DEVELOPMENT OF DIRECTIONAL MOTION SYMMETRY IN THE MONOCULAR VISUALLY EVOKED-POTENTIAL OF INFANT MONKEYS

Motion processing in humans and monkeys exhibit a directional asymmetr y during infancy which is not present in adults except following abnor mal visual rearing conditions. To characterize the time course for mat uration of a symmetric response, we measured the monocular visually ev oked potential (MVEP) response to 0.26 c/deg gratings oscillating hori zontally at 6 Hz in 13 infant rhesus monkeys between 1 and 52 weeks of age. An asymmetric (F1) and a symmetric (F2) frequency component were extracted from the MVEP using Fourier analysis. At early ages the asy mmetric Fl component measured from the two eyes exhibited a 180 deg in terocular phase shift, demonstrating that there was a directional bias in opposite directions between the left and right eyes. Although our methods could not determine whether the bias was in the nasal or tempo ral direction, our results would be consistent with a nasal bias, as h as been observed in previous motion studies. Magnitude of the asymmetr y was quantified in the form of an asymmetry index, F1/(F1 + F2), Base d on developmental changes in the asymmetry index, and phases and ampl itudes of F1 and F2, we conclude that the MVEP loses its directional a symmetry at 6 weeks of age. The development of directional motion symm etry observed in monkeys over the first 6 weeks is similar to that obs erved in humans over the first 5 months. (C) 1998 Elsevier Science Ltd , All rights reserved.