Abstract
Similar to a camera aperture, pupil size adjusts to the surrounding luminance. Unlike a camera, pupil size is additionally modulated both by stimulus properties and by cognitive processes, including attention and arousal, though the interdependence of these factors is unclear. We hypothesized that different stimulus properties interact to jointly modulate pupil size while remaining independent from the impact of arousal. We measured pupil responses from human observers to equiluminant stimuli during a demanding rapid serial visual presentation (RSVP) task at fixation, and tested how response amplitude depends on contrast, spatial frequency, and reward level. We found that under constant luminance, unattended stimuli evoke responses that are separable from changes caused by general arousal or attention. We further uncovered a double-dissociation between task-related responses and stimulus-evoked responses, suggesting that different sources of pupil size modulation are independent of one another. Our results shed light on neural pathways underlying pupillary response.
Significance Statement
Pupils respond characteristically to various modulating factors. Even when the overall luminance remains constant, pupil-size reflects changes in low-level stimuli and arousal. However, it is currently unclear how different factors modulating pupil size interact with each other. In this study, we show an interaction between contrast and spatial frequency on pupil size modulation while remaining independent of arousal effects. Our findings highlight the need to delineate task-related responses from stimulus-evoked responses present in stimulus trials.
Footnotes
Authors report no conflict of interest
This research was supported by the Intramural Research Program of the NIH (ZIAMH0029066), under National Institute of Mental Health Clinical Study Protocol 93-M-1070 (NCT00001360).
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
