The robustness of infants' detection of visual motion

Fourteen-week-olds were tested for detection of the movement of a small vertical bar with varying levels of visual complexity using a speeded version of the forced-choice preferential looking (FPL) paradigm. The target bar horizontally oscillating at temporal frequencies of 0.6, 1.2 or 2.4 Hz could appear amidst 1, 5, or 13 other static bars. Detection accuracy was (a) generally unaffected by the complexity of the visual field, (b) affected by the distance of the moving bar from the center of the screen, and (c) affected directly by temporal frequency. Response times depended inversely on temporal frequency. When the similarity of the static elements was decreased by making them chromatically heterogeneous, the FPL observer's average response time increased, although detection accuracy remained the same. The FPL observer's response times actually decreased slightly as more heterogeneous distracters were added. Adults tested using an FPL observer also showed this same effect. Both infants and adults showed disproportionately long response times on incorrect trials when only 1 other distracter was present in the visual field. The number of static elements in the visual field and their similarity affected primarily the speed with which infants at this age responded to movement.