Perceptual Organization 193tocoordinate systemsin analytic geometry (Palmer, 1989).
Reference frame effects generally show that the reference
frame for a given visual element is defined by the next-higher
element in the perceptual part-whole hierarchy. In this sec-
tion, reference frame effects in orientation and shape percep-
tion are briefly considered. Analogous effects are also present
in motion perception, but these are discussed in the chapter
by Proffitt and Caudek in this volume.
Orientation Perception
One of the most compelling demonstrations of reference
frame effects on orientation perception occurs when you
enter a tilted room, like the ones in a fun house or mystery
house of an amusement park. Although you notice the slant of
the floor as you first enter, you rapidly come to perceive the
room as gravitationally upright. After this misperception
occurs, all sorts of other illusions follow. You perceive the
chandelier as hanging at a strange angle from the ceiling, for
example, and you perceive yourself as leaning precariously
to one side, despite the fact that both the chandelier and you
are, in fact, gravitationally upright. If you try to correct your
posture to align yourself with the orientation of the room, you
may lose your balance or even fall.
Normally, the vertical orientation in the reference frame of
the large-scale visual environment coincides with gravita-
tional vertical, because the dominant orientations of per-
ceived objects—due to walls, floors, tree trunks, the ground
plane, standing people, and so forth—are either aligned with
gravity or perpendicular to it. The heuristic assumption that
the walls, floor, and ceiling of a room are vertical and hori-
zontal thus generally serves us well in accurately perceiving
the orientations of objects. When you walk into a tilted room,
however, this assumption is violated, giving rise to illusions
of orientation. The visual reference frame of the room, which
is out of alignment with gravity, captures your sense of
upright. You then perceive yourself as tilted because your
own bodily orientation is not aligned with your perception of
upright.
One particularly well-known reference frame effect on
orientation perception is the rod and frame effect(Asch &
Witkin, 1948a, 1948b). Subjects were shown a luminous rod
within a large, tilted, luminous rectangle and were asked to
set the rod to gravitational vertical. Asch and Witkin found
large systematic errors in which subjects set the rod to an
orientation somewhere between true vertical and alignment
with the frame’s most nearly vertical sides. Several experi-
ments show that the effect of the frame is greatest when the
rectangle is large, and that small ones just surrounding the
line have little effect (Ebenholtz, 1977; Wenderoth, 1974).
Other studies have shown that when two frames are present,
one inside the other, it is the larger surrounding frame
that dominates perception (DiLorenzo & Rock, 1982). These
facts are consistent with the interpretation that the rectan-
gle in a rod and frame task induces a visual frame of refer-
ence that is essentially a world surrogate, so to speak, for the
visual environment (Rock, 1990). By this account, a visual
structure will be more likely to induce a frame of reference
when it is large, surrounding, and stable over time, like the
tilted room in the previous example.Shape PerceptionBecause perceived shape depends on perceived orientation,
robust reference frame effects also occur in shape perception.
One of the earliest, simplest, and most elegant demonstra-
tions of this fact was Mach’s (1914/1959) observation that
when a square is rotated 45°, people generally perceive it as
an upright diamond rather than as a tilted square. This figure
can be perceived as a tilted square if the flat side at 45° is
taken to be its top. But if the upper vertex is perceived as the
top, the shape of the figure is seen as diamond-like and quite
different from that of an upright square.
This relation suggests that the shape of an object should
also be influenced by the orientation of a frame of reference,
and this is indeed true. One of the earliest and most com-
pelling demonstrations was provided by Kopferman (1930),
who showed that a gravitational diamond is perceived as a
square when it is enclosed within a 45° tilted rectangle.
Palmer (1985) later extended Kopferman’s discovery to other
factors that Palmer had previously shown to influence orien-
tation perception in the perceived pointing of ambiguous,
equilateral triangles, factors such as the orientation of config-
ural lines, the width and orientation of textural stripes, and
the direction of rigid motion (Palmer & Bucher, 1982;
Bucher & Palmer, 1985). In all of these cases, the claim is
that the contextual factors induce a perceptual frame of refer-
ence that is aligned along the 45° axis of the diamond and that
the shape of the figure is then perceived relative to that orien-
tation, leading to the perception of a tilted square rather than
an upright diamond.
Rock (1973) showed that such reference frame effects on
shape perception are much more general. He presented sub-
jects with a sequence of amorphous, novel shapes in a par-
ticular orientation during an initial presentation phase. He later
tested their recognition memory for the figures in the same
versus a different orientation (see Figure 7.17; A). The results
showed that people were far less likely to recognize the shapes
if they were tested in an orientation different from the original
one. This poor recognition performance, which approached