Detection of symmetry in tachistoscopically presented dot patterns: Effects of multiple axes and skewing

Abstract

We examined the effects of multiple axes and skewing on the detectability of symmetry in tachistoscopically presented (lOO-msec) dot patterns to test the role of normal grouping processes based on higher order regularities in element positions. In addition to the first-order regularities of orientational uniformity and midpoint collinearity (Jenkins, 1983), bilateral symmetry (BS) gives rise to second-order relations between two pairs of symmetric elements (represented by correlation quadrangles). We suggest that they allow the regularity (i.e., BS) to emerge simply as a result of the position-based grouping that takes place normally, so that no special symmetrydetection mechanism has to be postulated. In combination with previously investigated variablesnumber and orientation of axes-we introduced skewing (resulting from orthographic projection of BS) to manipulate the kind and number of higher order regularities. In agreement with our predictions, the data show that the effect of skewing angle (varied at three 15 0 steps, clockwise and counterclockwise) on the preattentive detectability of symmetry (measured with d') increases as the number of axes decreases. On the basis of some more specific findings, we suggest that it is not as much the number of correlation quadrangles that determines the saliency of a regularity as it is the degree to which they facilitate or "bootstrap" each other.During the time since Mach's (1886/1959) observations on the special status of bilateral or mirror symmetry for the human perceptual system, numerous experiments have been done on its detection and use. With respect to the latter, abundant data indicate the influence of symmetry on several perceptual and cognitive processes, such as scanning, encoding, short-term memory, recognition, representation, imagination, the establishment of a reference frame, and judgments of numerosity, complexity and goodness, or aesthetic value (see, e.g., Chipman

Visual signalling by asymmetry: a review of perceptual processes

“…As the general property of symmetry can be assessed by the human visual system very quickly (in less than 100 ms in some instances) (e.g. Julesz 1971;Hogben et al 1976;Carmody et al 1977;Barlow & Reeves 1979;Locher & Nodine 1989;Wagemans et al 1991Wagemans et al , 1993, it is di¤cult to explain how the pre-attentive phase accomplishes this in such a short period of time. It is possible that only part of an image is processed (e.g.…”

Toward a better approach to goodness: Comments on Van der Helm and Leeuwenberg (1996).

“…Thus, bootstrapping is not possible anymore. These properties of the BM allow an explanation of the superior detectability of orthofrontal mirror symmetry as compared with skewed symmetry (Wagemans et al, 1991;Wagemans, Van Gool, & d'Ydewalle. 1992), of double mirror symmetry as compared with single mirror symmetry (Palmer & Hemenway, 1978;Wagemans et al, 1991) and of the smaller effect of skewing with multiple symmetries (Wagemans et al, 1991).…”

“…These properties of the BM allow an explanation of the superior detectability of orthofrontal mirror symmetry as compared with skewed symmetry (Wagemans et al, 1991;Wagemans, Van Gool, & d'Ydewalle. 1992), of double mirror symmetry as compared with single mirror symmetry (Palmer & Hemenway, 1978;Wagemans et al, 1991) and of the smaller effect of skewing with multiple symmetries (Wagemans et al, 1991). Similar goodness differences in other types of dot patterns (e.g., with translational or rotational symmetry) can also be attributed to the presence or absence of higher-order regularity in correlation quadrangles such as trapezoids and parallelograms (see Wagemans et al, 1993).…”

“…Before presenting Van der Helm and Leeuwenberg's critique on me BM and my rebuttal, I briefly summarize the model's principles (for more details, see Wagemans, Van Gool, & d'Ydewalle 1991;Wagemans, Van Gool, Swinnen, & Van Horebeek, 1993) Summary of the BM. The BM is a process model that starts from the available information hi a dot pattern (i.e., the locations of the dots).…”

Asymmetry for Symmetry: Right-Hemispheric Superiority in Bi-Dimensional Symmetry Perception

“…Some evidence has been collected concerning such a bias, showing that the human visual system detects symmetry more easily than asymmetry. First of all, symmetry detection is faster than asymmetry detection [49] and it affects the performance of observers even when it is not crucial for the task [50], as well as when the symmetrical arrangement constitutes the distracters during a visual search task [51]. Finally, it has been shown that symmetry is detected before eye movements are made towards a symmetric object, meaning that symmetry detection occurs also in the absence of overt attention [52].…”