Previous work has shown that Ss can learn to classify sets of patterns which are distortions of a prototype, even when they have not seen the prototype. In this paper it is shown that after learning a set of patterns, the prototype (schema) of that set is more easily classified than control patterns which are also within the learned category. As the variability among the memorized patterns increases, so does the ability of Ss to classify highly distorted new instances. These findings argue that information about the schema is abstracted from the stored instances with very high efficiency. It is unclear whether the abstraction of information involved in classifying the schema occurs while learning the original patterns or whether the abstraction process takes place at the time of the first presentation of the schema.

Flexible control of action requires the ability to disengage from previous goals or task sets. The authors tested the hypothesis that disengagement during intentional shifts between task sets is accompanied by inhibition of the previous task set ("backward inhibition"). As an expression of backward inhibition the authors predicted increased response times when shifting to a task set that had to be abandoned recently and, thus, suffers residual inhibition. The critical backward inhibition effect on the level of abstractly defined perceptual task sets was obtained across 6 different experiments. In addition, it was shown that backward inhibition can be differentiated from negative priming (Experiment 2), that it is tied to top-down sequential control (Experiment 3), that it can account at least partially for "residual shift costs" in set-shifting experiments (Experiment 4), and that it occurs even in the context of preplanned sequences of task sets (Experiment 5). Our natural environment is relatively unconstrained with respect to the number of possible actions that could be pursued at any given moment. For example, in many work settings a multitude of different tasks need to be performed. Overall success depends to a large degree on the ability to finish off one task while resisting the tendency to jump to another one for no other reason than its presence in the "field of view." Thus, the ambiguity of external context with respect to action selection needs to be countered by strong and stable internal representations that are often referred to as "task sets" and that constrain the space of possible actions (e.g., Rogers & Monsell, 1995). The importance of such internal representations for normal behavior is clearly apparent in those cases where they seem to be missing. For example, some patients with frontal-lobe damage may show actions (e.g., tooth-brushing) that are triggered by related objects (e.g., a toothbrush) irrespective of current goals (e.g,, Lhermitte, 1983). Goal-related representations that are stable enough to direct behavior even in the face of opposing action tendencies certainly are one of the hallmarks of primate, and in particular of human, thinking and action. They also clearly belong to one of the least understood aspects of higher cognition (e.g., Monsell, 1996).

In this study we investigated the role of attention, sequence structure, and effector specificity in learning a structured sequence of actions. Experiment 1 demonstrated that simple structured sequences can be learned in the presence of attentional distraction. The learning is unaffected by variation in distractor task difficulty, and subjects appear unaware of the structure. The structured sequence knowledge transfers from finger production to arm production {Experiment 2), suggesting that sequence specification resides in an effector-independent system. Experiments 3 and 4 demonstrated that only structures with at least some unique associations (e.g., any association in Structure 15243... or 4 to 3 in Structure 143132...) can be learned under attentional distraction. Structures with all items repeated in different orders in different parts of the structure (e.g., Sequence 132312...) require attention for learning. Such structures may require hierarchic representation, the construction of which takes attention. One of the remarkable capabilities of humans is their ability to learn a variety of novel tasks involving complex motor sequences. They learn to play the violin, knit, serve tennis balls, and perform a variety of language tasks such as speaking, typing, writing, or producing sign. This study addresses three features that might be involved in such learning: attention, structure of the sequence, and effector specificity. These three features will be discussed in succession. Attention and Sequence Learning A large variety of evidence indicates that attention is important in verbal learning. For example, the classic study by Peterson and Peterson (1959) showed that a numeric distractor produced a dramatic loss of recall of short letter strings. Similarly, Fisk and Schneider (1984) found judgment of frequency of previously presented words to drop to chance level when the words were presented concurrently with a numeric distractor. The learning was prevented even though the secondary numeric task was very different from the frequency judgment task. On the basis of these findings, Fisk and Schneider argued that general attentional resources are necessary for modifications of long-term memory. Does the learning of motor sequences also require attention? This question is especially relevant in light of the hypothesis that sequential learning can involve a different memory system, sometimes called procedural memory, than verbal learning or other declarative memory systems (cf. Mishkin &

This study investigated the effects of different types of neurological deficits on timing functions. The performance of Parkinson, cerebellar, cortical, and peripheral neuropathy patients was compared to age-matched control subjects on two separate measures of timing functions. The first task involved the production of timed intervals in which the subjects attempted to maintain a simple rhythm. The second task measured the subjects' perceptual ability to discriminate between small differences in the duration of two intervals. The primacy of the cerebellum in timing functions was demonstrated by the finding that these were the only patients who showed a deficit in both the production and perception of timing tasks. The cerebellar group was found to have increased variability in performing rhythmic tapping and they were less accurate than the other groups in making perceptual discriminations regarding small differences in duration. Critically, this perceptual deficit appears to be specific to the perception of time since the cerebellar patients were unaffected in a control task measuring the perception of loudness. It is argued that the operation of a timing mechanism can be conceptualized as an isolable component of the motor control system. Furthermore, the results suggest that the domain of the cerebellar timing process is not limited to the motor system, but is employed by other perceptual and cognitive systems when temporally predictive computations are needed.