title: Target-distractor similarity has a larger impact on visual search in school-age children than spacing.
abstract: In typically developing children, crowding decreases with increasing age. The influence of target-distractor similarity with respect to orientation and element spacing on visual search performance was investigated in 29 school-age children with normal vision (4- to 6-year-olds [N = 16], 7- to 8-year-olds [N = 13]). Children were instructed to search for a target E among distractor Es (feature search: all flanking Es pointing right; conjunction search: flankers in three orientations). Orientation of the target was manipulated in four directions: right (target absent), left (inversed), up, and down (vertical). Spacing was varied in four steps: 0.04°, 0.5°, 1°, and 2°. During feature search, high target-distractor similarity had a stronger impact on performance than spacing: Orientation affected accuracy until spacing was 1°, and spacing only influenced accuracy for identifying inversed targets. Spatial analyses showed that orientation affected oculomotor strategy: Children made more fixations in the "inversed" target area (4.6) than the vertical target areas (1.8 and 1.9). Furthermore, age groups differed in fixation duration: 4- to 6-year-old children showed longer fixation durations than 7- to 8-year-olds at the two largest element spacings (p = 0.039 and p = 0.027). Conjunction search performance was unaffected by spacing. Four conclusions can be drawn from this study: (a) Target-distractor similarity governs visual search performance in school-age children, (b) children make more fixations in target areas when target-distractor similarity is high, (c) 4- to 6-year-olds show longer fixation durations than 7- to 8-year-olds at 1° and 2° element spacing, and (d) spacing affects feature but not conjunction search-a finding that might indicate top-down control ameliorates crowding in children.
authors.affiliation: Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Department of Cognitive Neuroscience, Nijmegen, The Netherlands Bartiméus, Institute for the Visually Impaired, Zeist, The Netherlands.
authors.forename: Bianca
authors.initials: B
authors.lastname: Huurneman
authors.affiliation: Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Department of Cognitive Neuroscience, Nijmegen, The Netherlands Bartiméus, Institute for the Visually Impaired, Zeist, The Netherlands.
authors.forename: F Nienke
authors.initials: FN
authors.lastname: Boonstra
mesh_terms: D002648:Child; D002675:Child, Preschool; D003441:Crowding; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010469:Perceptual Distortion; D014792:Visual Acuity / Q000502:physiology
keywords: children; crowding; eye movements; masking; visual search