Abstract
Abstract: :
Purpose: We were interested in studying integration mechanisms of second–order orientation across space, in amblyopia. The deficiency in detecting and discriminating of these stimuli reported before (Wong et al. 2001) motivated us to investigate whether amblyopes are abnormal in higher level visual functions such as integration too. Methods: 8 amblyopic and 8 normal subjects were recruited for this experiment. The visual acuity of the amblyopic subjects varied between 20/40–20/200. Sixteen arrays of second–order modulated Gabor micro–patterns were presented to the subjects. Subjects judged whether the overall orientation of the texture was tilted to right or left of vertical. Prior to this, we matched the visibility of a single Gabor for amblyopic (AE) and non–amblyopic NAE) eyes. Firstly, we measured the detection threshold for the carrier and then in order to measure the modulation depth threshold for envelope, we used a horizontal/vertical discrimination task using the same multiples of threshold contrast for the carrier for AEs and NAEs. Subsequently, presenting one oriented Gabor and using similar multiples of threshold modulation depth, we matched the orientation discrimination performance for NA and NAE. Paching one eye at a moment, observers performed all tasks monocularly. Results: Our severe amblyopes showed significant differences in detecting the carrier. Although most amblyopic subjects needed higher modulation depths than the normal subjects to discriminate the stimuli, the difference between the AE and NAE was very small. The performance of the amblyopic subjects using AEs and NAEs to estimate mean orientation was the same and similar to normal subjects. In all AE, NAE and normal eyes we found high internal noise and low sampling efficiency. Conclusions: Although the AE is deficient in terms of first– and second–order inputs, if the visibility of the carrier is equated, the integration of second order information is similar to normal. Interestingly, the NAEs of the amblyopic subjects have the same deficiency as their AEs.
Keywords: amblyopia • space and scene perception