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Vickie L. Armstrong, Terri L. Lewis, Daphne Maurer; Moving into adult vision: five-year-olds' immaturities in detecting second-order motion versus discriminating its direction. Journal of Vision 2005;5(8):662. doi: 10.1167/5.8.662.
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We compared sensitivity to second-order (contrast-modulated) motion in 5-year-olds and adults using tasks that required the detection of motion vs. the discrimination of the direction of motion. For the motion detection task, participants viewed two 15x15° vertical sine-wave gratings separated by a 5° gap. Randomly, on each trial, one grating was stationary and the stripes in the other moved outward. Participants indicated which grating was moving. For the direction discrimination task, participants viewed one 15x15° vertical sine-wave grating that moved randomly to the left or right on each trial, and indicated the direction of motion. Each participant was tested on one of four temporal frequency-velocity combinations for each task. Contrast was modulated over trials according to a staircase procedure (Harvey, 1986) to measure the minimum contrast modulation yielding 82% correct responses. Results to date from 16 adults and 16 5-year-olds indicate that 5-year-olds' thresholds are lower for detecting motion than for discriminating its direction (p p > .20). Mean thresholds were lower in adults than in 5-year-olds for both tasks (p s < .001). The findings suggest that, at 5-years of age, the neural mechanisms underlying the detection of second-order motion are more mature than the mechanisms underlying the discrimination of the direction of second-order motion. A possible explanation is that, under the conditions tested, 5-year-olds relied on relatively mature temporal frequency-sensitive mechanisms to detect motion and relatively immature motion-sensitive mechanisms to discriminate the direction of motion. This hypothesis is supported by evidence that sensitivity to high temporal frequencies is mature at 12 weeks of age (Regan, 1981), while sensitivity to direction of second-order motion is still immature at 5 years of age (Ellemberg et al., 2003).
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