Abstract
During early development, distorted and blurred optical input from the eyes leads to neurophysiological changes in the visual system. Typically, optical blur in one meridian occurs in normal development, and young children often need optical astigmatic corrections. Maturation of neural connectivity is experience-dependent, and adaptation to uncorrected visual input during development may be inferred from visual functions in adults. A recent study suggested that spatial interactions in adults with oblique astigmatism are reminiscent of meridional amblyopia's abnormal development which are sub-normal on the blurriest meridian. Another study shows that adaptation to blur improves with experience, efficiently engaged when blur is reapplied and vice versa. We ask whether cortical blur adjustment during early development affects shape perception in astigmatic adults. Ten optically corrected participants, astigmatic and controls (non-astigmatic), were tested in several repeated sessions with a proximity-grouping task, employing a circular dots array (R=6 dots), varying horizontal (dh) and vertical (dv) dots-spacing. Participants reported the perceived orientation of the array (horizontal or vertical). Seven (dh/dv) configurations were tested in 40 and 80 ms stimuli duration, with dh/dv<1 introducing a horizontal bias. A robust perceptual bias (p=0.016) was found toward a direction orthogonal to the blurred meridian during childhood for fully corrected astigmatic (~3%±0.9; Mean±SE) but not control participants (~0%±0.08). The bias was found to increase with reaction time and with stimulus duration between ~2%±1.2 (fast) to ~4%±1 (slow). The bias found may represent a persisting adaptive correction, developed to compensate for the biased visual input during early life before the optical correction was applied, only partly eliminated after correction. In the context of the drift-diffusion model, we interpret the increased bias at longer reaction times (and duration) as an adaptive change in sensitivity during development, partially compensated by a probability-prior added after correction.