Influential inattentional blindness paradigms and their results.

(Left) In a representative study from Mack & Rock (1998), subjects fixated in the center of the circle and reported which arm of a centrally presented cross was longer. On the critical trial, an unexpected shape appeared in the near periphery at the same time as the cross and subjects were asked whether they noticed anything unusual. (Center) In Simons & Chabris (1999), subjects counted the number of basketball passes made by individuals wearing white shirts. (Images drawn from Simons and Chabris, 1999, reprinted with permission Dan Simons.) On the critical trial, a woman in a gorilla suit paraded through the display for five seconds, and subjects were asked whether they noticed anything unusual. (Right) In Wood & Simons (2017; based on Most et al., 2001), subjects fixated on the blue square and reported the number of times the white or checkerboard squares bounced off the walls of the display. On the critical trial, a black circle entered from the right and crossed the display for several seconds, and subjects were asked whether they noticed anything unusual. In all three experiments (and many others in this literature), a considerable proportion of subjects reported not noticing these unexpected stimuli.

Stimuli, procedure and results for Experiment 1.

a Schematic trial sequence for Experiment 1. On trials 1-3 subjects were presented with a cross above or below fixation for 200 msec and judged which arm was longer. On trial 4, an unexpected red line appeared in the periphery simultaneous with the cross. After reporting which cross-arm was longer, subjects were asked, “Did you notice anything unusual on the last trial that wasn’t there on previous trials?” (yes/no), followed by a 2afc question concerning the location of the line (left/right). b Percentage of subjects who report noticing or not noticing the extra red line. 29% of subjects were ‘non-noticers’. c Performance on the 2afc question (left/right location of the line), considering only those subjects who reported not noticing anything unusual. Remarkably, both %-correct and d′ were significantly above chance among these subjects who met traditional criteria for inattentional blindness. In other words, subjects who answered “no” demonstrated sensitivity to the location of the stimulus they had just claimed not to have noticed. Error bars are 95% CIs.

Stimuli, procedure and results for Experiments 2 and 3.

a Schematic trial sequence for Experiment 2. On trials 1-3 subjects were presented with a cross above or below fixation for 200 msec and judged which arm was longer. On trial 4, for 2/3rds of subjects, an unexpected line appeared in the periphery simultaneous with the cross. This line could be either blue or red and one the left or right. For 1/3 of subjects no additional line was shown. After reporting which cross-arm was longer, all subjects were asked, “Did you notice anything unusual on the last trial that wasn’t there on previous trials?” (yes/no), followed by a one-interval forced-response question concerning the color of the line (red/blue). b Performance on the one-interval forced-response question about the unexpected line’s color amongst subjects who were shown a line and who reported not noticing anything unusual (27.73% of subjects). Subjects who answered “no” demonstrated sensitivity to the color of the stimulus they had just claimed not to have noticed. c Schematic trial sequence for Experiment 3. Trials 1-4 were identical to Experiment 1, except subjects were asked additional questions about their confidence following both yes/no and 2afc questions. d Performance on the 2afc question in Experiment 3, considering only subjects who reported not noticing anything unusual (30.85% of subjects). Replicating the finding of Experiment 1, subjects who answered “no” demonstrated sensitivity to the location of the stimulus they had just claimed not to have noticed. e Performance on the 2afc question in Experiment 3 for all subjects, broken down by confidence in their response to the yes/no question whether they had noticed anything unusual. Remarkably, even subjects who were highly confident that they had not noticed anything unusual were significantly above chance. Error bars are 95% CIs.

Stimuli, procedure and results for Experiment 5.

a Stimulus parameters and a schematic critical trial for Experiment 5, in which an unexpected object moved across the display for several seconds while subjects counted the number of times the white squares bounced off the display’s ‘walls’ (task adapted from Wood & Simons, 2017). The unexpected object varied in its shape, color, direction of motion, and side of the display. As in Experiment 4, subjects were then asked follow-questions about this stimulus’s color, shape and location. b Subjects who reported not noticing the unexpected stimulus still showed above-chance sensitivity to its color and shape (though not to its location), a pattern predicted in our pre-registration. Thus, sensitivity to IB stimuli arises even when the stimuli are visible for a sustained period (rather than appearing only briefly, as in Experiment 1-3). Error bars are 95% CIs.

Conservative criteria in Experiments 2, 4 and 5.

a Critical trials from Experiments 2, 4 and 5, showing present trials in which an IB stimulus was presented to subjects (2/3rds subjects in Experiment 2, 3/4 in Experiments 4 and 5), and absent trials in which no IB stimulus was presented (1/3rd subjects in Experiment 2, 1/4 in Experiments 4 and 5). On all trials, subjects were asked, “Did you notice anything unusual on the last trial that wasn’t there on previous trials?” (yes/no). b Left: Decision matrix for this yes/no question, indicating the four possible stimulus/response pairings: hits corresponding to ‘yes’ responses on present trials; false alarms corresponding to ‘yes’ responses on absent trials; misses corresponding to ‘no’ responses on present trials (i.e. inattentional blindness); and correct rejections corresponding to ‘no’ responses on absent trials. Right: Formula for calculating criterion or response bias from hit rate (H), i.e. proportion of present trials in which subjects responded ‘yes’, and false alarm rate (FA), i.e. proportion of absent trials in which subjects responded ‘no’. c Criteria for Experiments 2, 4 and 5, showing that in each case subjects exhibited a significantly conservative bias, i.e. a tendency to say ‘no’ when asked if they noticed anything unusual, independent of the actual presence of a stimulus. This suggests that subjects in inattentional blindness experiments may systematically underreport their awareness of unexpected stimuli across different paradigms.