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Terri L. Lewis, Andrea Kingdon, Dave Ellemberg, Daphne Maurer; Sensitivity to tilt in first-order and second-order gratings is immature in 5-year-olds. Journal of Vision 2005;5(8):187. doi: 10.1167/5.8.187.
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We measured orientation discrimination in 24 5-year-olds (± 3 months) and 24 adults (18 – 25 years of age) for first-order (luminance-modulated) and second-order (contrast-modulated) gratings. To achieve equal visibility, contrast for each age and condition was set at a fixed multiple of threshold contrast for discriminating horizontal from vertical gratings. For the test of sensitivity to orientation, the subject's task on each trial was to indicate whether the stripes were tilted to the left or right of vertical. Tilt was varied over trials according to a ML-TEST staircase procedure (Harvey, 1986) to measure the minimum tilt that could be discriminated from vertical 82% of the time. An ANOVA showed that tilt discrimination was immature in 5-year-olds (main effect of age, p p > 0.20). Specifically, the minimum discriminable tilt was 4 – 5 times worse in 5-year-olds than adults for both first-order patterns (adult mean = 0.9°; 5-year-old mean = 4.4°) and for second-order patterns (adult mean = 1.4°; 5-year-old mean = 5.5°). These immaturities are unlikely to be caused by motivational or attentional factors because 5-year-olds have nearly adult-like values for other thresholds measured with similar methods (Ellemberg et al., 2003). Thus, the neural mechanisms mediating orientation discrimination appear not to become adult-like until some time after 5 years of age. Moreover, thresholds at both ages were significantly worse (1.2 – 1.5 times worse) for second-order modulation than for first-order modulation (main effect of stimulus type, p < 0.01). This difference provides further support for the hypothesis (e.g., Chubb & Sperling, 1988) that the processing of first- and second-order information is mediated, at least in part, by separate mechanisms.
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