Have a Look - the Role of Covert Attention Shifts for Object Integration: Evidence from Pupillometry.

The present study investigated whether the integration of separate parts into a whole-object representation requires attention to be allocated at the location of an object. To this end, two experiments were performed, which required observers to maintain central fixation while searching for a target configuration in peripheral vision among various distractor configurations. The target could either be a “grouped” whole-object Kanizsa figure, or an “ungrouped” configuration of identical figural parts, but which do not support object completion processes to the same extent. In the experiments, accuracies and changes in pupil size were assessed, with the latter reflecting a marker of the covert allocation of attention in the periphery. The results in Experiment 1 revealed a performance benefit for grouped (relative to ungrouped) targets, which increased with decreasing distance from fixation. Moreover measures of pupillary dilation mirrored this eccentricity-dependent advantage for the localization of grouped targets. Next, to further probe the coupling between attention and grouping, in Experiment 2, an additional attention-demanding central task was introduced. This additional task hampered performance overall, alongside with corresponding pupil size changes, thus showing that attention was bound to the central task. However, there was still a substantial benefit for grouped over ungrouped targets in both the behavioral and the pupillometric data. This suggests that initial perceptual grouping operates independently from the allocation of covert attention, but pupil size changes also appear to reflect the subsequent (attention-dependent) comparison of a grouped target with a corresponding target template.