Art and nature provide much of their aesthetic appeal from a balance of simplicity and complexity, and order and unpredictability. Recently, complex natural patterns have been produced by simple mathematical equations whose solutions appear unpredictable (chaotic). Yet the simplicity and determinism of the equations ensure a degree of order in the resulting patterns. The first experiment shows how aesthetic preferences correlate with the fractal dimension ( F) and the Lyapunov exponent ( L) of the patterns. F reflects the extent that space is filled and L represents the unpredictability of the dynamical process that produced the pattern. Results showed that preferred patterns had an average F = 1.26 and an average L = 0.37 bits per iteration, corresponding to many natural objects. The second experiment is a preliminary test of individual differences in preferences. Results suggest that self-reported creative individuals have a marginally greater preference for high F patterns and self-reported scientific individuals preferred high L patterns. Objective tests suggest that creative individuals had a slightly greater preference for patterns with a low F.
Research on the perception of texture gradients has relied heavily on the subjective reports of observers engaged in free-viewing. We asked whether these findings generalized to speeded performance. Experiment 1 showed that an important aspect of subjective perception-sizeconstancy scaling with perceived distance-also predicted the speed of pop-out visual search for cylinders viewed against a texture gradient. Experiment 2 showed that this finding could not be attributed to the local contrast between search items and the background texture. Experiment 3 assessed the relative contributions of 2 separable dimensions of texture gradients-perspective (radial spreading) and compression (foreshortening)-finding them to be independent in the more rapid search conditions (long target among shorter distractors) but combined in their influence in the slower conditions (short target among longer distractors).When observers view the texture gradient shown in Figure 1A they usually report seeing a flat surface recede into the distance, despite the fact that a two-dimensional (2-D) image alone cannot specify the three-dimensional (3-D) surface that gave rise to the projection. This study asked whether the factors influencing the perceived slant of such texture gradients also influences rapid visual search for objects placed on their surface.Although a large number of previous studies have examined the perception of slant in texture gradients (e.g., Flock, 1965;Gibson, 1950aGibson, , 1950bGibson, , 1979Pizlo & Rosenfeld, 1992;Stevens, 1981Stevens, , 1983aStevens, , 1983bTodd & Akerstrom, 1987;Witkin, 1981), most have relied on the subjective reports of observers. For example, observers in Gibson's (195 Ob) pioneering work matched the slant of textured surfaces in photographs by using their palms to show a corresponding inclination. The more recent studies have used variations on this method. We wondered whether the findings obtained with these measures would generalize to a performance-based measure.This question arose quite naturally from our concern for the larger issue of ecological validity. We noted that researchers who use naturalistic stimuli to study perception under ecologically valid conditions do not necessarily show the same consideration for the observer's task. Observers are typically given unlimited time to view the stimulus and to produce a slant estimate. This task is not related in any direct way to the everyday actions for which the visual system is used, ranging from those that are essential for the survival of an individual or the species (e.g., feeding, fight-
Recent reports ofrapid visual search for some feature conjunctions-suggested that preattentive vision might be sensitive to scene-based as well as to image-based features (Enns & Rensink, 1990a, 1990b. This study examined visual search for targets defined by the direction of a luminance gradient, a conjunction of luminance and relative location that often: corresponds to ob-= ject curvature and direction of lighting in naturalistic scenes. Experiment 1 showed that such search is influenced by several factors, including the type of gradient, the shape of the contour enclosing the gradient, and the background luminance. These factors were varied systematically in Experiment 2 in a three-dimensionality rating task and in a visual-search task. The factors combined interactively in the rating task, supporting the presence of an emergent property of three-dimensionality. In contrast, each factor contributed only additively to the speed of the visualsearch task. This is inconsistent with the view that search is guided by specialized detectors for surface curvature or direction of lighting. Rather, it is in keeping with the view that search is governed by a number of "quick and dirty" processes that are implemented rapidly and in parallel across the visual field.Conventional theories of preattentive vision claim that simple features such as size, orientation, luminance, and motion are registered automatically and in parallel, whereas the serial spotlight of attention is required to detect conjunctions of these features (Beck, Prazdny, & Rosenfeld, 1983;Julesz, 1984;Treisman, 1986). This claim is based on data from visual-search and texture-segmentation tasks: preattentive sensitivity is implicated by visual-search rates that are relatively independent of display size (i.e., less than 10 msec per item) and by texture boundaries that are perceived spontaneously (i.e., within 50-100 msec of display onset).Recently, there have been several reports of very rapid search andlor texture segmentation based on complex conjunctions of these features. Ramachandran (1988) showed that it is possible to segment a texture on the basis of the direction of the luminance gradients within circular texture elements; Nakayama and Silverman (1986) demonstrated rapid search for conjunctions of binocular disparity with motion and color; McLeod, Driver, and Crisp (1988) reported similar results for the conjunction of motion with shape; and Rensink (1990a, 1990b, 199 la) showed that rapid search was possible for spatial relations among lines and shaded polygons.How should these results be interpreted? Enns and Rensink (1991a, in press) suggest a framework that distinguishes between features of objects in three-dimensional This research was supported by an NSERC (Canada) grant to J.T.E. We are grateful to Ron Rensink, Steve Taylor, and Shuji Mon for comments on earlier drafts of this paper and to Lester Krueger for critical suggestions. Please address correspondence to J. T. Enns, Department of Psychology, University of British Columbia, 2136 W...
The existence of the moon illusion in pictorial representations was demonstrated in 6 experiments. Ss either judged the size of the moon in pictures, depicted as on the horizon or high in the sky, or drew horizon and elevated moons. The horizon moon was consistently judged to be larger than the elevated moon, independent of the angle at which the pictures are viewed. The distance paradox usually observed with the moon illusion (horizon moon apparently closer than the elevated moon) also exists in pictures. The magnitude of both size and distance effects depends on the salience of depicted depth cues. The pattern of results suggests that the moon illusion is caused by several interacting mechanisms and that use of pictorial stimuli may allow the separation of various cognitive from physiological contributions to the illusion.
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