Abstract
Purpose::
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).
Methods::
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.
Results::
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.
Conclusions::
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.
Keywords: amblyopia • plasticity • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials