A linear cue combination framework for understanding selective attention

Abstract

We can base visual judgements on selected parts of a scene, and ignore other parts. This ability is called selective visual attention. Sometimes selective attention is imperfect, which raises the question of how attended and unattended stimulus elements together determine observers' responses, and the related question of how to measure intermediate degrees of selective attention. Using a linear cue combination framework, we develop a measure of selective attention, *attentional weight*, that describes the relative weight observers assign to attended and unattended stimulus elements. We describe a method for measuring attentional weight by measuring the correlation between the strength of attended and unattended elements and observers' responses. We use this method to test whether observers can direct selective attention according to contrast polarity when judging global direction of motion or global orientation. We find that when observers try to judge the global direction or orientation of black or white stimulus elements, their responses are influenced by elements of the opposite contrast polarity. The attentional weight assigned to opposite-polarity distractors is typically 65% of the weight assigned to targets in the motion task, and 25% in the orientation task. Thus observers have only a limited ability to direct attention according to contrast polarity. Finally, we test a key assumption of the cue combination approach, namely that selectivity is the same for attended and unattended elements, and that observers simply assign less weight to unattended elements. We do this by using reverse correlation to measure directional selectivity for attended and unattended motion signals in random dot cinematograms. We find that selectivity is the same for both, namely a sinusoidal function of direction. We conclude that selective attention operates by modulating the weight assigned to unattended stimulus elements, without changing selectivity for unattended elements.