Psychophysical and electrophysiological investigations of amblyopia : uniform field and spatio-temporal interactions

Amblyopia is typically thought to be an anomaly of spatial vision. The studies reported here were conducted to determine if an anomaly is also present in the temporal processing abilities of the amblyopic eye and to what extent spatial processing is influenced by the temporal characteristics of the stimulus. Both psychophysical and electrophysiological experiments were conducted with amblyopic observers of varying etiology (strabismic and/or anisometropic amblyopia and stimulus deprivation amblyopia) using a uniform field and sine-wave gratings counterphase modulated at different temporal frequencies. The temporal modulation sensitivity functions measured psychophysically using a large uniform field showed a decrease in sensitivity of the amblyopic eye for low and middle temporal frequencies in about half of the strabismic and/or anisometropic amblyopes tested. In severe amblyopia secondary to stimulus deprivation, the losses in sensitivity were larger than those measured in strabismic and/or anisometropic amblyopes and were present at all temporal frequencies. When spatial structure was introduced and the temporal modulation sensitivity function was measured for sine-wave gratings of various spatial frequencies, the losses in sensitivity of the amblyopic eye were greater than those measured with the large uniform field. All amblyopic observers showed losses in movement/flicker detection which were greater at high spatial frequencies modulated at low temporal frequencies. While the losses in pattern sensitivity were also greater at high spatial frequencies, they were either uniform across all temporal frequencies or greater at the lower temporal modulation frequencies. [...]