262 • CHAPTER 9 Knowledge
The results of this experiment for an IT neuron are shown in Figure 9.25b.
This fi gure shows the response of the neuron to 60 percent dog stimuli and
60 percent cat stimuli. During presentation of the sample, when the monkey
is just looking at the stimuli, this neuron fi res more to the dog stimuli. During
the delay and test periods, when the monkey is holding the information about
the stimuli in memory and then making a category judgment, this neuron
responds in the same way to the dog and cat stimuli.
The results for the PF cortex neuron are shown in Figure 9.27c. During
presentation of the sample, this neuron responds slightly better to the dog
stimuli, although the difference is small and not signifi cant. During the delay,
however, the neuron fi res much more rapidly to the dog (this would corre-
spond to holding properties of the dog in working memory, see page 139).
During the test, when the monkey is making a decision, the difference in
response becomes even larger.
Freedman’s results show that different areas of the cortex respond to
different aspects of stimuli. The IT cortex, which distinguishes between
dogs and cats during presentation of the stimuli, appears to be respond-
ing to the features and shapes of the dog and cat stimuli. The PF cortex,
which distinguishes between dogs and cats during the delay and while the
monkey is making a decision, appears to be responding to more abstract
properties of the stimuli that are characteristic of dogs in general or of cats
in general.NEUROPSYCHOLOGY OF CATEGORIES
Another line of research on categorization has involved neuropsychology—
studies of the behavior of people with brain damage. Neurosychological
research on how categories are represented in the brain has focused on
patients with category-specifi c knowledge impairment, in which the patient
has trouble recognizing objects in one category. ● Figure 9.26 shows the
results for two patients, K.C. and E.W., who have diffi culty naming animals,
but can name nonliving things and fruits and vegetables (Blundo et al., 2006;
Caramazza & Shelton, 1998; Mahon & Carmazza, 2009).
These patients appeared to have problems not only in telling the dif-
ference between different animals, but also in knowing the properties of
animals. Thus, K.C. and E.W. not only had trouble naming different kinds
of animals, but also had diffi culty answering questions about animals, such
as “Does a whale have legs?” or “Are dogs domestic animals?” However,
they were able to answer similar questions about nonanimals (Mahon &
Caramazza, 2009).BRAIN SCANNING AND CATEGORIES
Differences between responses to living and nonliving things have also
been demonstrated using brain scanning in humans. ● Figure 9.27 shows
areas that are activated by looking at pictures of animals (red-yellow
areas) and by looking at pictures of tools (blue-green areas) (Chao et al.,
2002; Martin, 2007; also see Chao et al., 1999). This difference in areas
of the brain that are activated in response to animals and to tools has
also been observed when words are presented instead of pictures. Thus,
words such as crow, pigeon, and horse, which refer to living things, acti-
vate one area of the brain, and words such as fl ute, fork, and crayon,
which refer to man-made objects that people use, activate another area
(Wheatley et al., 2005).
When we consider the specifi c areas that are activated by animals and
tools, an interesting result emerges. Areas activated by animals also respond
well to the kinds of motion associated with animals, such as walking andPatient K.C. Patient E.W.020406080100Percent correct performanceNonanimals
(nonliving things,
fruits, and vegetables)Living animals●FIGURE 9.26 Performance on a naming
task for patients K.C. and E.W., both of whom
had category-specifi c knowledge impairment.
They were able to correctly name pictures
of nonliving things (like car and table) and
fruits and vegetables (like tomato and pear),
but performed poorly when asked to name
pictures of animals. (Source: B. Z. Mahon & A.
Caramazza, “Concepts and Categories: A Cognitive
Neuropsychological Perspective,” Annual Review of
Psychology, 60, 27–51, Figure 1, 2009. Reprinted by
permission.)● FIGURE 9.27 Cross section of the brain,
looking up from the bottom, showing brain
activation measured by fMRI. Yellow-red
areas were activated by naming pictures of
animals; blue-green areas were activated by
naming pictures of tools. (Source: A. Martin, “The
Representation of Object Concepts In The Brain, Annual
Review of Psychology, 58, 25–45, 2007.)Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.