Evaluation It would be unwise to attach much significance to the percentages
of the various kinds of action slips for a number of reasons. First, the figures are
based on those action slips that were detected, and we simply do not know
how many cases of each kind of slips went undetected. Second, the number of
occurrences of any particular kind of action slip is meaningful only when we
know the number of occasions on which that kind of slip might have occurred
but did not. Thus, the small number of discrimination failures may reflect
either good discrimination or a relative lack of situations requiring anything
approaching a fine discrimination.
Another issue is that two action slips may appear to be superficially similar,
and so be categorised together, even though the underlying mechanisms are
different. For example, Grudin (1983) conducted videotape analyses of substi-
tution errors in typing involving striking the key adjacent to the intended key.
Some of these substitution errors involved the correct finger moving in the
wrong direction, whereas others involved an incorrect key being pressed by the
finger that normally strikes it. According to Grudin (1983), the former kind of
error is due to faulty execution of an action, whereas the latter is due to faulty
assignment of the finger. We would need more information than is generally
available in most diary studies to identify such subtle differences in underlying
processes.
Laboratory Studies of Action Slips
Several techniques have been used to produce action slips in laboratory con-
ditions. What is often done is to provide a misleading context which increases
the activation of an incorrect response at the expense of the correct response.
Reason (1992) discussed a study of the ‘‘oak–yolk’’ effect illustrating this ap-
proach. Some subjects were asked to respond as rapidly as possible to a series
of questions (the most frequent answers are given):
Q: What do we call the tree that grows from acorns?
A: Oak.
Q: What do we call a funny story?
A: Joke.
Q: What sound does a frog make?
A: Croak.
Q: What is Pepsi’s major competitor?
A: Coke.
Q: What is another word for cape?
A: Cloak.
Q: What do you call the white of an egg?
A: Yolk.
The correct answer to the last question is ‘‘albumen.’’ However, 85% of these
subjects gave the wrong answer because it rhymed with the answers to the
previous questions. In contrast, of those subjects only asked the last question, a
mere 5% responded ‘‘yolk.’’
Although it is possible to produce large numbers of action slips under labo-
ratory conditions, it is not clear that such slips resemble those typically found
390 Michael W. Eysenck and Mark T. Keane