When participants are attending to a subset of visual targets or events and ignoring irrelevant distractors (“selective looking”), they often fail to detect the appearance of an unexpected visual object or event even when the object is visible for several seconds (“sustained inattentional blindness”). An important factor influencing detection rates in selective looking is the attentional set of the participant: the more similar the features of the unexpected object are to the attended ones, the more probably it will be detected. We examined the possible contribution of active ignoring to this similarity effect by studying the role of the distractor objects in sustained inattentional blindness. First we showed the similarity effect for chromatic colors and then we manipulated the similarity of the unexpected object in relation to the distractor objects and did not find any effects. Moreover, we found that inattentional blindness was present even when the displays did not contain any irrelevant to-be-ignored objects. We conclude that attending to target items on the basis of attentional set, but not active ignoring of nontargets items, is sufficient for the occurrence of sustained inattentional blindness.
