Depicted angle of forms and perception of line drawings

Subjects were presented with projections of either rectangular or elliptic forms which appeared either on their own or upon the following figures: (a) a face of a portrayed cube, (b) a parallelogram identical with (a), and (c) a rectangle of equal width and area to (a). Four different angles of projection were used for both the forms and for the background figures. In the composite figures these angles were varied independently. The subjects were required to judge the width of the forms. The forms were judged to be wider when presented on backgrounds (a) and (b) than when presented on background (c) or alone, especially at greater angles of projection. This suggests that the implicit-shape constancy effect is independent of relational effects resulting from the frame surrounding the form.