Pupillary response predicts multiple object tracking load, error rate, and conscientiousness, but not inattentional blindness

• Observers' pupil size as an index of effort was recorded during a tracking task.
• Pupillary response predicted task load, errors, and conscientiousness.
• Pupillary response failed to predict inattentional blindness (IB).
• Covert pupil measures were more sensitive measures than overt behavior (errors).
• Effort recruited to complete the primary task appears unrelated to IB.

Research on inattentional blindness (IB) has uncovered few individual difference measures that predict failures to detect an unexpected event. Notably, no clear relationship exists between primary task performance and IB. This is perplexing as better task performance is typically associated with increased effort and should result in fewer spare resources to process the unexpected event. We utilized a psychophysiological measure of effort (pupillary response) to explore whether differences in effort devoted to the primary task (multiple object tracking) are related to IB. Pupillary response was sensitive to tracking load and differences in primary task error rates. Furthermore, pupillary response was a better predictor of conscientiousness than primary task errors; errors were uncorrelated with conscientiousness. Despite being sensitive to task load, individual differences in performance and conscientiousness, pupillary response did not distinguish between those who noticed the unexpected event and those who did not. Results provide converging evidence that effort and primary task engagement may be unrelated to IB.