What is the unit of pre-saccadic selection: A location that is spatially confined to the target of an upcoming eye movement, or an extended object – the one that an observer is aiming to inspect by directing her gaze towards it? We teamed up with Arezoo Pooresmaeili at the European Neuroscience Institute Göttingen to study how pre-saccadic attention is affected by perceptual grouping.
In a new study, now accepted for publication in Cortex, we explore if the preparation of a saccade gives rise to a spread of covert attention towards locations that, based on Gestalt principles, are likely to belong to the same object as the saccade target. While several neurophysiological studies showed, in visual cortex, attentional activation spreads across parts of the object that contains a saccade target, it remained unclear whether this effect can be observed at a behavioral level.
In two experiments (with delayed, and immediate saccade tasks), we presented four colored stimulus items containing vertically oriented gratings. Observers were instructed to saccade towards one of them indicated by the central cue. One of the three other items was perceptually grouped with the saccade target (using the Gestalt laws of color and common fate), whereas the two others formed a different perceptual group. During saccade preparation, we presented a probe (tilted grating) in the location of one of the four items and used performance in the tilt discrimination task as a measure of attentional deployment. In the immediate saccade task, we observed a substantive pre-saccadic attention shift: performance was highest at the saccade target and steadily increased towards the movement onset. Performance at the distant locations was better if that location was perceptually grouped with the saccade target. This grouping effect was prominent in the middle stages of the saccade preparation. For both immediate and delayed saccade tasks we observed a strong side effect: performance at the distant locations was higher on the same side of the stimulus configuration relative to the saccade target. These results suggest that pre-saccadic attention has an object-based component: Attention spreads along the saccade direction and towards the elements that form a perceptual group with the saccade target.
The paper is expected to appear soon in Cortex:
Shurygina, O., Pooresmaeili, A. & Rolfs, M. (2021). Pre-saccadic attention spreads to stimuli forming a perceptual group with the saccade target, Cortex, in press. [pdf]