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Lisa Betts, Daphne Maurer, Terri Lewis; The development of sensitivity to the direction of motion. Journal of Vision 2011;11(11):419. doi: 10.1167/11.11.419.
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© ARVO (1962-2015); The Authors (2016-present)
Other than one study of infants (Banton et al., 2001), nothing is known about the development of sensitivity to motion direction. Here we investigated sensitivity to small deviations in the direction of motion in 5-year-olds, 7-year-olds, and adults (18–22 years; n = 20/group). Stimuli consisted of black dots (diameter = 2.5 or 10 min) moving coherently at 4.16 or 8.65 deg/s against a grey background. The task on each 1s trial was to indicate whether the dots moved to the left or right of a white vertical reference line. We used a 3-down, 1-up staircase to measure the minimum direction deviation that could be discriminated from vertical. Thresholds were based on the mean of two runs for each of the four dot size/speed conditions. There was a significant 3-way interaction between age, speed, and dot size (p < 0.01). Subsequent ANOVAs at each age revealed lower thresholds for the faster than the slower speed in both 7-year-olds (slower, M = 4.7°; faster, M = 2.5°) and adults (slower, M = 6.6°; faster, M = 1.8°) (ps < 0.01). This comparison was marginally significant in 5-year-olds (slower, M = 10.1°; faster, M = 6.9°; p = 0.054). Thresholds were comparable for the two dot sizes at 5 years (smaller, M = 8.4°; larger, M = 8.6°) and 7 years (smaller, M = 3.5°; larger, M = 3.6°). Surprisingly, in adults, thresholds were worse for larger than for smaller dots at the slower speed (small = 3.2°; large = 10.3°, p < 0.01) but not the faster speed (small = 1.6°; large = 2.0°). Poor performance for large, slowly moving stimuli in adults, but not 7-year-olds, may reflect the onset of inhibitory mechanisms after 7 years of age (e.g., Tadin et al., 2003).
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