Pilots face the problem of attentional selectivity, when one needs to stay focused on the current task while being attentive to other inputs, whether or not they are task-relevant. In this study we evaluate the influence of cognitive load on attentional resources available to process auditory distractors, while performing a visual task. Such cross-modal auditory-visual interference is of a particular interest in the aeronautics, as focal-task is often visual (flight deck instruments, outside) while background auditory inputs are numerous (alarms, radio, cabin-crew communications etc.). In this paper we adapted an auditory-visual interference paradigm to a simple visual piloting task. Sixteen volunteers performed both low and high load conditions while their left pupil size was continuously recorded. As shown by statistical analyses, the tonic pupil diameter was higher for high load condition accompanied with performance degradation. Therefore, the pupil diameter successfully tracked the memory load level, measured objectively with targeting accuracy and subjectively with NASA-TLX questionnaire. As also revealed by statistical analyses, the pupillary reaction reflected the processing load of irrelevant auditory stimuli. In particular, as for low load condition, the incongruent auditory stimuli evoked larger pupillary response compared to the congruent distractor, showing higher effort for resolving the conflict of auditory-visual interference. No such interference effects were found under high load condition. As indicated by tonic pupil diameter and task-evoked response, for high load condition participants run out of cognitive resources to process auditory distractors. These results are in line with the hypothesis that vision and hearing share a common pool of resources, and that attentional capture of irrelevant stimuli is impaired under increased load on working memory.
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