Perceptual learning for recovery of sight
Prof Uri Polat
Since the pioneering studies by Hubel and Wiesel, and their suggestion for a critical period for visual development, Amblyopia (the lazy eye syndrome) is typically treated at very early age by patching the strong eye, to allow the formation of stronger connections for the input arriving from the weaker eye. It was generally accepted that Amblyopia is untreatable in adulthood.
Our team member, Dr. Uri Polat and colleagues were the first to demonstrate that vision can be markedly improved in adults suffering from amblyopia using a novel perceptual learning technique (Polat et al., Proc Natl Acad Sci U S A. 101:6692-7, 2004). This is done by presenting an oriented Gabor stimulus at low contrast (target) together with co-aligned flanking stimuli of the same orientation and spatial frequency at different spatial distances (see below). The participant's task is to report the target stimulus orientation, and the target contrast is adjusted to maximize training in near-threshold conditions. Following training for 4-6 months, participants showed a major improvement in their visual acuity (78% compared to baseline, see learning dynamics in the Figure below). The contrast sensitivity was also remarkably improved. The treatment produced a significant improvement in sensitivity in all spatial frequencies, such that the CSF of amblyopic patients was within the normal range (shaded region). Similar improvement in visual acuity and contrast sensitivity was also found when applying the training on amblyopic children age 6-9 years old. These results suggest that corrective training using the simple paradigm described above, may well improve visual capabilities in our patient population.
Figure Legend: Left: The stimuli used in the training sessions. The spatial frequency, target contrast, and distance between target and flankers was manipulated to obtain the best learning results. Middle: Dynamics of CSF improvement. Grey zone indicates the normal range. The gains are sustained a year later. Right: Learning curves of adult amblyopic patients showing improved visual acuity. Black line shows patient without treatment.