Page 149 - Foundations of Cognitive Psychology : Core Readings

Perception 153

Phenomena like this one suggest that selective attention works in two ways.
First, your internal representations of the stimuli on which you have focused
attention become highlighted in memory. Second, your internal representa-
tions of the unattended stimuli are somewhat suppressed. You can see how
these processes of highlighting and suppression will make the attended objects
specifically prominent in your consciousness. You can also see why it’s danger-
ous to let yourself become distracted from your immediate task or goal. If you
fail to pay attention to some body of information—your professor’s lecture,
perhaps—you may find it extra hard to catch up later. Let’s turn now to the
role attention plays in allowing you to find and correctly identify objects in
your environment.

Attention and Objects in the Environment
One of the main functions of attention is to help you find particular objects in a
noisy visual environment. To get a sense of how this works, you can carry out a
very simple experiment. Put your book down for a minute and look for two
things: a red object and a red object in the shape of a circle. Did it seem to you
that you could find a red object almost instantly—without having to look at
each part of the room—while finding the red circle required you to look around
the room object by object? You have just discovered the difference between
preattentive processing and processing that requires attention. We will now ex-
pand on these differences.
Preattentive Processing and Guided Search Even though conscious memory and
recognition of objects require attention, quite complex processing of informa-
tion goes on without attention and without awareness. This earlier stage of
processing is called preattentive processing because it operates on sensory inputs
before you attend to them, as they first come into the brain from the sensory
receptors. The simple demonstration in figure 7.12 gives you a rough idea of
what can and cannot be processed without attention (adapted from Rock &
Gutman, 1981). Your memory for the attended (red) shapes in the figure is
much better than memory for the unattended shapes. However, you remember
some basic features of the unattended shapes, such as their color and whether
they were drawn continuously or had gaps. It is as though your visual system
extracted some of the simple features of the unattended objects but never quite
managed to put them together to form whole percepts.
Preattentive processing is quite skilled at finding objects in the environment
that can be defined by single features (Treisman & Sato, 1990; Wolfe, 1992).
Look at part A of figure 7.13. Can you find the white T? This is a comparable
exercise to finding a red object in the room around you. Preattentive processing
allows you to search the environment in parallel for a single salient feature. This
meansthatyou cansearchall locationsinthe displayatthe same time:asa
product of this parallel search, your attention is directed to the one correct
object.
Now consider part B of figure 7.13. Try, once again, to find the white T.
Didn’t it feel harder? In this case, your attentional system is not equipped to
differentiate white T’s from white L’s in a parallel search. You can still use your
capability for parallel search to ignore all the black T’s, but you must then