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Srimant P. Tripathy, Dennis M. Levi; The ‘effective’ number of trajectories tracked in amblyopic vision. Journal of Vision 2006;6(6):768. doi: 10.1167/6.6.768.
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The ‘effective’ number of trajectories that can be tracked when detecting deviations in multiple trajectories depends on the angle of deviation, varying between one for a ±19° deviation and four for a ±76° deviation (Tripathy, Narasimhan & Barrett, 2005, Perception(Suppl.) 34 p. 12; also see Tripathy & Barrett, 2004, Journal of Vision 4 1020–1043). Is this ‘effective’ number of tracked trajectories compromised in amblyopic vision? The stimuli were linear, non-parallel, left-to-right trajectories moving at 4°/s. The number of trajectories (T) was varied (1–10). One trajectory deviated clockwise/anti-clockwise at the screen's mid-line. Deviations were blocked at ±76°, ±38° or ±19°. The proportions of correct identifications of deviation direction were determined for each T for the amblyopic and non-amblyopic eyes of strabismic and anisometropic amblyopes. The ‘effective’ number of tracked trajectories (A) was estimated from the hypothetical machine that matched the human observer's performance by perfectly tracking A of the trajectories and ignoring the remaining trajectories. In another experiment T was fixed (10, 8 or 6), and the number of deviating trajectories (D) was varied between 1 and T. For each combination of D and T the value of A was estimated. The effective numbers of trajectories tracked by the non-amblyopic eyes of amblyopes were comparable to numbers previously reported for normally-sighted observers (Tripathy et al., 2005, op. cit.) and were either the same as, or marginally higher than, the numbers for the fellow amblyopic eye. Resolution is not a primary factor limiting tracking performance when detecting large deviations in multiple trajectories.
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