Top-down guidance of visual search is an issue of continuous discussions (e.g. Wolfe, Horowitz, 2017). However, it’s still unclear when guidance emerges in the course of individual development, and whether the fronto-parietal brain network, which underpins attentional control, is necessary for the attentional guidance. Although there were a number of experiments studying visual search in children, to our knowledge no study directly confronted conditions, under which adults do and do not demonstrate guided search, in younger populations. In our experiment, we compared feature search, guided conjunction search and unguided conjunction search in 20 young adults (university students, mean age 18.5) and 20 junior schoolchildren (7.5–9.5 years old, mean age 8.5). The two groups performed three randomized blocks of the standard visual search task, searching for a target “fox’s house” among distractor houses and receiving feedback after each trial. The target house differed from distractors only in color (feature search), in color and shape (conjunction search), or was defined as a specific combination of two colors (conjunction search with no possibility of top-down guidance). Set sizes of 4, 7, and 10 stimuli were used, with only a half of the trials containing a target. Our hypothesis was that in adults we would observe top-down regulation of the conjunction search, whereas in children the search besides the feature search condition will be equally inefficient, because of the fron-to-parietal network immaturity (e.g. Astle et al., 2015). Surprisingly, the overall pattern of results in all three conditions was the same in children and adults, with pronouncedly more efficient conjunction search as compared to the unguided search, although children were significantly (and proportionally) slower in all types of search. This allows concluding that top-down attentional guidance is already fully present in junior schoolchildren.
The heterogeneity of our visual environment typically reduces the speed with which a singleton target can be found. Visual search theories explain this via nontarget similarities and dissimilarities that affect grouping, perceptual noise, etc. Here, we show that increasing the heterogeneity of a display can facilitate rather than inhibit visual search for size and orientation singletons when heterogeneous features smoothly fill the transition between highly distinguishable nontargets. We suggest that this smooth transition reduce the “segmentability” of dissimilar items to otherwise separate subsets making the visual system to treat them as a near-homogenous sets opposing to a singleton.