Evidence for split attentional foci.

Awh, Edward; Pashler, Harold · 2000 · Journal of Experimental Psychology Human Perception & Performance

DOI: 10.1037//0096-1523.26.2.834

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Summary

This study investigates the flexibility of spatial attention, specifically testing whether observers can maintain split attentional foci on noncontiguous locations. While traditional models assume attention is allocated over contiguous regions, recent evidence suggested that attention could be divided, though previous findings were limited by strict criteria or specific stimulus conditions. The authors aimed to provide robust evidence for split attention by directly comparing processing quality at cued locations versus intervening uncued locations, and to determine the mechanisms underlying this capability. The researchers conducted a series of experiments using a partial report procedure. Observers viewed a 5 × 5 array of stimuli and were cued to attend to two noncontiguous locations where target digits or shapes were likely to appear. Cues were valid 80% of the time. On invalid trials, one target appeared in the location directly between the two cued positions, allowing for a direct comparison of attentional deployment. Experiments 1 and 1a used alphanumeric stimuli, while Experiment 2 used gap-detection tasks with rectangular shapes to rule out stimulus-specific effects. Experiment 3 introduced diagonal cue arrangements to test the influence of hemifield processing. Exposure durations were individually adjusted using a staircase procedure to ensure appropriate difficulty levels. The results consistently demonstrated a strong accuracy advantage for targets at cued locations compared to those at intervening middle locations, which in turn performed better than far unattended locations. This gradient of processing quality provided evidence for split attentional foci, even when sudden-onset distractors appeared in the intervening space. A significant interaction was found regarding cue orientation: performance was superior when cues were arranged horizontally compared to vertically. Experiment 3 revealed that this orientation effect was driven by hemifield differences; horizontal cues occupied different visual hemifields, whereas vertical cues shared a hemifield, leading to reduced performance at the bottom position due to intrahemispheric processing constraints. Finally, Experiments 4 and 4a suggested that the primary mechanism supporting flexible attentional deployment is the suppression of interference from unattended locations rather than merely enhancing processing at attended ones. The findings challenge the assumption that attention must be contiguous, providing compelling evidence that observers can effectively split attention between noncontiguous locations. The study clarifies that split attention is not an all-or-nothing phenomenon but involves a gradient of processing quality. Furthermore, it identifies hemifield-specific processing constraints and interference suppression as key factors in the deployment of spatial attention. These results refine theoretical models of attention by demonstrating that observers can maintain multiple foci simultaneously, provided they manage interference from unattended regions and account for hemispheric processing limitations.

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Topics

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• attention selective divided
• attention allocation