Abstract
Pupil size changes during a visual search may reflect cognitive processes, such as effort and memory accumulation, but methodological confounds and the general lack of literature in this area leave the reliability of findings open to question. We used a novel synthesis of experimental methods and averaging techniques to explore how cognitive processing unfolds during free-viewing visual search for multiple targets. Twenty-seven participants completed 152 searches across two separate 1-hour sessions. The number of targets present (Targets: 0, 1, 2, and 3) in each trial was the main manipulation and the task was to “find all of the targets” and report the total via mouse-click at the end of the trial. Search time lasted for 10 seconds or until the participant purported to have found all of the targets, in which case they could terminate the search via keypress. Whole-trial pupil analysis revealed a significant effect of button pressing as well as a significant main effect of targets for trials that were not self-terminated via button press. Fixation-aligned pupil responses revealed transient modulations in pupil size following initial fixations on targets but not distractors and refixations on both targets and distractors. Owing to rigorous control over experimental confounds and a detailed analysis and correction of eye-movement-related measurement error, we confidently discuss these findings in terms of task-related processing and underlying brain activity.
Highlights
Pupillometry, the measurement of pupil size, has become a popular tool for researching cognitive function. Its utility for this purpose hinges to a large extent on our growing understanding of the functional association between non-luminance-mediated pupil size changes and the activity of the locus coeruleusnoradrenalin (LC-NA) system of the brain, which plays a pivotal role in the modulation of arousal, cognition, and autonomic function (Berridge, 2008; Berridge & Waterhouse, 2003; Doya, 2008; Mather & Harley, 2016; Samuels & Szabadi, 2008a, Samuels & Szabadi, 2008b; Sara, 2009; Sara & Bouret, 2012)
The average regression coefficient for X was -0.483, and for Y it was 0.009. From this it can be gleaned that pupil size was affected mostly by changes in horizontal gaze position and that rightward horizontal shifts in gaze were always associated with decreasing pupil size
Twenty-two of the 26 participants included in the analysis showed pupil responses that were greater on average for target fixations compared to distractor fixations, and at least 11 of these displayed the characteristic peak that was present in the grand-average waveform
Summary
Pupillometry, the measurement of pupil size, has become a popular tool for researching cognitive function Its utility for this purpose hinges to a large extent on our growing understanding of the functional association between non-luminance-mediated pupil size changes and the activity of the locus coeruleusnoradrenalin (LC-NA) system of the brain, which plays a pivotal role in the modulation of arousal, cognition, and autonomic function (Berridge, 2008; Berridge & Waterhouse, 2003; Doya, 2008; Mather & Harley, 2016; Samuels & Szabadi, 2008a, Samuels & Szabadi, 2008b; Sara, 2009; Sara & Bouret, 2012).
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