Infant motion: detection (M:D) ratios for chromatically defined and luminance-defined moving stimuli.

In order to assess the relative contributions of chromatic vs luminance information to motion processing in infants, we employed a motion:detection (M:D) paradigm. Stimuli consisted of 27 deg by 40 deg, 0.25 c/deg sinusoidal gratings moving at 22 deg/sec (5.6 Hz), and were either chromatically defined or luminance-defined. Contrast thresholds for direction-of-motion (M) were obtained using a directional eye movement technique. Contrast thresholds for detection (D) were obtained using forced-choice preferential looking. M:D threshold ratios were obtained for individual infant subjects, and results were compared to those of adults. As expected, adult M:D threshold ratios were near 1:1 for luminance-defined stimuli, but greater than 1:1 for chromatically defined stimuli. This suggests that, for adults, luminance-defined, but not chromatically defined, stimuli are detected by mechanisms labeled for direction of motion. By contrast, infant M:D ratios for chromatically and luminance-defined stimuli were approximately equal and close to 1:1, suggesting that, for infants, luminance- as well as chromatically defined stimuli are detected by mechanisms that are labeled for direction of motion.