Abstract
Most studies of inattentional blindness — the failure to notice an unexpected object when attention is focused elsewhere — are limited to one critical trial. Noticing of the unexpected object on that trial could be due to random variability, such that any given individual is equally likely to notice the unexpected object. Or, individual differences in the ability to perform the primary task might make noticing more likely for some individuals than others. Increasing the difficulty of the primary task does decrease noticing rates with brief static displays and visual search arrays (Cartwright-Finch & Lavie, 2007) as well as with dynamic monitoring tasks (Simons & Chabris, 1999). However, those studies did not explore whether individual differences in noticing arise from differences in the ability to perform the primary task. We used a staircase procedure to equate primary task performance across individuals in a dynamic inattentional blindness task (Most et al, 2000) at either 60% accuracy (faster motion) or 90% accuracy (slower motion) and found that subsequent noticing was substantially greater with the 90% threshold. Thus, load of the primary task affected noticing rates when individual differences in the ability to perform the task were effectively eliminated. A second study determined the speed at which each observer could perform the primary task with 75% accuracy and showed that individual differences in that speed did not predict noticing of an unexpected object in a subsequent set of trials. Together, these findings suggest that the demands of the primary task affect inattentional blindness rates, but that individual differences in the ability to meet those demands do not.