UBC Theses and Dissertations
Resolving inconsistencies in the maturation of human global motion perception Meier, Kimberly Megan
The typical development of motion perception is commonly assessed with tests of global motion integration using random dot kinematograms (RDKs). There are discrepancies, however, with respect to when typically-developing children reach adult-like performance on this task, ranging from as early as 3 years to as late as 12 years. While much research characterizes performance in terms of dot speed, there is evidence that different spatial and temporal components can impact performance on this task in adults and in children. Other studies suggest that the distance that dots are displaced each animation frame (∆x), rather than frame duration (∆t) or dot speed (∆x/∆t) per se, determines performance in developing macaques. No studies have directly investigated whether psychophysical performance follows this pattern in children. The current studies measured motion coherence thresholds in adults and children in two experiments. Experiment 1 examined differences in adult performance in two studies with similar RDK parameters except for the ∆x and ∆t used to make up similar speeds. This experiment tested four ∆x/∆t pairs yielding a speed of 1 deg/s, and held the number of presented frames constant, or the duration of the stimulus constant. These factors had no effect on the thresholds of adults. Experiment 2 was designed to replicate the results of macaque studies in human children, and compare their thresholds to adults. Two ∆t values were used in combination with seven ∆x values, for a range of speeds (0.3-38 deg/s). Adult thresholds followed a u-shape as a function of ∆x, with lower coherence thresholds for larger ∆t when ∆x was small. Child thresholds followed a rough u-shape as a function of ∆x, regardless of ∆t. Developmental comparisons showed children performed as well as adults for larger ∆x, and were immature for smaller ∆x. When parameters were expressed as speed, there was a range of intermediate speeds (4-12 deg/s) for which maturity was dependent on the values of ∆x and ∆t tested. These results resolve previous discrepancies by showing that motion sensitivity to a given speed may be mature, or not, depending on the underlying spatial and temporal properties of the motion stimulus.
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