504 Procedural Memory and Skill Acquisition
independently of mental load, but only on events that are ac-
tive in working memory.
The Nature of Implicit Learning
If we accept that learning without intention (and perhaps
without awareness) can occur, we can also ask what the na-
ture of the learning is. For example, is one learning relations
between stimuli, relations between stimulus-response associ-
ations, or the motor sequence? One interesting hypothesis,
similar to the idea that prediction is the basis for condi-
tioned learning, is that it is the response-effect relationship
that is first implicitly learned and that this might provide the
basis for the development of explicit knowledge. To test this
hypothesis, Ziessler (1998) modified Nissen and Bullemer’s
(1987) SRT paradigm so that the location of the stimulus on
a particular trial was determined by the response made on the
previous trial. Rather than responding to the location of the
stimulus, as in Nissen and Bullemer’s task, participants in
Ziessler’s experiments responded to the identity of a target in
the presence of distractors. The location of the target was thus
not relevant for the response, but knowledge of the location
could be used to speed up search and, accordingly, reaction
times.
By varying the predictability of the position of the follow-
ing stimulus (achieved by varying whether all stimuli as-
signed to a certain key predicted the same position), Ziessler
(1998) showed that performance improved more when the
response made reliably predicted the position of the next
stimulus than when it was only sometimes a valid predictor.
Moreover, only the perfectly reliable response-stimulus asso-
ciations condition showed negative transfer to a condition in
which target position was random, as well as showing the
largest increase in reaction time when stimulus-response re-
lations were altered. None of the participants in Ziessler’s
study reported noticing anything predictable in target posi-
tion. Thus, it seems that knowledge of target position was
only implicitly learned.
In the original Nissen and Bullemer (1987) experiments,
responses were made to the location of the stimulus.
Therefore, it is impossible to say whether performance im-
provements depended on the learning of perceptual relations
(the relation of one stimulus to the next), stimulus-response
associations, or response relations (the relation of one re-
sponse to the next). Willingham et al. (1989) attempted to look
separately at the learning of these relations using the SRT task
described above in which the locations of the stimuli follow a
predictable sequence, but requiring that responses be made to
the color of the stimuli, rather than their locations. By assess-
ing performance during practice and in a transfer task in which
locations were responded to, they concluded that sequences in
the stimulus locations were not learned when responses were
based on the color of the stimuli. On the other hand, if practice
was with a task with a predictable sequence of stimulus-
response pairs, considerable learning occurred, as indexed by
better performance than when the stimuli were randomly pre-
sented. However, this group also showed no benefit of practice
in a transfer condition in which responses were made to loca-
tion, even though the responses were exactly the same as in the
practice task, suggesting that the locus of learning was in the
stimulus-response associations. A. Cohen et al. (1990) pre-
sented evidence that suggests that the actual motor responses
made are not critical to sequence learning: After participants
practiced an SRT task using the index, middle, and ring fin-
gers, transfer was virtually perfect in a condition in which only
one finger was used to make responses.
The actual responses made may, however, be a locus of
learning in some types of tasks. Palmer and Meyer (2000) re-
cently tested the separate contributions that conceptual and
motor skill make to the skill of piano playing and found that
the relative importance of the effectors used and the move-
ments made changes as a function of skill level. For low- and
moderately skilled piano players, transfer was greatest when
the motor movements were the same (even though a different
part of the keyboard was used) for pieces played in practice
and transfer. Skilled players, in contrast, showed the most
transfer when conceptual (melody) aspects of the transfer
piece corresponded to the practice piece, even when different
fingers and hands were used. This suggests that the mental
plans for performing an action only become independent of
the required movements at an advanced stage of practice.
Findings that show independence of learning from the effec-
tors used (e.g., A. Cohen et al., 1990) may be limited to rela-
tively simple motor tasks.
It can be concluded that the research on sequence learning
provides evidence that learning can occur without awareness,
although attending to the relevant stimulus aspects does seem
to be required for this learning to occur. The nature of the
learning seems to depend primarily on associations between
stimuli and responses (or between responses and stimuli),
unless the visual demands are made more complex, in which
case perceptual learning also plays a role (see Lewicki,
Czyzewska, & Hoffman, 1987; Stadler, 1989).PROCEDURAL MEMORYSkill acquisition has been described as a transition from re-
liance on verbal, declarative knowledge to a reliance on
procedures or routines for performing tasks. The distinction