The awakening of Attneave's sleeping cat: identification of everyday objects on the basis of straight-line versions of outlines.

Attneave (1954 Psychological Review 61 183-193) demonstrated that a line drawing of a sleeping cat can still be identified when the smoothly curved contours are replaced by straight-line segments connecting the positive maxima and negative minima of contour curvature. Using the set of line drawings by Snodgrass and Vanderwart (1980 Journal of Experimental Psychology: Human Learning and Memory 6 174-215) we made outline versions (with known curvature values along the contour) that can still be identified and that can be used to test Attneave's demonstration more systematically and more thoroughly. In five experiments (with 444 subjects in total), we tested identifiability of straight-line versions of 184 stimuli with different selections of points to be connected (using 24 to 28 subjects per stimulus per condition). Straight-line versions connecting curvature extrema were easier to identify than those based on inflections (where curvature changes sign), and those connecting salient points (determined by 161 independent subjects) were easier than those connecting midpoints. However, identification varied considerably between objects: some were almost always identifiable and others almost never, regardless of the selection criterion, whereas identifiability depended on the specific shape attributes preserved in the straight-line version of the outline in other objects. Results are discussed in relation to Attneave's original hypotheses as well as in the light of more recent theories on shape perception and object identification.