96 CHAPTER 3
the level of full conscious perception. Participants are not aware or conscious that
they have been exposed to the stimuli due to masking or manipulation of attention.
Furthermore, the stimuli typically influence automatic reactions (such as an increase
in facial tension) rather than direct voluntary behaviors (such as going to buy some-
thing suggested by advertising).
Another useful way of analyzing what stimuli we respond to is based on signal
detection theory. Signal detection theory is used to compare our judgments, or the deci-
sions we make, under uncertain conditions. The ability to detect any physical stimulus
is based on how strong it is and how mentally and physically prepared the individual is.
It was originally developed to help address issues associated with research participants
guessing during experiments and is a way to measure accuracy (Green & Swets, 1966;
Macmillan & Creelman, 1991).
For example, a stimulus can be either present or absent. In turn, an individual can
either detect a stimulus when present, a “hit,” or say it is not there, a “miss.” He or she
can also falsely report a stimulus as present when it actually isn’t, a “false alarm,” or cor-
rectly state it isn’t there, a “correct rejection.”Habituation and Sensory Adaptation
3.3 Explain why some sensory information is ignored.
Some of the lower centers of the brain filter sensory stimulation and “ignore” or prevent
conscious attention to stimuli that do not change. The brain is primarily interested in
changes in information. That’s why people don’t really “hear” the noise of the air con-
ditioner unless it suddenly cuts off, or the noise made in some classrooms, unless it gets
very quiet or someone else directs their attention toward it. Although they actually are
hearing it, they aren’t paying attention to it. This is called habituation, and it is the way
the brain deals with unchanging information from the environment. to Learn-
ing Objective 2.10.Sometimes I can smell the odor of the garbage can in the kitchen
when I first come home, but after a while the smell seems to go
away—is this also habituation?Although different from habituation, sensory adaptation is another process
by which constant, unchanging information from the sensory receptors is effectively
ignored. In habituation, the sensory receptors are still responding to stimulation, but the
lower centers of the brain are not sending the signals from those receptors to the cortex.
The process of sensory adaptation differs because the receptor cells themselves become
less responsive to an unchanging stimulus—garbage odors included—and the receptors
no longer send signals to the brain.
For example, when you eat, the food that you put in your mouth tastes strong at
first, but as you keep eating the same thing, the taste does fade somewhat, doesn’t it?
Generally speaking, all of our senses are subject to sensory adaptation.
You might think, then, that if you stare at something long enough, it would also
disappear, but the eyes are a little different. Even though the sensory receptors in the
back of the eyes adapt to and become less responsive to a constant visual stimulus, under
ordinary circumstances, the eyes are never entirely still. There’s a constant movement of
the eyes, tiny little vibrations called “microsaccades” or “saccadic movements,” that peo-
ple don’t consciously notice. These movements keep the eyes from adapting to what they
see. (That’s a good thing, because otherwise many students would no doubt go blind
from staring off into space.)signal detection theory
provides a method for assessing the
accuracy of judgments or decisions
under uncertain conditions; used in
RerceRtion research and other areas.
An individual’s correct “hits” and
rejections are compared against their
pmissesq and pfalse alarms.q
habituation
tendency of the Drain to stoR attending
to constant unchanging information.
sensory adaptation
tendency of sensory receptor cells to
Decome less resRonsive to a stimulus
that is unchanging.
This young woman does not feel the
piercings on her ear and nose because
sensory adaptation allows her to ignore a
constant, unchanging stimulation from the
metal rings. What else is she wearing that
would cause sensory adaptation?