Page 135 - Foundations of Cognitive Psychology : Core Readings

Perception 139

of perception can be thought of as the process of determining the distal stimu-
lus from information contained in the proximal stimulus. This is true across
perceptual domains. Forhearing,touch,taste,and so on,perceptioninvolves
processes that use information in the proximal stimulus to tell you about prop-
erties of the distal stimulus.
To show you how the distal stimulus and proximal stimulus fit with the three
stages in perceiving, let’s examine one of the objects in the scene from figure
7.2: the picture hanging on the wall. In the sensory stage, this picture corre-
sponds to a two-dimensional trapezoid in your retinal image; the top and bot-
tom sides converge toward the right, and the left and right sides are different in
length. This is the proximal stimulus. In the perceptual organization stage, you
see this trapezoid as a rectangle turned away from you in three-dimensional
space. You perceive the top and bottom sides as parallel, but receding into the
distance toward the right; you perceive the left and right sides as equal in
length. Your perceptual processes have developed a strong hypothesis about the
physical properties of the distal stimulus; now it needs an identity. In the rec-
ognition stage, you identify this rectangular object as a picture. Figure 7.4 is a
flowchart illustrating this sequence of events. The processes that take informa-
tion from one stage to the next are shown as arrows between the boxes. By
the end of this chapter, we will explain all the interactions represented in this
figure.

Reality, Ambiguity, and Illusions
We have defined the task of perception as the identification of the distal stim-
ulus from the proximal stimulus. Before we turn to some of the perceptual
mechanisms that make this task successful, we want to discuss a bit more some
other aspects of stimuli in the environment that make perception complex.
Once again, you should look forward to learning how your perceptual pro-
cesses deal with these complexities. We will discuss ambiguous stimuli and per-
ceptual illusions.
Ambiguity A primary goal of perception is to get an accurate ‘‘fix’’ on the
world. Survival depends on accurate perceptions of objects and events in your
environment—Is that motion in the trees a tiger?—but the environment is not
always easy to read. Take a look at the photo of black-and-white splotches in
figure 7.5. What is it? Try to extract the stimulus figure from the background.
Try to see a dalmatian taking a walk. The dog is hard to find because it blends
with the background, so its boundaries are not clear. (Hint: the dog is on the
right side of the figure, with its head pointed toward the center.) This figure is
ambiguous in the sense that critical information is missing, elements are in un-
expected relationships, and usual patterns are not apparent. Ambiguity is an
important concept in understanding perception because it shows that a single
image at the sensory level can result in multiple interpretations at the perceptual
and identification levels.
Figure 7.6 shows three examples of ambiguous figures. Each example permits
two unambiguous but conflicting interpretations. Look at each image until you
cansee thetwo alternativeinterpretations.Noticethatonceyou haveseen both
of them, your perception flips back and forth between them as you look at the