Qualitative Cues in the Discrimination of Affine-Transformed Minimal Patterns

Abstract

Abstract. An important factor in judging whether two retinal images arise from the same object viewed from different positions may be the presence of certain properties or cues that are 'qualitative invariants' with respect to the natural transformations, particularly afine transformations, associated with changes in viewpoint. To test whether observers use certain afine qualitative cues such as concavity, convexity, collinearity, and parallelism of the image elements, a 'same-different' discrimination experiment was carried out with planar patterns that were defined by four points either connected by straight line segments (line patterns) or marked by dots (dot patterns). The first three points of each pattern were generated randomly; the fourth point fell on their diagonal bisector. According to the position of that point, the patterns were concave, triangular (three points being collinear), convex, or parallel sided. In a 'same' trial, an afine transformation was applied to one of two identical patterns; in a 'different' trial, the afine transformation was applied after the point lying on the diagonal bisector was perturbed a short, fixed distance along the bisector, inwards for one pattern and outwards for the other. Observers' ability to discriminate 'same' from 'different' pairs of patterns depended strongly on the position of the fourth, displaced, point: performance varied rapidly when the position of the displaced point was such that the patterns were nearly triangular or nearly parallel sided, consistent with observers using the hypothesised qualitative cues. The experimental data were fitted with a simple probabilistic model of discrimination performance that used a combination of these qualitative cues and a single quantitative cue.

Minimal information to determine affine shape equivalence.

“…Pursuing this approach, we have used a perturbation technique (Foster, 1980b) that progressively distorted pairs of same patterns, degrading each qualitatively invariant property. The results of these experiments (Kukkonen, Foster, Wood, Wagemans, & Van Gool, 1996) confirmed the special role of qualitative cues. For example, clear peaks and troughs in performance were obtained where patterns changed from parallel to nonparallel and from having collinear points to noncollinear points.…”

Formation of visual “objects” in the early computation of spatial relations

“…Nonaccidental properties do induce grouping, but only with some caveats: collinearity induces grouping only in the more general guise of relatability and Gestalt good continuation, and cotermination induces grouping only when the angle is small, again consistent with good continuation. Symmetry, by its nature a less local and more configural cue, induces grouping even after short processing times, reflecting its importance in the early computation of pattern structure (Kukkonen, Foster, Wood, Wagemans, & van Gool, 1996;Wagemans, 1997;Wagemans, van Gool, Lamote, & Foster, 2000). The interplay of cues across time is revealed particularly vividly by the data for T-junctions, which suggest that local cues dominate early while configural cues eventually override them.…”

Measuring pictorial balance perception at first glance using Japanese calligraphy

“…For example, when people see a 93° angle they perceive “an inadequate right angle”. Likewise, almost perfectly parallel lines are as likely to be perceived as parallel or as not parallel (Kukkonen et al 1996). Quasi-invariant properties such as near parallelism are influential in object recognition over novel viewpoints and rotations (Wagemans et al 2000), similar to the nonaccidental property of perfect parallelism (Biederman 1987).…”