Attentional Sampling between Eye Channels

Our ability to detect targets in the environment fluctuates in time. When individuals focus attention on a single location, the ongoing temporal structure of performance fluctuates at 8 Hz. When task demands require the distribution of attention over two objects defined by their location, color or motion direction, ongoing performance fluctuates at 4 Hz per object. This suggests that distributing attention entails the division of the sampling process found for focused attention. It is unknown, however, at what stage of the processing hierarchy this sampling occurs, and whether attentional sampling depends on awareness. Here, we show that unaware selection between the two eyes leads to rhythmic sampling. We presented a display with a single central object to both eyes and manipulated the presentation of a reset event (i.e., cue) and a detection target to either both eyes (binocular) or separately to the different eyes (monocular). We assume that presenting a cue to one eye biases the selection process to content presented in that eye. Although participants were unaware of this manipulation, target detection fluctuated at 8 Hz under the binocular condition, and at 4 Hz when the right (and dominant) eye was cued. These results are consistent with recent findings reporting that competition between receptive fields leads to attentional sampling and demonstrate that this competition does not rely on aware processes. Furthermore, attentional sampling occurs at an early site of competition among monocular channels, before they are fused in the primary visual cortex.