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Aaron Johnson, Rick Gurnsey; Perception of shape-from-texture in the periphery using a simulated central scotoma. Journal of Vision 2009;9(8):36. doi: 10.1167/9.8.36.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Studies of eccentricity dependent sensitivity loss typically require participants to maintain fixation while making judgments about stimuli presented at various eccentricities in the peripheral visual field. However, training participants to fixate can prove difficult. Therefore, we have developed a novel alternative in which eccentricity of stimulus presentation is controlled using a simulated central scotoma of variable size.
Method. Participants were asked to identify 3D surfaces comprising hills, valleys and plains in three possible locations. Therefore there were 27 different surfaces, yielding a 27 alternative forced choice task. Surface shape was conveyed by texture. Participants performed the task for simulated scotomas of 0, 1, 2, 4, 8 and 16° diameter over an eight-fold range of stimulus sizes. Position of scotoma was based on current fixation location captured with an eye tracker (SR Research Eyelink 1000, binocular tracking).
Results. The psychometric functions for each simulated scotoma were left shifted versions of each other on a log size axis. Therefore, when we divided stimulus size at each eccentricity (E) by an appropriate F = 1 + E/E2 (where E2 is the eccentricity at which stimulus size must double to achieve equivalent-to-foveal performance) all thresholds collapsed onto a single psychometric function. Therefore, stimulus magnification was sufficient to equate sensitivity to shape-from-texture for all scotoma sizes. The average E2 value required to achieve this was 1.67° (N = 4, SEM = 0.304, 95% CI - 0.62° to 2.73°).
Conclusions. In all cases, scaling with F = 1 + E/E2 eliminated most scotoma-dependent variation from the data. The data show clear evidence that size scaling is sufficient to equate the perception of shape-from-texture across in the presence of scotomas.
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