Abstract
Goal: Orienting covert endogenous spatial attention to a target location improves performance in many visual tasks. The human homologue right frontal eye-field (rFEF) has been implicated in attentional selection, but the causal role of this region on task performance and contrast sensitivity remains unknown. Here, we used transcranial magnetic stimulation (TMS) to briefly disrupt cortical activity while observers performed a contrast sensitivity task to establish a causal link between rFEF and attentional modulation. Methods: Following a peripheral cue that indicated the to be attended location (75% valid), two oriented gratings were presented on the horizontal meridian, one in each hemifield. Observers received double pulse TMS on the rFEF (localized using an atlas parcellation and validated via the junction of the precentral and superior frontal sulcus) during stimulus presentation. Shortly after, a response cue indicated which grating’s orientation had to be discriminated. Importantly, the response cue either matched (target stimulated) or did not match (distractor stimulated) the stimulated side. Grating contrast was manipulated to measure contrast response functions for all combinations of attention (valid, neutral, invalid) and TMS conditions (target or distractor stimulated). Results: In the distractor stimulated condition we observed the typical effects of attention on contrast sensitivity; benefits with the valid cue and costs with the invalid cue. In the target stimulated condition, contrary to our previous results stimulating early visual areas (Fernández & Carrasco, SFN 2021), TMS to rFEF significantly weakened endogenous attentional effects (indexed by valid minus invalid performance). Conclusions: Our results establish a causal link between the known effects of endogenous attention on contrast sensitivity and rFEF. Taken together with our previous findings, the rFEF is causally linked to endogenous attentional modulations whereas early visual areas are not. Instead, early visual areas are necessary for exogenous attention (Fernández & Carrasco, 2020)—creating a double dissociation.