Use of preferential inspection to define the viewing sphere and characteristic views of an arbitrary machined tool part.

Measurements were made of the way human subjects visually inspected an idealized machined tool part (a 'widget') while learning the three-dimensional shape of the object. Subjects were free to rotate the object about any axis. Inspection was not evenly distributed across all views. Subjects focused on views where the faces of the object were orthogonal to the line of sight and the edges of the object were aligned parallel or at right angles to the gravitational axis. These 'face' or 'plan' views were also the easiest for subjects to bring to mind in a mental imagery task. By contrast, when subjects were instructed to imagine the views displaying the most structural information they visualized views lying midway between face views.