Types of Skills 507is characterized by a shift from visual to proprioceptive feed-
back. He also points out that many skills can be described in
terms of subskills, and that each of these subroutines may de-
velop at its own rate. This idea provides the basis for part-
task training, discussed below.
Anderson’s (1982, 1983, 1993) account of skill acquisi-
tion also consists of an early declarativephase and a later
proceduralphase, with an intermediary process of knowledge
compilationthat enables the learner to move from the declar-
ative to the procedural phase by converting the declarative
knowledge of the learner into a procedural form. Procedures,
orproductions,are basically if-then rules. On the basis of
productions, even complex environmental conditions (if
compiled) can trigger mental or overt actions without the re-
quirement that all relevant aspects of the situation be kept
active in working memory for the application of general in-
terpretive mechanisms.
Mechanisms of Change
According to Anderson (1982), practice results in increased
speed of processing of component procedures. Procedures
may also be compiled or restructured through processes of
chunking (Newell & Rosenbloom, 1981). Carlson, Sullivan,
and Schneider (1989) investigated the relative contributions
of component speed-up and restructuring for the tasks of pre-
dicting or verifying the output of logic gates (e.g., “if all inputs
are equal to 1, the output is 1; otherwise the output is 0” [and
gate]). They found that prediction judgments were faster than
verification judgments and that both types of judgments were
faster when the gate type evaluated whether certain elements
were present rather than if they were absent. The same relative
ordering of task difficulty was maintained for the full 1,200
trials of practice, suggesting that participants were not able to
automatize the procedures used to make the judgments. In
order to test whether attentional resources were freed up as a
function of practice, a memory load was introduced at two
points during practice. The memory load consisted either of
irrelevant digits (i.e., digits other than 0 or 1), digits that had to
be substituted into the comparisons in order to make the judg-
ments, or digits that could, in principle, be used in logic gate
problems, but that were not needed to actually solve the prob-
lems. The memory load had an effect on logic gate perfor-
mance only when it had to be accessed in order to solve the
problem, and this effect was the same both early and late in
practice. Thus, Carlson et al. did not find evidence for qualita-
tive changes in how the task was performed.
When the task is more complex, requiring the formation of
subgoals, evidence for restructuring and speed-up of compo-
nent processes is sometimes found. Carlson, Khoo, Yaure,
and Schneider (1990) devised a task in which complex cir-
cuits of logic gates had to be tested. They found that both the
number of moves required to troubleshoot a circuit (an indi-
cation of the efficiency of the search strategy) and the time
per move (the efficiency of operator application) decreased
as a function of practice, with especially big improvements
early in practice. The pattern of moves also changed with
practice, indicating that learners did form subgoals and came
to recognize the conditions under which these subgoals could
be applied. Retention tests given after 6 months showed re-
tention of both improvements in the speed of component pro-
cessing and in the restructuring of the component steps.TYPES OF SKILLSIn order to gain more insight into the nature of learning and
the conditions that promote the acquisition of skills, it is nec-
essary to consider performance in a wide range of tasks. Most
real-world skills include perceptual, cognitive, and motor
components. Although the goal of skills researchers is to un-
derstand complex behavior, much can be learned by attempt-
ing to isolate these basic information processes and to look at
the development of perceptual, cognitive, and motor compo-
nents of skill.Perceptual SkillPerceptual skills are those skills that depend heavily on the
ability to discriminate between and to classify stimuli on the
basis of perceivable attributes of the stimuli. In some skills,
such as wine tasting (Melcher & Schooler, 1996) or deter-
mining the sex of baby chicks (Lunn, 1948), the skill to be
learned is clearly primarily perceptual. However, often
perceptual skills are an important part of other skills. For ex-
ample, copying high-speed Morse code depends on the per-
ceptual ability to parse the dits and dahs that make up the
message and to group these symbols into conceptual units,
the motor ability to quickly type the message, and the strate-
gic ability to copy behind,that is, to allow the typing of the
message to lag behind the decoding of the message (Wisher,
Sabol, & Kern, 1995). Sports performed in open environ-
ments also depend on perceptual skill. For example, it has
been shown that skill in volleyball is associated with espe-
cially rapid visual search when a volleyball is the target
(Allard & Starkes, 1980).
In order for perceptual skill to develop, features that are
specific to a particular stimulus and that distinguish it from
other stimuli must be learned. One factor that can influence
the development of perceptual skill is labeling. Labeling