Perceptual use of nonaccidental properties.

Abstract

Under the assumption of a general viewpoint, particular image properties, such as coterminalion, straightness, and parallelism, can be used to infer, more or less reliably, the corresponding characteristics in the world. In this paper, the literature about these nonaccidcnial properties (NAPS) is reviewed to trace its historical roots, to list the properties that function as NAPs, and to discuss the psychological evidence for their detection and use. Against this background, four experiments are reviewed and four are fully described that were designed to test the perceptual use of skewed symmetry (ss), which results from orthographic projection of planar bilateral or mirror symmetry (BS). Despite the large symmetry advantage obtained in all experiments, ss is only perceived as RS-in-depth in cases of closed polygons or dot patterns with higher-order types of symmetry. In all random dot patterns and in some symmetric patterns with low "Gestalt", subjects relied on more local groupings which are qualitatively affine invariant, such as clusters based on proximity or curvilincarity. Based on previous approaches in the literature and these new findings, I suggest some distinctions between different ways of using NAPs, which might foster further research.Resume Dans I'hypothesc ou il existe un point de vuc gcncYal, il cst possible dc de'duire dc facon plus ou moins juste, a partir de ccrtaincs proprie'tes illustrees dans les images comme la cotcrmination, la rcctilignite' et lc parallelismc, les caracte>istiques correspondantes dans lc monde. Dans lc present document, on passe en revue la literature concernant les proprie'te's non accidentelles (PNA) afin d'en cxposer l'origine, d'enumcrer les proprictcs constituant des PNA et d'examiner les elements de prcuvc psychologiqucs a I'appui dc ('identification ct de I'utilisation de ccs proprietes. A la lumicrc de ces informations, quatrc experiences sont examinees, et quatre autrcs, decriies dc facon exhaustive; elles ont etc conyues pour verifier I'utilisation perceptuellc dc la symetric oblique, resultant dc la projection orthographique de la symetrie bilatcralc planaire ou spcculaire. Malgrc I'important avantagc de la symetrie qu'on a observe dans toutcs les experiences, les sujets ne percevaicnt que dc la syme'trie bilatcralc en profondcur lil oil il y avail symelrie oblique, dans le cas dc polygones fcrm6s ou de motifs de points dont 1'ordre de

The Perception of Symmetry in Depth: Effect of Symmetry Plane Orientation

“…However, the task of detecting the symmetry projected onto the x-y plane-the observer's frontoparallel plane-makes the depth variation an irrelevant property. While most perceptual studies place planar patterns normal to the visual direction, skewing the pattern by means of a rotation about a line in the x-y plane gives access to more generic vantage points [7][8][9][10][11][12][13][14][15][16][17][18][19]. After the rotation, cues to the pattern's symmetry can be indirect and more complex, for the retinal image is then typically asymmetrical.…”

Minimal information to determine affine shape equivalence.

“…Also, if the point pattern happened to have two points close together or three points almost collinear, this property was easy to verify for the other pattern: If it was also present, participants tended to respond same; if it was not, they tended to respond different (likewise for parallel configurations). Convexity, proximity, coUinearity, and parallelism are referred to as qualitative invariants (or nonaccidental properties; see Biederman, 1987;Lowe, 1987;Wagemans, 1992Wagemans, , 1993to distinguish them from the numerical invariants discussed in the preceding section. This notion may be clarified by considering the properties of convexity/concavity, parallelism, and collinearity in turn.…”

Viewpoint-invariant Weber fractions and standard contour-curvature discrimination

“…Skew transformations, which do not preserve the symmetry of the curved lines (and which have been investigated in more general studies of form perception; see Wagemans (1992Wagemans ( , 1993), are not included. The transformations of interest are therefore a proper subgroup of the group of affine transformations.…”