Procedural Memory 505between performance based on explicit versus procedural
knowledge has led to the conception of different ways of
learning and knowing, sometimes described as knowing that
versusknowing how. Explicit memory requires the conscious
directing of attention to the act of recall for remembering
facts (i.e., knowledge that), whereas the performance of a
skilled action (i.e., knowledge how), although it also reflects
past experience, does not involve active attention or con-
scious recall (Squire & Cohen, 1984). Much research indi-
cates that procedural learning,indexed by improvements in
the execution of task elements, may involve a different sys-
tem from the declarative learning of facts and instructions.
Indeed, it appears that there are different memory systems
underlying declarative and procedural learning.
Tulving (1985) describedprocedural memoryas a memory
system that “enables organisms to retain learned connections
between stimuli and responses, including those involving
complex stimulus patterns and response chains, and to re-
spond adaptively to the environment” (p. 387). In Tulving’s
view, procedural memory differs from episodic and semantic
memory in the nature of acquiring, representing, and express-
ing knowledge, as well as in the kind of conscious awareness
that characterizes it. Procedural knowledge is available only
in the form of overt expression and is not available for con-
scious introspection. Tulving describes procedural learning as
“tuning” (Rumelhart & Norman, 1978), in the sense that pro-
cedural memory provides prescriptive knowledge that can be
used to guide future action without containing specific infor-
mation about the past. In this view, procedural learning is ab-
stract in the sense that there is no memory of specific prior
events, but it reflects the acquisition, retention, and retrieval
of knowledge expressed through experience-induced changes
in performance.
Evidence for Procedural Memory
One of the most convincing sources of evidence for a distinc-
tion between declarative and procedural memory comes from
demonstrations of benefits of practice or learning in amnesic
individuals. The observation that amnesic persons sometimes
do show good memory performance across long retention
intervals was made by Claperède (1911), who remarked that
one of his patients’ behavior was altered by experience and
that this altered behavior outlasted the patient’s memory of
the experience itself. His patient, a woman with Korsakoff’s
syndrome, learned not to shake hands with the doctor after he
had pricked her with a pin secreted in his hand, but she was
unable to tell the doctor why she declined to do so. Such
patients can sometimes acquire information at a normal rate
and can maintain normal performance across delays. In the
absence of the ability to recognize having previously seen a
particular stimulus, task, or, in some cases, even the experi-
menter, many amnesic persons have demonstrated the ability
to acquire and retain perceptual-motor skills, such as rotory
pursuit and mirror drawing, cognitive skills (e.g., solving jig-
saw puzzles or the tower of Hanoi, or using a mathematical
rule), and perceptual skill, such as reading mirror-reversed
text (N. J. Cohen, 1984) or learning mazes (Corkin, 1965).
For example, Nissen and Bullemer’s (1987) study, described
above, showed that amnesic individuals evidence just as
much improvement in the SRT task as do normally function-
ing individuals (see Figure 18.2).
Brooks and Baddeley (1976) showed that both Korsakoff
patients and postencephalitic patients improved in the rotary-
pursuit task. Performance of amnesic individuals is often
equivalent to that of normal controls in a variety of perceptual-
motor tasks; however, they do not benefit as much as normal
controls from the repetition of specific items. Although
amnesic persons can show preserved memory for particular
stimuli, as evidenced by facilitation of certain aspects of test
performance based on prior exposure to stimulus materials
(i.e.,priming;e.g., Jacoby & Witherspoon, 1982; Verfaellie,
Bauer, & Bowers, 1991), their recognition memory for the
stimuli is poor. Thus, amnesic individuals seem to possess
normal pattern-analyzing operations or encoding procedures
but poor declarative memory for item-specific information
that would normally be acquired from applying these opera-
tions or procedures.A Procedural Memory System?According to Tulving (1985), a memory system consists of
memory processes and a supportive structure for those
processes. Two important structures for procedural learning
seem to be the basal ganglia and the cerebellum. At the mo-
ment, there are several different hypotheses about the roles of
these two structures. One hypothesis is that learning repeti-
tive motor sequences depends on the basal ganglia, whereas
learning new mappings of visual cues to motor responses
depends on the cerebellum (Willingham, Koroshetz, &
Peterson, 1996). Another hypothesis is that the cerebellum is
needed for closed-loop skill learning, in which visual feed-
back about errors in movement is available and must be used,
whereas open-loop skill learning, in which movements are
executed without feedback, depends more on the basal gan-
glia (Gabrieli, 1998). Hikosaka et al. (1999) stress the cere-
bellum’s role in the timing of movements and suggest that the
basal ganglia is involved in reward-based evaluation.
Flament and Ebner (1996) propose that the role of the
cerebellum as a comparator of desired motor output and