Psychophysical investigations of the temporal modulation sensitivity function in amblyopia: spatiotemporal interactions.

Temporal modulation sensitivity functions were measured in response to counterphase sine-wave gratings of various spatial frequencies in seven strabismic and/or anisometropic amblyopes and in two stimulus-deprivation amblyopes. Both movement/flicker and pattern detection thresholds were determined. Strabismic and/or anisometropic amblyopes showed reduced sensitivity for movement/flicker and pattern detection in the amblyopic eyes, which were dependent on both the spatial and temporal frequencies of the stimulus and the detection criterion. At medium and high spatial frequencies, substantial reductions in movement/flicker detection were present, which were generally more marked for low temporal modulation frequencies. Reductions in pattern sensitivity were greater at the higher spatial frequencies, although some amblyopes showed losses in sensitivity at low spatial frequencies as well. The losses observed in the spatiotemporal transfer function of the amblyopic eyes were greater than those found with unstructured stimuli (uniform field flicker) and were not eliminated under reduced luminance. In subjects with amblyopia caused by stimulus deprivation, losses in spatiotemporal contrast sensitivity were either invariant across temporal frequencies or increased at higher rates of temporal modulations.