Overestimation of the projected size of objects on the surface of mirrors and windows.

Rebecca Lawson, University of Liverpool

Marco Bertamini, University of Liverpool

Dan Liu, Shaanxi Normal University

Four studies investigated people’s judgements of the size of projections of objects on the glass surface of a mirror or of a window. We tested different ways of explaining the task to overcome the difficulty that people have in understanding what the projection of an object is, and we varied the distance of the observer and the object to the mirror or window and the size of the mirror. We compared estimations of projected size to estimations of the physical size of the object that produced the projection. For both mirrors and windows, observers could accurately judge the physical size of objects but they greatly overestimated the projected size of the same objects. Judgements of projected size were more similar to physical than to projected size and were generally 60% or more too large. People were also questioned verbally about their knowledge of projected size relative to physical size. Similar errors were produced for these conceptual questions as were found in the perceptual estimation tasks. Together these results suggest that projections of objects on mirrors and windows are treated in the same way, and that observers cannot perceive such projections as distal objects.

Journal of Experimental Psychology: Human Perception and Performance, (2007), 33, 1027-1044.