Abstract
During motion induced blindness (MIB), visually salient objects vanish from awareness when presented on a background of coherent motion. Here we investigate the influence of item-number, group-number and attentional demand on the perceptual disappearance of individual stimulus targets. In Experiment One, 1–4 square targets (varying in color and angular rotation) were each presented centered within one of the four visual quadrants. Disappearance of a single target presented alone averaged 23.4% of the 40 second trials. Surprisingly, the total proportion of disappearance increased only moderately to 28.7% when the maximum number of 4 targets was presented, while the disappearance of any individual target, reduced by more than half to an average of 11.4% of the trial. In Experiment Two, the effect of group number was considered. In every trial, all 4 target squares were presented within the same quadrant. Targets defined as “in-group” shared feature properties (color, texture, proximity and alignment of border contours), “out-group” targets differed in respect to all features. Despite only moderate effects of the grouping cues (i.e., simultaneous disappearance of all 4 targets only increased from 0.5% when targets formed 4 out-groups to 2% when targets formed a single group), an increase in group number lead to greater total disappearance without any associated increase in the disappearance of the individual targets. In Experiment Three, we selectively manipulated attentional load with a central detection task. Subjects reported less disappearance of a single target in high attention conditions relative to fixation and low attention conditions. In all experiments, a simulated MIB condition ruled out the effect of task difficulty or response inaccuracy. Together these results indicate a striking paradox: the more attention allocated towards a target object, the more it will be suppressed from awareness. A number of mechanisms are considered to explain this surprising effect.