Infants code the direction of chromatic quadrature motion

The present experiment uses a quadrature motion paradigm to investigate the motion correspondence cues used by young infants for coding the direction of motion of red/green isoluminant gratings. Three-month-old infants and ad ults were tested with 0.25 c/d luminance-modulated or red/green isoluminant gratings, either moving continuously or shifted in spatial quadrature. Bot h direction-of-motion and detection thresholds were measured, and motion:de tection (M:D) threshold ratios were examined. Infants, like adults, could c ode the direction of motion of red/green quadrature-shifted gratings. In ad ults, M:D ratios were similar for continuous and quadrature motion. In infa nts, M:D ratios were higher for quadrature than for continuous motion, but elevations of similar magnitude were seen for both luminance-modulated and red/green gratings. The results suggest that frequency-doubled signals, suc h as those often seen in the magnocellular (M-cell) pathway, are not necess ary for coding the direction of motion of isoluminant gratings in infant su bjects. Two other theoretical options-mediation by the scatter of isolumina nce points in the M-cell population, and parvocellular (P-cell) mediation-a re discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.