Maturation of binocular luminance interaction in normal young and adult rhesus monkeys

Purpose: Our aim was to answer three questions 1) Do adult rhesus monkeys h ave binocular luminance interactions (BLIs) similar to those found in adult humans? 2) Is BLI in very young rhesus monkeys functionally mature? 3) If not, how does it change with age? Methods: We recorded visually evoked potentials (VEPs) in response to sinus oidally modulated uniform fields. The fields were presented dichoptically b y varying the relative temporal phase between the two eyes. Monkeys varied in age from 5.6 weeks to 5.25 years. Results: VEPs were Fourier analyzed and the relative second harmonic amplit udes were taken as the response measure. The second harmonic amplitudes in adult monkeys had an asymmetrical 'V-shaped' function as interocular phase difference (IPD) varied from 0 degrees to 180 degrees, as had been observed previously in adult humans [1]. The youngest monkeys exhibited a symmetric al pattern which became more asymmetrical at older ages and was adult like by about 19 weeks. Asymmetry magnitude and log age correlated 0.97 (p < 0.0 5) in the monkeys younger than 19 weeks. Conclusions: The adult rhesus data are consistent with a model derived from humans which involves two types binocular luminance processing. One combin es monocular responses nonlinearly (MNL) and a second combines monocular re sponses linearly followed by a binocular nonlinearity (MLBNL). These two pr ocesses have been associated with the parvocellular (P-) and magnocellular (M-) streams. Within this framework, the data from the youngest monkeys ind icate that BLI in the P-stream is relatively less mature at birth than that in the M-stream and develops reaching functional maturity on these measure s by around 19 weeks.