Fig.5.3 Preparation of stimuli in the
Rosinski et al. (1980) experiments. (1) Frontal view of photographed
object. (2) Top view of object, at 60° slant, and of camera. (3)
Frontal view of perspective photograph of object at 6o° slant.
To prove Pirenne's thesis, one must show that (a) when
the surface of a picture is hard to perceive, the virtual space of the picture
is perceived in accordance with geometric expectations; and (b) when the surface
of the picture can be seen, the virtual space of the picture is perceived to
be invariant despite changes in the observer's vantage point.
Rosinski and his colleagues performed two experiments that provide exactly these
sorts of data (Rosinski et al., 1980; see also Rosinski and Farber, 1980). shows
how the stimuli were created. Figure 5.3 shows how stimuli were created. In
panel 1, we see the object. Thirteen different photographs of this object were
taken, as shown in panel 2; each was taken at a different angle of slant. In
panel 3, we see one of these photographs appropriately cropped and mounted on
flat black matte board. In Figure 5.4, we can see the apparatus used in the
Fig.5.4 Presentation of stimuli in the
Rosinski et al. (1980) experiments. (1) Experiment 1: Information
regarding picture surface is minimized. (2) Experiment 2: Information
regarding picture surface is not reduced.
In the first experiment, Rosinski et al. simulated Brunelleschi's
peepshow. They minimized the amount of information the observer would receive
regarding the location of the picture plane by using a latter-day perspective-cabinet
with two peepholes: One peephole afforded a line of sight perpendicular to the
surface of the photograph displayed in it; the other peephole shifted the observer's
line of sight so that it formed a 45° angle with the surface of the photograph.
To further reduce the visibility of the surface of the picture, Rosinski et
al. put cross-polarized filters into the viewing box to minimize the amount
of glare by diffusing the light reflected by the surface of the photograph.
The observer would be asked to view the photograph through a peephole at the
center of projection, so that his or her line of sight would be perpendicular
to the picture plane, or through a peephole from which the observer's line of
sight would form a 45° angle with the picture plane (both were 50 cm or
just under 20 in. from the picture plane). The observer's task was to adjust
a palm board that could be rotated about a vertical pivot to indicate the perceived
slant of the plane represented in the photograph.
In the second experiment, Rosinski et al. made no attempt
to conceal the location of the picture plane, and therefore no viewing box was
used: Observers were positioned 45° to the right or 45° to the left
of the center of projection, 50 cm away from the picture plane. The picture
was viewed binocularly and the frame of the picture was visible.