Picasso in the mind's eye of the beholder: three-dimensional filling-in of ambiguous line drawings.

Cartoon-style line drawings contain very condensed information, after all most of the page stays blank. Yet, they constrain the contents of immediate visual awareness to an extraordinary extent. This is true even for drawings that are - though nominally "representational" - not even in central projection. Moreover, the strokes used in a drawing may stand for a bewildering variety of entities in the world. We studied Picasso drawings from the 1940s in which the artist famously combined multiple viewpoints. We find that the pictorial reliefs obtained from various observers agree to a large extent, and that the differences are of a very specific nature, typically involving variations in the mutual spatial attitudes of rigid body parts in figure studies. Although the purely planar layout of the drawings accounts for much of visual awareness, observers also use the sparse depth cues provided by the artist to evoke volumetric impressions. Observers also freely insert "template knowledge" about the structure of familiar generic objects.