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The pupillary light response reflects eye-movement preparation

24.17, Saturday, 17-May, 2:30 pm - 4:15 pm, Talk Room 1
Session: Eye movements: Perception and mechanisms

Sebastiaan Mathôt1, Lotje van der Linden1, Grainger Jonathan1, Françoise Vitu1`; 1Laboratoire de Psychologie, CNRS, Aix-Marseille Université

When the eyes are exposed to an increased influx of light, the pupils constrict. The pupillary light response (PLR) is traditionally believed to be purely reflexive and not susceptible to cognitive influences. In contrast to this traditional view, we report here that the PLR is initiated during the preparation of an eye movement towards a bright (or dark) stimulus, even before the eyes set in motion. Participants fixated a central gray area and made a saccadic eye movement towards a peripheral target. Using gaze-contingent display changes, we manipulated whether or not the brightness of the target was the same during and after eye-movement preparation. More specifically, on some trials we changed the brightness of the target as soon as the eyes set in motion, thus dissociating the preparatory PLR (i.e. to the target brightness during saccade preparation) from the 'regular' PLR (i.e. to the target brightness after the saccade). We show that a preparatory PLR is initiated during saccade preparation, approximately 100 ms before saccade onset. This preparatory response allows the pupil to track luminance changes in visual input more rapidly than would be possible without preparation. Strikingly, a purely preparatory luminance-related pupillary response was triggered even when a saccade was prepared towards a bright (or dark) stimulus that was removed before being brought into central vision. We link our findings to the pre-saccadic shift of attention: The pupil adjusts its size to the brightness of a to-be-fixated stimulus, as soon as attention shifts towards the target of an upcoming saccade. Our findings illustrate that the PLR is a dynamic movement that is tightly linked to visual attention and eye-movement preparation.

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