Spatial biases of covert attention with dynamic gaze position

Humans express multiple biases in the spatial distribution of attention. While overt attention tends to center on visual content, or show a slight bias to the left, it is still largely unknown whether covert attention (attention shifts without eye movements) also exhibits spatial biases similarly to those of overt attention. The current study assesses the spatial biases of covert attention with two experiments. In Experiment 1, participants overtly tracked a moving dot and covertly discriminated probes surrounding it. Discrimination performance was higher for probes presented at the screen center independent of gaze locations, indicating that covert attention expresses a spatiotopic center biases similar to that of overt attention. Moreover, when the gaze was on the left, performance was enhanced towards the screen center, relative to the gaze position, indicating that covert attention also exhibits a retinotopic bias towards the center when overt attention is leftward. Experiment 2 assessed the distribution of covert attention during free-viewing movies, indexing covert attention via pupillary light responses. The results replicated Experiment 1 by showing a similar retinotopic center bias of covert attention when overt attention was leftward but not rightward. Together, the results imply that covert attention bias depends on the allocation of overt attention which is often leftward and may serve to compensate for the hemispace unattended by overt attention.