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James D. Hilger, Philip J. Kellman; Tolerance for misalignment in contour interpolation: retinal or relational?. Journal of Vision 2005;5(8):571. doi: 10.1167/5.8.571.
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© ARVO (1962-2015); The Authors (2016-present)
Problem: Contour interpolation has been shown to be scale-invariant in some respects, as in the effect of support ratio on contour strength. Kellman & Shipley (1991) hypothesized that the mathematical criteria of contour relatability included a small tolerance for misaligned parallel edges. Empirical estimates have suggested that collinear edges can be misaligned up to about 15 arc min and still support interpolation. We investigated whether a retinal metric or a scale-invariant notion, such as ratio of misalignment to edge separation, could account for the data. Methods: Tolerance for misalignment was tested in a two interval, forced choice, path detection paradigm. Targets were paths of 4 spatially separated contour segments (illusory contour inducers) that were collinear or misaligned to varying degrees. Paths were presented in noise consisting of identical contour segments, randomly oriented. The target inducers were collinear or misaligned relative to the axis of global alignment. Within each level of retinal misalignment, inducers were positioned to create 5 different relative angles between interpolating elements. Results: Angular misalignment had no independent effect on performance. Instead, a retinal tolerance of 10–15 min was confirmed. There was a reliable interaction between relative and retinal misalignment; at retinal misalignments beyond 10–15 arc min, larger relative angles markedly lowered performance. The geometry of the displays dictated that this increase in relative angle increased the distance (gap size) between the target elements. Further experiments tested whether this interaction was limited to interpolation or involved other grouping processes. Conclusions: Tolerance for misalignment is largely determined by a retinal metric. Angular misalignment appears to modulate residual interpolation effects beyond 10–15 arc min, a result that may be explainable in terms of increased position or orientation uncertainty for more separated contours.
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