Shape temporal integration following late emergence from blindness
Description
Description We studied Ethiopian children that were effectively blind throughout childhood due to bilateral early-onset cataracts, and were surgically-treated only years later. We tested their anorthoscopic vision under slit-viewing conditions, because it requires demanding temporal integration processes, to perceive veridical shape. Failure to perform the task may allow mapping specific bottlenecks for late visual recovery. Shape temporal integration was assessed in two slit-viewing experiments using two groups of participants ('patients', 23 sight-retrieval patients, ages 8.2 - 19.9 years, mean = 12.3 years, and 'controls', 51 typically developing Ethiopian and Israeli children with normal or corrected vision, ages 7.8 – 15.0 years; mean = 11.4 years). Experiment I: In each trial, a shape moved behind a stationary slit. Next, the participants from both groups were presented with that shape and its flipped image (the foil), and were required to choose the shape they had just seen. The slit width was adaptively changed using a staircase procedure to assess the recognition threshold (in slit width). The shapes were a cross-like image and its flipped version. Both stimuli comprised of the same local elements. Many patients failed to use temporal integration for shape recovery in anorthoscopic conditions, although they could infer the direction of global motion (a prerequisite for recovery of veridical shape in these conditions). To test if this capability can be acquired with repeated practice on the task eleven patients were retested again later. Almost all of them could judge shape after further practice, at a level similar to controls. Experiment II: A litmus test for a true, newly-acquired shape recovery capability is that it is generalized, allowing recovery of any shape in similar slit-viewing conditions. We therefore conducted Experiment II utilizing 24 novel shape pairs. Each shape pair was generated such that the characteristic local visual features (i.e. contour curvature) were highly similar between the two shapes. Crucially, during the whole session, each image (chosen from the 48 unique shapes) was shown traversing across the slit only once. The results showed that that the acquired temporal-integration capability often transferred to novel stimuli, in the same slit-viewing conditions. Thus, learning was not limited to the specific visual features of the original shapes. These results indicate that plasticity of sophisticated visual inference routines is preserved well into adolescence and vision restoration after prolonged early-onset blindness is feasible to a greater extent than previously thought. Thus, despite early visual deprivation, complex visual inference routines can be acquired well into adolescence.