Volume 6, Number 6, Abstract 380, Page 380a doi:10.1167/6.6.380 http://journalofvision.org/6/6/380/ ISSN 1534-7362
Orientation discrimination in noise: 7-year-olds are noisier than adults
Terri L. Lewis
McMaster University, Hamilton Canada
[e-mail]
Dorita H. F. Chang
McMaster University, Hamilton Canada
Kathryn M. Murphy
McMaster University, Hamilton Canada
Daphne Maurer
McMaster University, Hamilton Canada
David G. Jones
McMaster University, Hamilton Canada
Abstract

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.
Support: CIHR grants MOP-36430 & MOP-13624 NSERC grant 175437-05.

History
Received March 23, 2006; published June 1, 2006
Citation
Lewis, T., Chang, D. H. F., Murphy, K. M., Maurer, D., & Jones, D. G. (2006). Orientation discrimination in noise: 7-year-olds are noisier than adults [Abstract]. Journal of Vision, 6(6):380, 380a, http://journalofvision.org/6/6/380/, doi:10.1167/6.6.380.
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