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Endel Poder; Effect of phase on the detection of spatial patterns. Journal of Vision 2005;5(8):178. doi: 10.1167/5.8.178.
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© ARVO (1962-2015); The Authors (2016-present)
Ideal detectability of visual patterns should be determined by the contrast energy of the pattern. In general, experimental data are consistent with this idea. However, several authors have argued that there are special mechanisms sensitive to ecologically important spatial patterns, e.g. edges and lines.
In this study, I measured detection thresholds for phase-congruent (edges, lines) and phase-incongruent patterns with the same spatial frequency content and spatial extent.
The patterns consisted of 32 equal-amplitude spatial-frequency components.
Phase-incongruent patterns were generated from patterns with random phases by adjusting them for a minimal phase congruency. Four phase-incongruent patterns were compared with four phase-congruent ones.
The contrast thresholds were measured with 1-up 3-down staircase and 2-interval forced choice method. Presentation duration was 250 ms and stimulus extent (sigma of Gaussian window) was 1.5 deg. Location (absolute phase) was randomized.
The results for two observers show an elevation of thresholds for phase-incongruent patterns as compared with phase-congruent ones by factor 1.2 to 1.5. The results may indicate a presence of special edge-line detecting mechanisms. However, a simple non-linearity of contrast response function can probably also explain these results
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