Abstract
Despite the large number of shape-from-shading studies, the degree of veridicality
with which observers perceive real 3D objects from shading cues has not been
examined. Six observers viewed semicircular, triangular and trapezoidal corrugations
in depth made from gray cardboard of approximately uniform reflectance, presented
in a fronto-parallel plane. The object, placed inside a box, was illuminated solely
from its top-left or left by a point light source. The corrugations were seen through
an aperture that masked their terminating contours and the light source. Observers
were asked to draw the depth profile of the object as if it were seen from above.
Using a computer mouse, they drew on a computer screen placed just below the
object. They also indicated the orientation of the object and the location of the light
source. In the first condition, the objects were viewed monocularly; in the second, a
white matte sphere was placed in front of the objects to help in locating the light; in
the third, the task was repeated with binocular viewing. Drawings revealed that
observers were quite accurate in inferring the objects’ shapes when viewing
binocularly. There was more variability among the observers when objects were
viewed monocularly, with some systematic trends: 1. Most observers were able to
recreate the veridical shapes despite monocular viewing. 2. The drawn shapes often
differed from the shape of the luminance variations across the objects, thus rejecting
heuristics such as “dark is deeper”. 3. In the absence of cues to light direction,
observers did not tend to resort to a “light from above” prior. 4. While binocularity
heavily aided the extraction of the true shapes, knowledge of the illuminant
direction did not. However, even though the exact location of the light source did
not aid in extracting 3D shape, when oriented at a horizontal level, the light source
did aid in perceiving 3D orientation.
Description
In partial satisfaction of the requirements for the degree of Master of Science In Vision Science
State University of New York
State College of Optometry