What do the inattentionally blind see? Evidence from 10,000 subjects

Inattentional blindness (IB) – the failure to notice perfectly visible stimuli when attention is otherwise engaged – has fascinated vision scientists for nearly half a century. A key reason is that IB is thought to illuminate the relationship between attention and awareness, seemingly revealing that visual consciousness requires attention. In drawing such conclusions, a crucial assumption is that subjects who report not noticing an unexpected stimulus are truly unaware of it. In four experiments, involving >10,000 participants, we found that subjects who report not noticing an unexpected stimulus can still answer questions about it at above-chance levels, casting doubt on this assumption. Exps.1-3 tested brief-duration IB: On trials 1-3, a cross briefly appeared, and subjects reported which arm was longer. On trial 4, some subjects were shown an unexpected colored line on one side of the display; others were shown nothing additional. Exp.4 tested sustained IB: Subjects counted how often squares of one color bounced off the display’s perimeter, while ignoring squares of another color. During this task, some subjects were shown either a circle or triangle traversing the display for 5s. In all experiments, regardless of whether something unexpected appeared, each subject answered the traditional IB question (“Did you notice anything unusual?” yes/no), followed by other discrimination questions (e.g., “Was the extra line red or blue?”). Exps.1-4 revealed significant sensitivity to location (Exps.1&3), color (Exps.2&4) and shape (Exps.2&4), even amongst non-noticing subjects. Moreover, subjects were biased to report not noticing, suggesting greater awareness than is revealed by yes/no questioning. Indeed, Exp.3 found (a) that even highly confident non-noticers performed above chance on location discrimination, and (b) that yes/no confidence predicted discrimination accuracy, suggesting that subjects have graded access to information about unexpected stimuli. Together, these data are consistent with the hypothesis that inattention degrades but does not abolish awareness.