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Terri L. Lewis, Dorita H. F. Chang, Kathryn M. Murphy, Daphne Maurer, David G. Jones; Orientation discrimination in noise: 7-year-olds are noisier than adults. Journal of Vision 2006;6(6):380. doi: https://doi.org/10.1167/6.6.380.
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We used a new high contrast stimulus containing a variable amount of orientation signal in unoriented noise (Jones et al., 2003) to test orientation discrimination in visually normal 7-year-olds and adults (n = 16/grp). The task on each trial was to indicate whether the signal was oriented horizontally or vertically. Percent signal was varied according to a QUEST staircase procedure and thresholds were taken as the lowest orientation signal for which performance was 82% correct. Across 4 runs, stimulus size decreased systematically from 6 − 0.75 deg. In a 5th run, we retested the 6 deg stimulus to rule out fatigue effects. Thresholds were higher in children than in adults and varied with stimulus size (ANOVA, p < .0002 for both). Specifically, at both ages, thresholds improved as size increased from 0.75 – 3 deg (p < .005 for all) and then reached an asymptote, showing no further improvement beyond 3 deg (p > .70). At asymptote, children required 18% signal to discriminate orientation accurately whereas adults required only 12%, indicating that intrinsic noise may be 1.5 times higher in 7-year-olds than in adults. Because contrast sensitivity and motion coherence thresholds are mature by 7 years of age (Ellemberg et al., 1999, 2002), the ability to extract a stationary oriented signal from noise likely involves different neural mechanisms that mature more slowly.
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