Effect of exposure duration on spatial uncertainty in normal and amblyopic eyes

Previous studies have found that the spatial uncertainty of amblyopes is critically dependent on temporal factors. These studies claim that the spatial uncertainty is much greater at short exposure durations. We have reassessed the effect of exposure duration on the spatial uncertainty of normal and amblyopic eyes using a task in which we can compensate for the loss in contrast sensitivity which inevitably occurs as exposure duration is shortened. Our task involved a three-element alignment task, where each of the elements were spatial Gabors at two different separations. We ensured that our stimuli were always displayed at a fixed ratio above contrast detection thresholds at each exposure duration. Our results show that for normal subjects, for well separated equivisible stimuli, there is only a weak effect of exposure duration. A similar dependence is found for the dominant and amblyopic eyes of a group of strabismic amblyopes. Dominant eyes of strabismic amblyopes show increased spatial uncertainty compared with normal subjects. Amblyopic eyes of strabismic amblyopes show increased spatial uncertainty compared with their dominant fellow eye which is invariant with exposure duration. Some subjects show a larger positional deficit at short durations when the stimuli are almost abutting.