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S.T. L. Chung, R.W. Li, D.M. Levi; Performance for Identifying Contrast–Defined Letters in Adults With Amblyopia Benefits from Perceptual Learning . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5362.
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© ARVO (1962-2015); The Authors (2016-present)
Evidence exists suggesting that amblyopes show deficits in processing second–order spatial information. Because there is a significant degree of plasticity in the visual pathway that processes first–order spatial information in adults with amblyopia, in this study, we asked the question of whether or not the ability to process second–order stimuli also benefits from perceptual learning in adults with amblyopia.
Eight observers with amblyopia were trained to identify contrast–defined (second–order) letters using their amblyopic eyes. Before and after training, we determined observers' contrast thresholds for identifying luminance–defined (first–order) and contrast–defined letters, embedded within a field of white luminance noise, separately for the non–amblyopic and amblyopic eyes. Training consisted of 80 blocks (10 blocks per day) of identifying contrast–defined letters for the amblyopic eye. Letters were the 26 lowercase letters of the Times–Roman alphabet. Letter size was 1.3x the acuity–threshold for identifying salient contrast–defined letters in the amblyopic eye. Luminance–defined letters were defined by a luminance difference between the stimulus letter and its mid–gray background. Contrast–defined letters were defined by a differential noise contrast between the group of pixels that made up the stimulus letter and the group of pixels that made up the background.
Following training, 7 of the 8 observers showed a reduction (range: 10–73%) in contrast thresholds for identifying contrast–defined letters in the amblyopic eye. Three of these observers also showed a partial transfer of improvement to their fellow untrained non–amblyopic eye for identifying contrast–defined letters. None of the observers showed any improvement in identifying luminance–defined letters, for the non–amblyopic or the amblyopic eyes.
Similar to first–order spatial tasks, adults with amblyopia showed improvement in their performance for identifying contrast–defined letters (a second–order task) in their amblyopic eyes following training. This finding suggests a sizeable degree of plasticity in the visual pathway for processing second–order spatial information. Our result also implies that perceptual learning might be useful in reducing deficits in processing second–order spatial information in amblyopes.
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