Is the ability to track multiple objects compromised by amblyopia?

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Abstract
Amblyopia results in a severe loss of positional information and in the ability to accurately enumerate objects (Sharma et al, 2000, Nat. Neurosci., 3, 496–501). In this study, we asked whether amblyopia also disrupts the ability to track a near-threshold change in trajectory of a single target amongst multiple targets. In the first experiment we examined the precision for detecting a deviation in the linear motion trajectory of a dot by measuring deviation thresholds as a function of the number of moving trajectories (T). As in normal observers, we found that in both eyes of amblyopes, threshold increases steeply as T increases from 1 to 4. Surprisingly, for T = 1 to 4, thresholds were essentially identical in both eyes of the amblyopes, and were similar to those of normal observers. To test whether the motion system is ‘spared’ in amblyopia, a second experiment measured the precision for detecting a deviation in the orientation of a static bilinear ?trajectory? by again measuring deviation thresholds (i.e., angle discrimination) as a function of the number of oriented line ?trajectories? (T). Relative to the non-amblyopic eye, amblyopes show a marked threshold elevation for a static target when T = 1. However, thresholds increased with T with the same slope as in the preferred eye, and that of the normal controls. We conclude that while amblyopia disrupts static angle discrimination, amblyopic dynamic deviation detection thresholds are normal; amblyopes are able to effectively monitor approximately one near-threshold trajectory (Tripathy & Barrett, 2004, J Vis., 4, 1020-1043).

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