Changes in attentional breadth scale with the demands of Kanizsa-figure object completion-evidence from pupillometry

Abstract

The present study investigated whether the integration of separate parts into a whole-object representation varies with the amount of available attentional resources. To this end, two experiments were performed, which required observers to maintain central fixation while searching in peripheral vision for a target 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. Experiment 1 revealed a performance benefit for grouped (relative to ungrouped) targets, which increased with decreasing distance from fixation. By contrast, search for ungrouped targets was comparably poor in accuracy without revealing any eccentricity-dependent variation. Moreover, measures of pupillary dilation mirrored this eccentricity-dependent advantage in localizing grouped targets. Next, in Experiment 2, an additional attention-demanding foveal task was introduced in order to further reduce the availability of attentional resources for the peripheral detection task. This additional task hampered performance overall, alongside with corresponding pupil size changes. However, there was still a substantial benefit for grouped over ungrouped targets in both the behavioral and the pupillometric data. This shows that perceptual grouping scales with the allocation of attention even when only residual attentional resources are available to trigger the representation of a complete (target) object, thus illustrating that object completion operates in the "near absence" of attention.

Keywords: Attentional breath; Covert attention; Object integration; Perceptual grouping; Pupillometry; Visual attention.

Fig. 1

Illustrations of the grouped (A) and ungrouped (B) targets and the distractor configurations (C), as presented in the experiments. Panel (D) depicts an example trial sequence in Experiment 1. A premask display presented six filled placeholder circles for 250 ms, which was followed by a blank screen for 200 ms. Next, the search display appeared and remained on the screen for 300 ms, either presenting a grouped (left) or an ungrouped (right) target (in the example depicted, both targets are presented at an eccentricity of 10º). (E) In Experiment 2, the trial sequence was the same, except that an additional, foveal task was added to the search display, which required a line length discrimination of the (vertically or horizontally stretched) fixation cross

Fig. 2

Mean accuracies (% correct), with within-subject 95% confidence intervals, for grouped (left) and ungrouped (right) targets as a function of target eccentricity

Fig. 3

(A) Time courses of the pupil-size deviation from baseline, in arbitrary units, for varying target eccentricities (of 5°, 10°, and 15°), separately for grouped (left) and ungrouped (right) target configurations. The dashed vertical lines denote the sequence of display frames on a given trial (fixation, premask, blank, search display, and dilation period, respectively). (B) Mean pupil size deviations from baseline (with corresponding within-subject 95% confidence intervals) for grouped (left) and ungrouped (right) targets as a function of target eccentricity, as measured in the dilation period (the gray shaded area in the figures in panel A). Note that the subtraction procedure used to calculate mean pupil-size deviations yielded negative values, where a larger negative deviation corresponds to a smaller pupil size (thus reflecting a comparably narrow attentional focus)

Fig. 4

Time courses of the pupil-size deviation from baseline (in arbitrary units) during the dilation period at varying target eccentricities (of 5°, 10°, and 15°), for grouped (top) and ungrouped (bottom) target configurations

Fig. 5

Results in the peripheral search task in Experiment 2 (given correct performance in the foveal task under dual-task conditions). (A) Mean accuracies (% correct) and (B) mean pupil size measures (with corresponding 95% within-subject confidence intervals) for grouped and ungrouped targets as a function of task. Pupil size measures depict the deviations from baseline as measured in the dilation period. (C) Time courses of the pupil-size deviation from baseline, in arbitrary units, in the single- and dual task conditions for grouped (left) and ungrouped (right) target configurations. The dashed vertical lines denote the sequence of display frames on a given trial (fixation, premask, blank, search display, and dilation period, respectively). Note that the use of a subtraction procedure to calculate mean pupil deviations resulted in negative values, with a larger negative deviation corresponding to a smaller pupil size (thus reflecting a comparably narrow focus of attention)

Fig. 6

Time courses of the pupil-size deviation from baseline (in arbitrary units) during the dilation period, in the single- and dual task conditions for grouped (top) and ungrouped (bottom) target configurations