Abstract
This study measured the size of the attentional window when attention is narrowly focused, using attentional modulation of the pupillary light response – pupillary constriction when covertly attending a brighter than darker area. This allowed us to avoid confounds and biases involved in relying on observers’ response (e.g., RT), which contaminated previous measurements of this window. We presented letters to the right and left of fixation, each surrounded by task-irrelevant disks with varying distances. The disks were bright on one side and dark on the other. A central cue indicated which letter to attend. Luminance levels were identical across trials. We found that pupil size was modulated by the disks’ luminance when they were 1° away from the attended letter, but not when this distance was larger. This suggests that the diameter of the attentional window is at least 2°, which is twice as large as that established with behavioral measurements.
Highlights
Spatial covert attention refers to processes that prioritize information gathered from a specific location, in the absence of eye movements
If the attentional window is viewed as a round window centered at the target, our findings propose that the diameter of this window is at least 2°
This suggests that the minimal size of the attentional window is twice as large as that found with behavioral measurements[6]
Summary
Spatial covert attention refers to processes that prioritize information gathered from a specific location, in the absence of eye movements. Behavioral measurements could be affected by various factors that are not directly related to the size of the attentional window, such as higher-level strategies, decisional criteria, experience, learning, speed accuracy tradeoffs, response biases, etc. This is so with RT, as it involves factors related to motor preparation. Once the irrelevant stimuli appear at a distance larger than the attentional window, their luminance should not affect pupil size. This allowed us to estimate the size of the attentional window.
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