proximal) elements are grouped together. The Gestaltists interpreted such re-
sults to mean that the whole stimulus pattern is somehow determining the or-
ganizationofitsownparts;inotherwords,thewhole perceptis different from
the mere collection of itsparts.
In D, the color of the dots instead of their spacing has been varied. Although
there is equal spacing between the dots, your visual system automatically
organizesthisstimulusintorowsbecauseoftheirsimilar color.You see the dots
in E as being organized into columns because ofsimilar size,and you see the
dots in F as being organized into rows because ofsimilar shapeandorientation.
These grouping effects can be summarized by thelaw of similarity:all else being
equal, the most similar elements are grouped together.
When elements in the visual field are moving, similarity of motion also pro-
duces a powerful grouping. Thelaw of common fatestates that, all else being
equal, elements moving in the same direction and at the same rate are grouped
together. If the dots in every other column of G were moving upward, as indi-
cated by the blurring, you would group the image into columns because of
their similarity in motion. You get this effect at a ballet when several dancers
move in a pattern different from the others. Remember Dr. Richard’s observa-
tion that an object in his visual field became organized properly when it moved
as a whole. His experience was evidence of the powerful organizing effect of
common fate.
Is there a more general way of stating the various grouping laws we have
just discussed? We have mentioned the law of proximity, the law of simi-
larity, the law of common fate, and the law of symmetry, or figural goodness.
Gestalt psychologists believed that all of these laws are just particular exam-
ples of a general principle, thelaw of pragnanz(pragnanztranslates roughly
to ‘‘good figure’’): you perceive the simplest organization that fits the stimulus
pattern.
Spatial and Temporal Integration
All the Gestalt laws we have presented to you so far should have convinced
youthatalotofperceptionconsistsofputtingthepiecesofyourworldto-
gether in the ‘‘right way.’’ Often, however, you can’t perceive an entire scene in
one glance, orfixation(recall our discussion of attention). What you perceive at
a given time is often a restricted glimpse of a large visual world extending in all
directions to unseen areas of the environment. What may surprise you is that
your visual system does not work very hard to create a moment-by-moment,
integrated picture of the environment. Research suggests that your visual
memory for each fixation on the world does not preserve precise details (Irwin,
1991). Why is that so? Part of the answer might be that the world itself is gen-
erally a stable source of information (O’Regan, 1992). It is simply unnecessary
to commit to memory information that remains steadily available in the exter-
nal environment.
One interesting consequence of the way you treat the information from dif-
ferent fixations is that you are taken in by illusions called ‘‘impossible’’ objects,
such as those in figure 7.22. For example, each fixation of corners and sides
provides an interpretation that is consistent with an object that seems to be a
three-dimensional triangle (image A); but when you try to integrate them into a
Perception 163