Perceptual learning is gaining recognition as a potentially beneficial treatment for adults with amblyopia. However, it is unclear how consistent the training benefit is across subjects and tasks. We investigated this question in amblyopic non-human primates (Macaca nemestrina). We used an integrative training stimulus: random dot motion direction discrimination over a range of directions and dot speeds. We then tested for improvement in performance on various motion and form tasks post-training: coherent motion detection, Glass pattern form discrimination, contrast sensitivity, and Vernier acuity. As a control, we assessed the untrained fellow eye for any changes in performance. All data were collected using two-alternative forced-choice psychophysical methods. Four amblyopic monkeys, two strabismic and two anisometropic, and one visually-normal control were tested. The number of training trials for perceptual learning ranged from 15,000 a?? 30,000. Our results showed that 1) at least 20,000 training trials were needed for substantive perceptual learning to occur; 2) in most cases, learning transferred within the training domain to a non-practiced motion task, but there was less transfer across domains, to the spatial tasks; 3) contrast sensitivity improved in one-half of the cases but was poorer after training in the other cases; 4) form discrimination performance was typically poorer after training, with only 1 of the 4 amblyopes showing a clear training benefit; 5) Vernier acuity was mostly unaffected by the training; 6) in several cases, serendipitous improvement in the untrained fellow eye negated any benefit to the amblyopic eye. These results suggest that further evaluation is needed before perceptual learning can be considered a consistent, broadly effective and beneficial treatment for amblyopia.
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