Rhythmicity in proactive and retroactive attention

Attention plays a key role in sampling relevant perceptual representations of the environment. The sampling seems rhythmic, manifested in fluctuations of behavioral performance. In previous research however, this rhythmic sampling has been limited to proactive attention (attending to upcoming events). The temporal dynamics of retroactive attention (attending to past events) remains unknown. Here, we investigate whether attention enhances perceptual processing in a rhythmic manner, both proactively and retroactively. We used an exogenous attention paradigm, where a cue drew attention to one of two possible target locations, either before or after the target onset. The cue was uninformative, resulting in half congruent trials and half incongruent trials, to minimize the attentional effect on post-perceptual decisions. The contrast of the target, a Gabor patch, was individually thresholded so that it was visible in approximately 50% of trials. Participants discriminated orientation and rated their awareness of the target. We found that the attentional enhancement of perception waxed and waned at a theta frequency depending on the cue-target interval, consistent with previous findings. Importantly, rhythmic behavior was not only observed in trials where the cue preceded the target but also when the cue followed the target, suggesting rhythmic properties of retroactive attention. Further, the behavioral rhythms at the cued and uncued locations were in antiphase. These space-based temporal dynamics were present regardless of target visibility. Note that all the above findings were significant at an individual level. Together, these findings suggest that attention is intrinsically rhythmic regardless of pro- or retroactive allocation.