Academic journal article Attention, Perception and Psychophysics

Concept Formation and Categorization of Complex, Asymmetric, and Impossible Figures

Academic journal article Attention, Perception and Psychophysics

Concept Formation and Categorization of Complex, Asymmetric, and Impossible Figures

Article excerpt

Published online: 13 June 2014

# The Psychonomic Society, Inc. 2014

Abstract Impossible figures are striking examples of inconsistencies between global and local perceptual structures, in which the overall spatial configuration of the depicted image does not yield a coherent three-dimensional object. In order to investigate whether structural "impossibility" is an important perceptual property of depicted objects, we used a category formation task in which subjects were asked to divide pictures of shapes into groups that seemed most natural to them. Category formation is usually unidimensional, such that sorting is dominated by a single perceptual property, so this task can serve as a measure of which dimensions are most salient. In Experiment 1, subjects received sets of 12 line drawings consisting of six possible and six impossible objects. Very few subjects grouped the figures by impossibility on the first try, and only half did so after multiple attempts at sorting. In Experiment 2, we investigated other global properties of figures: symmetry and complexity. Subjects readily sorted objects by complexity, but seldom by symmetry. In Experiment 3, subjects were asked to draw each of the figures before sorting them, which had only a minimal effect on categorization. Finally, in Experiment 4, subjects were explicitly instructed to divide the shapes by symmetry or impossibility. Performance on this task was perfect for symmetry, but not for impossibility. Although global properties of figures seem extremely important to our perception, the results suggest that some of these cues are not immediately obvious or salient for most observers.

Keywords 2-D,3-D .Shapeperception .Objectrecognition . Impossible figures . Categorization . Concept formation

Artists, mathematicians, scientists, and philosophers have long pondered the nature of the mechanisms underlying our ability to detect and integrate the numerous bits of visual information that ultimately give way to a perception of struc- tural coherence, or lack thereof. The mature visual system may be specially tuned for processing objects, both real and depicted, in a globally coherent three-dimensional (3-D) fash- ion. This remarkable capacity enables us to readily recognize and classify a myriad of patterns and shapes. The perception of global 3-D shape arises from the extraction of critical contour information and the spatial integration of local lines, junctions, edges, and other surface characteristics (Biederman, 1987;Biederman&Ju,1988; Marr & Nishihara, 1978).

The perception of 3-D structure is saliently illustrated by the case of impossible figures. Human observers generally respond differently toward, and show increased interest in, pictures of impossible objects, and these observations have further illuminated the nature of visual processing and object representations. When looking at an image, the visual system needs to ascertain whether all of the parts add up to a globally coherent whole. Impossible figures (like those shown in Fig. 1a) tend to attract our attention and pique our interest for extended periods of time, as we try to resolve the compo- nents. Each part of an impossible figure in isolation is locally possible, but the adjoining parts do not yield a coherent real object-that is, it cannot be rendered in three dimensions out of solid, continuous material.1 The apparent differences be- tween possible and impossible shapes are generally assumed to be quite obvious and noticeable among sighted people, yet little is known about our conceptual understanding of such objects. For this reason, impossible objects provide an inter- esting way of investigating the nature of coherent object representations, as well as the conceptual understanding of structural possibility versus impossibility.

Recent studies have shown that young infants can differ- entiate between possible and impossible figures, an ability that requires analyzing local pictorial depth information and inte- grating the global spatial relations that lead to perceiving coherent 3-D objects. …

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