506 Procedural Memory and Skill Acquisition
actual performance may be most important during learning
of a novel motor task. Both positron-emission tomography
(PET) and functional magnetic resonance imaging (fMRI)
data are compatible with the idea that the cerebellum is
heavily involved when movement errors are common and
corrective movements must be produced to compensate
for them. Cerebellar activity decreases as skill increases,
and there is a positive correlation between the number of
errors and cerebellar activity. Interestingly, several studies
have shown a decrease in cerebellar activity as a function
of the learning of finger-movement sequences (e.g., Friston,
Frith, Passingham, Liddle, & Frackowiak, 1992). Increased
activity in motor cortical areas during motor learning indi-
cates that these areas also contribute to the learning
process, and neuroimaging studies point to a role of pri-
mary and secondary motor cortex in learning tasks such as
the SRT task.
PROCEDURAL MEMORY, IMPLICIT LEARNING,
AND SKILL
Most scholars would agree that the distinction between pro-
cedural and explicit, episodic memory is a real one, and that
different systems underlie implicit and explicit remembering.
The exact nature of the relationship between implicit and
explicit learning is less clear. Some have argued that im-
plicit knowledge provides the basis for explicit knowledge
(Ziessler, 1998), others have argued that explicit knowledge
is converted into procedural knowledge (Anderson, 1983),
and still others have argued that implicit and explicit knowl-
edge develop independently of each other (Willingham &
Goedert-Eschmann, 1999). Studies using PET imaging are
consistent with the idea that explicit and implicit learning
have separate foundations. Grafton, Hazeltine, and Ivry
(1995; Hazeltine, Grafton, & Ivry, 1997), for example, found
metabolic changes in primary and supplementary motor
cortexes and the putamen that were associated with implicit
learning, whereas explicit learning was associated with
changes in blood flow in prefrontal and premotor cortices.
Willingham and Goedert-Eschmann used transfer tasks to
show that the degree of implicit learning in an SRT task did
not depend on whether explicit learning instructions were
given. This suggests that implicit learning is indeed indepen-
dent of explicit learning and that performance that is initially
dominated by conscious mediation may eventually come to
rely on implicit knowledge that has quietly been developing
as a direct by-product of task performance. However, further
work is necessary to determine the way in which implicit and
explicit learning are related.
SKILLED PERFORMANCEProctor and Dutta (1995) defined skill as “goal-directed, well-
organized behavior that is acquired through practice and
performed with economy of effort” (p. 18). Thus, all skills are
assumed to be acquired through practice or training, to be the
result of goal-directed learning (even though incidental learn-
ing may occur as the result of performance), and to be ex-
pressed in coordinated, efficient performance. Simple skills,
such as performing SRT tasks, consist of only a few basic com-
ponents (perception, classification, response selection, and
response) and are learned after a relatively modest amount of
practice. Complex skills, such as solving physics problems, are
made up of multiple components that need to be learned and in-
tegrated before skill is acquired. Such skills take more time to
develop and are more dependent on the nature of training and
the background of the performer. Whether the environment is
open or closed also affects the acquisition of skill. In a closed
environment, the conditions in which the skill is performed are
always essentially the same, whereas in open environments
conditions are changing and uncertain. In an open environ-
ment, the environment itself dictates to some extent how the
skill must be performed. For example, given that ice conditions
are perfect, a figure skater simply performs the learned skills
regardless of where the arena is located. A hockey player, on
the other hand, must be aware of the positions of other players
in order to appropriately exercise learned skills.Phases of Skill AcquisitionIn the beginning of the chapter, Fitts’s (1962/1990, 1964;
Fitts & Posner, 1967) framework was mentioned in the con-
text of the role of memory in skilled performance. Fitts did
not posit any specific mechanisms that describe changes in
the role or importance of memory, attention, or other elemen-
tary processes, but his general framework is consistent with a
shift from attentive, deliberative processing of the environ-
ment and task requirements to a dependence on retrieval from
long-term memory, in one form or another. Fitts describes
three phases of skill acquisition, the cognitive, associativeor
fixation,andautonomousphases. As described above, the
cognitive phase emphasizes the role of declarative memory
and cognitive processes in performance. In the associative, or
fixation, phase, “correct patterns of behavior are fixated by
continued practice” (Fitts, 1962/1990, p. 286). This phase
may last for days or months before the autonomous phase is
reached. At this final phase, performance is relatively free
from errors (although performance time may continue to im-
prove) and shows increasing resistance to stress and interfer-
ence from concurrent activities. Fitts suggests that this stage