Probing pictorial relief: from experimental design to surface reconstruction.

The perception of pictorial surfaces has been studied quantitatively for more than 20 years. During this time, the "gauge figure method" has been shown to be a fast and intuitive method to quantify pictorial relief. In this method, observers have to adjust the attitude of a gauge figure such that it appears to lie flat on a surface in pictorial space. Although the method has received substantial attention in the literature and has become increasingly popular, a clear, step-by-step description has not been published yet. In this article, a detailed description of the method is provided: stimulus and sample preparation, performing the experiment, and reconstructing a 3-D surface from the experimental data. Furthermore, software (written in PsychToolbox) based on this description is provided in an online supplement. This report serves three purposes: First, it facilitates experimenters who want to use the gauge figure task but have been unable to design it, due to the lack of information in the literature. Second, the detailed description can facilitate the design of software for various other platforms, possibly Web-based. Third, the method described in this article is extended to objects with holes and inner contours. This class of objects have not yet been investigated with the gauge figure task.