The role of perceptual similarity in visual search for multiple targets
The visual search for multiple targets can cause errors called subsequent search misses (SSM) – a decrease in accuracy at detecting a second target after a first target has been found (e.g. Adamo, Cain, & Mitroff, 2013). One of the possible explanations is perceptual set. After the first target is found, the subject becomes biased to find perceptually similar targets, therefore he is more likely to find perceptually similar targets and less likely to find the targets that are perceptually dissimilar. The experiment investigated the role of perceptual similarity in SSM errors. The search array in each trial consisted of 20 stimuli (ellipses and crosses, black and white, small and big, oriented horizontally and vertically), which could contain one, two or no targets. In case of two targets, they could have two, three or four shared features (in the last case they were identical). The features of target stimuli were indicated at the beginning of each trial. Participant's task was to find all the target stimuli or report their absence. Accuracy for conditions with two stimuli with two, three, four shared features and with one stimulus was compared. In case of two targets the correct answer assumed finding both stimuli. Repeated measures ANOVA revealed the main effect of shared features factor, F(1, 19) = 15.71, p = .000. Pairwise comparisons (with Holm-Bonferroni adjustment) revealed significant differences between all the conditions, except the conditions with one stimulus and two identical stimuli. SSM errors were found for all conditions, except fully identical stimuli condition. The size of SSM effect decreased with increasing the similarity between the targets. The results indicate the role of perceptual similarity and have implications for the perceptual set theory.