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Helle K. Falkenberg, Peter J. Bex; Perception of expanding optic flow patterns across the visual field. Journal of Vision 2004;4(8):605. doi: https://doi.org/10.1167/4.8.605.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the sensitivity to the direction of heading in expanding optic flow fields as a function of retinal location, with a view to determine the likely functional deficit in low vision patients with visual field loss. The results reported here are from a preliminary study investigating three normal vision observers. Methods: Sensitivity to the focus of expansion (FoE) was measured with 0.5 second expanding random Gaussian dot patterns as a function of retinal location. Accuracy was measured by positioning a cursor on the perceived FoE. Observers also discriminated whether the FoE was left or right of centre in an equivalent noise paradigm in which positional variance was applied to the FoE for each dot. Finally to determine FoE resolution, observers discriminated an interval containing two FoEs from an interval containing only one. Results: The accuracy of locating the FoE was independent of eccentricity and location of the expanding optic flow in the visual field. This was confirmed by the equivalent noise measurements which showed that internal noise did not vary with eccentricity but efficiency decreased somewhat. The separation between two FoEs had to increase with eccentricity before an observer could resolve them. Conclusions: Sensitivity to expanding optic flow patterns is generally invariant across the field for both identifying the position of the FoE and for integrating the motions of the dots defining it. The results suggest that mechanisms with large receptive fields pool directional information across the visual field. The loss in efficiency indicates that the number of elements integrated increases with eccentricity and this also accounts for the loss of resolution.
The Wellcome Trust
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