title: Local shape of pictorial relief.
abstract: How is pictorial relief represented in visual awareness? Certainly not as a "depth map," but perhaps as a map of local surface attitudes (Koenderink & van Doorn, 1995). Here we consider the possibility that observers might instead, or concurrently, represent local surface shape, a geometrical invariant with respect to motions. Observers judge local surface shape, in a picture of a piece of sculpture, on a five-point categorical scale. Categories are cap-ridge-saddle-rut-cup-flat, where "flat" denotes the absence of shape. We find that observers readily perform such a task, with full resolution of a shape index scale (cap-ridge-saddle-rut-cup), and with excellent self-consistency over days. There exist remarkable inter-observer differences. Over a group of 10 naive observers we find that the dispersion of judgments peaks at the saddle category. There may be a relation of this finding to the history of the topic-Alberti's (1827) omission of the saddle category in his purportedly exhaustive catalog of local surface shapes.
authors.affiliation: Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Tiensestraat 102, Box 3711, B-3000 Leuven, Belgium; and Faculteit Sociale Wetenschappen, Psychologische Functieleer, Universiteit Utrecht, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands; e-mail: Jan.Koenderink@ppw.kuleuven.be.
authors.forename: Jan
authors.initials: J
authors.lastname: Koenderink
authors.affiliation: Faculteit Sociale Wetenschappen, Psychologische Functieleer, Universiteit Utrecht, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands; e-mail: andrea.vandoorn@telfort.nl.
authors.forename: Andrea
authors.initials: A
authors.lastname: van Doorn
authors.affiliation: Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Tiensestraat 102, Box 3711, B-3000 Leuven, Belgium; e-mail: Johan.Wagemans@psy.kuleuven.be.
authors.forename: Johan
authors.initials: J
authors.lastname: Wagemans
keywords: depth perception; picture perception; shape perception; shape scale; surface perception