Summary: A typical adult makes hundreds of categorization judg-
ments every day. Almost all of these are automatic. When
we sit in a chair, pick up a book, or swerve to avoid a pot-
hole, we are making an automatic categorization judgment.
Adults sometimes make categorization decisions that are
not automatic. For example, a dog owner might be learn-
ing to differentiate between Briards and Bouviers. Nev-
ertheless, for most adults, categorization decisions based
on newly acquired knowledge are far less common than
categorization decisions made automatically. Despite this
imbalance, initial category learning has been investigated
much more extensively than categorization automaticity.
For example, a search of PsycINFo yields 4,655 articles
in response to the keywords "category or categorization
learning," but only 57 articles in response to "category or
categorization automaticity"--a ratio of 82 to 1.
Despite the many studies that have examined the abil-
ity of people to learn new perceptual categories, we know
of only a few that have trained participants for more than
a session or two on novel categories. In all of these, par-