264 • CHAPTER 9 Knowledge
Using this procedure, Paul Quinn and Mark Johnson (2000) have shown that
infants as young as 2 months of age can mentally represent a category of mammals
(such as cats, dogs, horses) that excludes furniture (such as chairs, couches, beds).
This represents categorization at the broad, global level that we discussed earlier in
the chapter (see page 247). However, infants this age don’t yet form separate catego-
ries for cats, rabbits, and dogs, so they haven’t yet formed intermediate, basic level
categories.
By 3 to 4 months of age, infants begin forming basic level categories, as indicated
by experiments like those described in the Methods section, which show that after
being familiarized with cats, infants look more at a dog than at a novel cat (Furrer
& Younger, 2005; Oakes & Ribar, 2005; Quinn et al., 1993; Younger & Fearing,
1999). This ability to categorize at the basic level is not completely developed by 3 to
4 months, however. After familiarization with cats, if infants this age are tested with
a novel cat and a novel lion, the infants do not look more at the novel lion. Thus,
while the infants can form a category “cat” that is separate from the category “dog,”
their “cat” category does not exclude lions, perhaps because lions have some catlike
qualities. Slightly older infants (6 to 7 months) do respond differently to cats and lions
(Eimas & Quinn, 1994).
At 6 to 7 months, infants can form even more specifi c categories.
● Figure 9.29 shows the results of an experiment that used the same proce-
dure as shown in Figure 9.28, except the cats in the familiarization part of
the experiment were different examples of one kind of cat (all tabbies). In
the preference test, when a new tabby cat was paired with a new Siamese,
infants looked more at the new Siamese (Quinn, 2004). This result supports
the idea that 6- to 7-month-old infants have formed categories for specifi c
types of cats.
However, just as 3- to 4-month-old infants’ capacity to categorize at the
basic level is not fully developed (their cat category was separate from dogs,
but not from lions), the 6- to 7-month-old infants’ ability to categorize at
the specifi c level is only partially developed. This is indicated by the fi nding
that when the procedure is reversed, so the infants are familiarized with
Siamese cats and then tested by presenting a Siamese and a tabby, they do
not show a preference for the tabby. Thus, 6- to 7-month-old infants can
form a category “tabby” that does not include “Siamese,” but not a category
“Siamese” that does not include “tabby.” The reason why the tabby-Siamese
experiment doesn’t work in reverse isn’t clear. The ability to distinguish
between tabby and Siamese categories in both directions develops at a later
age, although experiments determining the exact age at which this occurs
have not yet been done.
These results for infants ranging from 2 months to 7 months of age
demonstrate a progression from fi rst being able to form global categories,
then basic categories, and fi nally, specifi c categories (Quinn & Tanaka, 2007;
Younger & Fearing, 2000). Thus, categories become more “fi ne-tuned” as
infants get older.
The development of categorization does not, of course, end at 7 months.
The early development we have described sets the stage for the development
of more sophisticated concepts, a process that accelerates once language
develops. This process enables young children to begin associating specifi c
properties, such as the ones shown for the cat in Figure 9.1, with their cat-
egories. As children continue to acquire more knowledge (for example, that
cats give birth to kittens, and that kittens are born with their eyes closed), this
knowledge is incorporated into the mental representation of cats that was
initially formed during infancy. This continuing “enrichment” of concepts is
an important part of the cognitive developmental process that turns the per-
ceptual categories of infants into the more knowledge-based ones of children
and adults (Murphy, 2002; Quinn, 2008).● FIGURE 9.29 Procedure for determining
whether an infant has formed specifi c
categories for “tabby” and “Siamese.”
(a) A number of pairs of tabbies are shown
during familiarization. One pair is shown
here. (b) After the pairs of tabbies, a new
tabby is paired with a Siamese during the
preference test. Percentages indicate the
amount of time spent looking at each picture
during the preference test. (Source: Data from
Quinn, 2004. Photos ZTS, 2010/used under license
from Shutterstock.com; Paul Cotney, 2010/used
under license from Shutterstock.com; AngiePhotos/
iStockphoto.com; kovalvs/iStockphoto.com.)Looking time during
preference test39% 61%(a) Familiarization(b) Preference testCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.