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Anna Franklin, Di Catherwood, Emma Axelsson, James Alvarez; Lateralization of visual categories in infancy. Journal of Vision 2010;10(7):476. doi: https://doi.org/10.1167/10.7.476.
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How the two hemispheres of the adult brain contribute to categorical processing has been extensively investigated (e.g., Jager & Postma, 2003). However, despite categorization being a pervasive aspect of infant cognition, there is little understanding of how visual categories in infancy are lateralized. Here, we investigate the lateralization of categorical perception of orientation at 5-months. Although orientation is a continuum ranging from 0 to 360°, both adults and infants perceive it categorically. For example, infants dishabituate to a novel orientation when the novel and habituated orientations are from different categories (vertical and oblique) but not when from the same category, even when the degree of difference between novel and habituated stimuli is equated (e.g., Bomba, 1984). To investigate the lateralization of this category effect, a visual search task was used where oriented lines were presented in a ring around a central fixation point. One line (the target), which was presented to left or right visual fields (L/RVF), was a different orientation to the others (the distractors). Targets and distractors were either from the same category (15 and 30°) or from different categories (0 and 15°). Eye-movements were recorded, stimuli were presented only when centrally fixated, and latencies for a direct eye-movement to the target were analyzed. Infants were centrally fixated for the duration of the latency measure, ensuring that targets remained lateralized (Franklin, Drivonikou, Bevis, Regier, Kay & Davies, 2008). Infants were faster at initiating a direct eye-movement to the target amongst different- than same-category distractors, but only for targets in the RVF. As the RVF initially projects to the LH, orientation categories therefore appear to be LH lateralized at 5-months. The findings are contrasted to the lateralization of categorical perception of hue in infancy (Franklin et al., 2008) and are also related to the lateralization of visual categories in adults.
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