Angle-Based Drawing Accuracy Analysis and Mental Models of Three-Dimensional Space

Abstract

Drawing from a still-life is a complex visuomotor task. Nevertheless, experts depict three-dimensional subjects convincingly with two-dimensional images. Studies of drawing have historically relied on human critics’ judgement of the drawings, the professional reputations and self-reported experience of the drawers. To extend that work, we developed an objective measurement of the accuracy of a perspective drawing, based on a comparison of the drawing with a ground truth photograph of the subject taken from the same viewpoint. If we measure the angles at intersecting edges in the drawings we can calculate both local errors and each person’s mean percentage magnitude error across angles in the still life. This gives a continuous objective measure of drawing accuracy that correlates well with years of art experience. Drawing expertise may depend to some extent on more accurate internal models of 3D space. To explore this possibility we had adults with a range of drawing experience draw a still life. Participants also made perceptual judgements of still lifes, both from direct observation and from an imagined side view. A conventional mental rotation task failed to differentiate drawing expertise. However, those who drew angles more accurately were also significantly better judges of slant, i.e., the pitch of edges in the still life. Those with the most drawing experience were significantly better judges of spatial extent, i.e., which landmarks were leftmost, rightmost, nearest, farthest etc. The ability to visualize in three dimensions the orientation and relationships of components of a still life predicts drawing accuracy and expertise.