56 • CHAPTER 3 Perception
PERCEIVING ODOR INTENSITY:
TAKING SNIFFING INTO ACCOUNT
Imagine that you are given the following instruc-
tions: “Your task is to smell this fl ower and rate the
intensity of its odor on a scale of 1 to 10. Flowers
with very strong odors, with a fragrance you can
smell from a distance, would receive a rating near
the high end of the scale. Flowers with more subtle
odors, which can be smelled only from very close
up, would receive a rating nearer the low end of
the scale. The odor of the fl ower you are going to
smell is somewhere between these two extremes.”
Following these instructions, you bring the fl ower
to your nose and sniff. You begin with a weak sniff,
and then sniff more strongly. The question is, Would
you rate the fl ower’s odor intensity differently fol-
lowing these two different sniffs?
In a classic experiment, Robert Teghtsoonian
and coworkers (1978) asked participants in a labo-
ratory situation to rate the odor intensity of different
odorants (chemical solutions with odors) and found
that their participants gave almost identical ratings
for weak sniffs and for strong sniffs. Think about
what this means. Even though stronger sniffi ng causes more odor molecules to stimulate
the receptors, this did not infl uence the participants’ odor intensity ratings (● Figure 3.12).
Teghtsoonian and coworkers concluded from this result that their participants were tak-
ing the strength of their sniff into account in making their ratings. Does this sound famil-
iar? Just as the perceptual system takes distance and perhaps other factors into account
when a person is perceiving size, the perceptual system takes sniff intensity into account
when a person is perceiving odor intensity.
It is clear from these two very different examples that while perception may start
at the receptors, it depends on additional sources of information as well. The goal of
the perceptual system, after all, is to provide accurate information about what is out
there in the environment. This is obviously important for survival. For example, we
will know to take care when we see a large creature, even if it is far away and so casts
a small image on our retinas, and to sniff only very weakly when we might be dealing
with a potentially dangerous chemical.- What does Crystal’s run down the beach illustrate about perception? List at
least three different characteristics of perception. Why does the importance of
perception extend beyond identifying objects? - What is bottom-up processing? How can it be described physiologically?
Behaviorally? Be sure you understand the basic idea behind recognition-by-
components theory, including the role of geons and the principle of componen-
tial recovery. - Describe how the following indicate that perception involves more than
bottom-up processing: (1) naming objects created by geons; (2) multiple
personalities of a blob; (3) physiological feedback signals. Following up on
this, what is top-down processing, and how can we draw an analogy between
perception and baking bread? - Describe how the following examples show that perception involves taking
into account information in addition to what is on the receptors: (1) perceiving
size, including the examples of the creatures on the railroad tracks, the two-
quarters demonstration, and perceiving a person at two different distances;
(2) perceiving the intensity of smell stimuli with weak and strong sniffs.
TEST YOURSELF 3.1
● (^) FIGURE 3.12 (a) A weak sniff causes few molecules to stimulate
receptors inside the nose; (b) a stronger sniff increases the number
of molecules reaching the receptors. Even though the receptors are
stimulated diff erently in the two cases, the person’s rating of odor
intensity does not change.
(a) Weak sniff (b) Strong sniff
Odor
intensity
rating
Odor
intensity
rating
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