Types of Skills 509Walker, Czerwinski, and Feldman (1997) review evidence
from choice-reaction tasks and visual search studies that cast
doubt on the idea that, at a fundamental level, performance
becomes automatic as a function of practice. For example, it
has been shown that one of the variables that most directly
affects response selection, stimulus-response compatibility,
continues to affect performance even after much practice and
after performance seems to have reached an asymptotic level
(Dutta & Proctor, 1992; Fitts & Seeger, 1953; see the chapter
by Proctor & Vu).
Motor Skill
Motor skills have been extensively studied since the very
beginnings of experimental psychology (e.g., Woodworth,
1899; Bryan & Harter, 1897, 1899). Whether one empha-
sizes “the integration of well-adjusted muscular perfor-
mance” (Pear, 1948, p. 92) or “continuous interaction of
response processes with input and feedback processes” (Fitts,
1962/1990, p. 275), motor performance often plays a central
role in definitions of skill. There are three problems to be
solved in learning to perform a motor task with skill. The
degrees-of-freedomproblem arises because there are many
ways of performing any given action, and the performer is
faced with the task of finding the best one. The serial-order
problem concerns the timing and ordering of sequences of
movements. Finally, the perceptual-motor integrationprob-
lem involves coordinating the interactions between the per-
ceptual and motor systems.
The Degrees-of-Freedom Problem
Degrees of freedom are, to put it simply, the dimensions of
movement permitted by the joints involved in performing an
action. In general, the more complex the movement, the more
degrees of freedom there are available (see the chapter by
Heuer). A goal of skilled performance is to make optimal use
of the available degrees of freedom. Bernstein (1967) sug-
gested that, early in performance, the degrees-of-freedom
problem may be solved by simply fixing or “freezing” some
of the joints involved in the action. Vereijken, van Emmerik,
Whiting, and Newell (1992) showed that as a person masters
a skill (in this case, learing to ski on a ski simulator), the de-
grees of freedom that are initially fixed are gradually freed
such that the use of these joints can also enter into perfor-
mance. As yet, little research has been done on whether fixing
degrees of freedom is a general strategy, and results from the
studies that have been done are mixed. Broderick and Newell
(1999) suggest that both the task and the skill level of the
performer must be considered, because the coordination
patterns observed seem to depend on an interaction of the
task and performer. In some cases, novices seem rigid and
stiff (Vereijken et al., 1992). In other cases, novices show
much more variability than experts (Broderick & Newell,
1999). Coordination of multiple effectors is more compli-
cated than just a restriction of the range of movement of
specific joints.The Serial-Order ProblemOriginal ideas about the serial-order problem focused on the
relation between one response and the next. In the linear-chain
hypothesis of Lashley (1951), the sensory feedback produced
by a response initiates the next response in the sequence. Such
a process may explain learning when the two responses in-
volved have a unique association such that the second re-
sponse always follows the first. In such a case, learning might
occur automatically, as discussed for unambiguous sequences
in the earlier section on sequence learning. However, such a
hypothesis cannot explain the learning of ambiguous se-
quences. Lashley hypothesized that control can also be hierar-
chical, and this hypothesis is supported by studies that show
that the pauses that performers make when carrying out a se-
quence of finger movements correspond to the hierarchical
structure of the sequence (Povel & Collard, 1982).The Perceptual-Motor Integration ProblemThe perceptual-motor integration problem involves the ways
perception influences action and action influences percep-
tion. Perception provides visual information, as well as sen-
sory input from receptors in the muscles, joints, tendons, and
skin. Of these information sources, the role of vision in learn-
ing has received the most study. Despite rather extensive re-
search, however, it is difficult to make generalizations about
the role of vision in skilled performance. In many cases, if
vision does play an important role in performance, it contin-
ues to play an important role even after extensive practice.
For example, Khan and Franks (2000) showed that a group
allowed to view the cursor while performing a cursor posi-
tioning task (in which a cursor had to be moved onto a target)
performed better than a group that saw the cursor only at
the beginning of a trial. When transferred to a no-vision
condition, however, the group that practiced with visual feed-
back performed much worse than the group that had prac-
ticed without such feedback.
Some studies have suggested that visual feedback some-
times becomes moreimportant with practice (Proteau &
Cournoyer, 1990). Such findings are predicted by the
specificity-of-practice hypothesis(Proteau, 1992; Proteau,
Marteniuk, & Levesque, 1992), according to which different