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Terri Lewis, Allison Sekuler, Patrick Bennett; Psychophysical measurements of surround suppression in 5-year-olds. Journal of Vision 2008;8(6):388. doi: 10.1167/8.6.388.
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At low contrasts, increasing stimulus size can improve performance, a phenomenon known as spatial summation. At high contrasts, young adults show spatial suppression: worse direction discrimination as stimulus size increases (Anderson & Burr, 1991; Betts et al., 2005; Tadin et al., 2003). Such spatial suppression has been attributed to GABA mediated inhibitory connections among cortical cells (Jones et al., 2001). Recent results suggest that children may have decreased GABAergic inhibition (Boley et al., 2005); if so, they should show decreased spatial suppression. Methods. To assess changes in spatial suppression with age, we measured motion discrimination thresholds as a function of pattern contrast and size in 27 5-year-olds and 24 young adults. In 4 separate blocks, participants viewed small (2σ = 0.7°) or big (2σ = 5°) 1 cpd Gabor patterns of high (92%) or low (4%) contrast, moving at 8°/sec. Participants judged the direction of motion as leftward or rightward. Stimulus duration varied over trials to determine the minimum duration needed for accurate performance. Results. At low contrast, duration thresholds were 1.9 times longer for children than adults (p 0.30). At high contrast, thresholds were worse for big than small patterns (p [[lt]]0.00001) and worse for children than adults (p = 0.03). The amount of spatial suppression was smaller in children than adults (p = 0.03, 1-tailed) because children were worse than adults for small but not big patterns. Conclusion. In general, 5-year-olds require more time than young adults to process the direction of motion. Critically, at high contrasts, the suppression index is smaller in 5-year-olds than adults, consistent with the hypothesis that 5-year-olds, like the elderly (Betts et al., 2005), have weaker inhibitory surrounds than young adults.
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