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R. W. Li, D. M. Levi; "Slow" Perceptual Learning of Vernier Acuity in Adult Amblyopia: An Intensive Amblyopia Treatment Study. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4889.
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Our previous studies1, 2 demonstrate that practicing position discrimination for roughly 20 hours improves acuity by about 20-30% in patients with amblyopia. In this study, we investigated the limits, time course and mechanisms of perceptual learning over extended periods of time (80-100 hours).
Adults with amblyopia (20-40-year-old) practiced a Vernier acuity task repeatedly until stable plateau performance was reached and maintained for 10-20 sessions. Vernier stimuli consisted of two abutting horizontal segments; each with 5 Gabor patches (carrier spatial frequency: 5, 6.6 or 10 cpd). Positional noise was added to the right segment by jittering the Gabor patches in vertical direction. We used an efficient 10-pass paradigm combined with reverse correlation3 to determine changes in "perceptive fields" and internal noise for positional judgments across sessions. Each session was approximately 1½ hours.
The amount of practice needed to reach plateau depends on the degree of amblyopia. Deep amblyopes (20/50-20/125) required more than 40 sessions (40-kilo trials) to reach plateau, and the threshold improvement was as much as 50-80%. In contrast, mild amblyopes (20/25-20/40) required fewer practice trials (~10 sessions) to obtain stable improvement (20-50%). We observed a dramatic optimization of perceptive fields and a substantial reduction in internal spatial distortion following practice.
Here we show that the mature amblyopic brain is surprisingly plastic and malleable. Using reverse correlation, we are able to document dramatic long-lasting perceptive field retuning in amblyopic vision. We believe this slow learning is unprecedented in normal vision. These findings suggest more intensive treatment is indicated for adult amblyopia.References:1. Li RW, Levi DM. J Vis 2004;6:476-87.2. Li RW, Young KG, Hoenig P, Levi DM. IOVS 2005;46:3161-8.3. Li RW, Levi DM, Klein SA. J Vis 2006;6:311-321.
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