Abstract
[Goal] Orienting covert exogenous spatial attention to a target location improves visual performance in many visual tasks. The role of early visual cortical areas in such effects is largely unknown. Here, to establish a causal link between these visual areas and task performance, we used transcranial magnetic stimulation (TMS) to briefly disrupt cortical activity and determine whether early visual areas mediate the effect of exogenous attention on performance. [Methods] First, observers underwent TMS stimulation near the left occipital pole and drew the location of their perceived phosphene. Second, they performed an orientation discrimination task. Following a peripheral valid, neutral, or invalid cue, two cortically magnified gratings were presented, one in the phosphene region and the other in the symmetric region in the opposite hemifield. Observers received double pulse TMS while the stimuli were presented. Shortly after, a response cue indicated the target stimulus. Thus, 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 and TMS conditions. [Results] Performance in the neutral condition was similar under both stimulation conditions. When the distractor was stimulated, as expected, exogenous attention yielded response gain: performance benefits at the high contrast levels in the valid-cue condition and costs in the invalid-cue condition compared to the neutral condition. In contrast, when the target was stimulated, the contrast response functions were similar; there was neither a benefit at the valid-cued location nor a cost at the invalid-cued location. [Conclusions] TMS eliminated both the benefits of exogenous attention at the attended location and costs at the unattended location. These results establish a causal link between early visual areas and the modulatory effect of exogenous attention on performance.