saccade target, but enhanced it at the opposite location, where presaccadic sensitivity is known to be severely reduced. [Conclusion] This demonstrates a causal – and differential – role of occipital and frontal-oculomotor areas in presaccadic benefits (at the saccade target) and costs (elsewhere). Whereas V1/V2 TMS has been shown to extinguish covert exogenous attention at a fixed delay once it has been deployed (100-150 ms after the attention cue), for presaccadic attention the effect of V1/V2 stimulation was specifically locked to the period right before saccade onset – indicating that occipital regions are recruited during later stages of saccade programming. These results are consistent with presaccadic attention modulating perception through feedback from oculomotor structures to occipital cortex, and provide further evidence dissociating presaccadic and covert attention.