Abstract
To classify objects, we compare them to mental representations of things we've seen before. By extracting objects’ shape features our visual system can map them into a mental shape space and compare their positions in that space. For example, if a stimulus falls within reasonable distance of the distribution of previously seen triangles, we tend to classify it as a triangle. To understand these classification decisions, we must understand the distribution of class members (e.g., of triangles) in our mental shape space. However, because of the enormous variety in shapes across and within object classes, it is difficult if not impossible to map out these distributions by probing individual objects (e.g., by asking “Is this shape a triangle?”). Here, we analyze drawings from Google’s “Quick, Draw!” database, which were contributed by volunteers from countries all over the world. Specifically, we looked at drawings where participants were instructed to “draw a triangle” or “draw a bread” (> 120,000 drawings each). By simplifying these drawings to their basic geometric form (best-fitting triangle, rectangle, or ellipse), we could express each drawing as a combination of just a few geometric parameters (e.g., angles, axis ratios etc.). We compared the distributions as well as their modes (i.e., the “typical triangle” and “typical bread”) in the resulting shape parameter spaces across countries. For triangles, we obtain very similar distributions of shapes with the typical triangle being equilateral. For bread, however, we obtain markedly different distributions of shapes for different countries (e.g., more rectangular, square toast in the United States and United Kingdom versus more elliptic, elongated loaves in Germany and Poland). This illustrates how we can use drawings to map out mental shape spaces, and test for the universality of object classes across different regions of the world.