Purchase this article with an account.
S Hariharan, H Tran, DM Levi, SA Klein; What Limits Counting in Strabismic Amblyopia? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4689.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Strabismic amblyopes underestimate the number of features presented to their amblyopic eye. This undercounting represents a limitation in their ability to distinguish and to individuate the features with their amblyopic eye. The purpose of this study was to ask whether the undercounting shown by amblyopes is due to a limit in attentional capacity (i.e. the number of items one can attend to) or a limit in attentional resolution (i.e. in the spacing of items). Methods: Five amblyopes and three normal observers participated in the study. Viewing was monocular. The stimuli were briefly presented, high contrast (100%) Gabor patches. In experiment 1, N patches (where N= 3, 5 or 7) were presented, randomly positioned on a 7X7 square array of possible positions. The observers recorded the number of patches presented in a given trial. In experiment 2, the stimulus was a 7X7 square array of Gabor patches, with N patches randomly removed from the array (where N = 3, 5 or 7). The observers recorded the number of «missing patches’. In experiment 3 observers had to estimate the number of vertical Gabor patches (N= 3, 5 or 7) among distractor horizontal Gabor patches in the same 7X7 array. A capacity limit predicts that undercounting will increase with N; a resolution limit predicts that undercounting will increase as separation decreases. Results: Amblyopic observers markedly undercounted the number of features (experiment 1) number of missing features (experiment 2) and number of different features (experiment 3) with their amblyopic eyes. Undercounting was maximum when N was greater than 3 and at greater viewing distances. Undercounting was either independent of separation, or decreased as patch separation decreased, opposite from the resolution prediction. Conclusion: Our data suggests that the undercounting seen in amblyopic observers can be attributed to a limit in capacity rather than to a limit in resolution. Since low-level explanations cannot completely explain the separation independence we suggest that our results reflect a higher-level limitation in the number of features the amblyopic observers can individuate.
This PDF is available to Subscribers Only