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Local shape of pictorial relief
Jan Koenderink1, Andrea van Doorn2, Johan Wagemans3
1Laboratory 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;
I-Perception
|December 4, 2014
Summary
Visual perception of pictorial relief is not a depth map but local surface shape. Observers reliably categorize shapes like caps, ridges, and saddles, though individual differences exist.
Area of Science:
- Visual perception
- Psychophysics
- Computational geometry
Background:
- Pictorial relief representation in visual awareness is debated.
- Previous models suggest depth maps or local surface attitudes.
- Geometric invariants offer an alternative framework for shape representation.
Purpose of the Study:
- To investigate if observers represent local surface shape from images.
- To determine the reliability and consistency of shape categorization.
- To explore inter-observer variability in shape perception.
Main Methods:
- Observers categorized local surface shape from images of sculpture.
- A five-point categorical scale (cap, ridge, saddle, rut, cup, flat) was used.
- Inter-observer consistency and judgment dispersion were analyzed.
Main Results:
- Observers reliably categorized local surface shapes with high self-consistency.
- The shape index scale (cap-ridge-saddle-rut-cup) was fully resolved.
- Significant inter-observer differences were observed, with peak dispersion at the saddle category.
Conclusions:
- Visual awareness can represent local surface shape, not just depth or attitude.
- Categorical judgments of shape are reliable but show individual variability.
- The prominence of the saddle category in judgment dispersion may relate to historical omissions in shape catalogs.
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