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 &

Summary.What is the nature of the human timing mechanism for perceptual judgements about short temporal intervals? One possibility is that initial periodic events, such as tones, establish internal beats which continue after the external events and serve as reference points for the perception of subsequent events. A second possibility is that the timer records the intervals produced by events. Later, the stored intervals can be reproduced or compared to other intervals. A study by Schulze (1978) provided evidence favoring beat-based timing. In contrast, our two experiments support an interval theory. The judgements of intervals between tones is not improved when the events are synchronized with internal beats established by the initial intervals. The conflict between the two sets of results may be resolved by the fact that an interval timer can recycle from one interval to the next, thus operating in a beatlike mode. However, a timer of this sort is just as accurate when comparing intervals that are off the beat.A great deal of research has been concerned with the perception of time. Although "time" is a term in common, many of the problems addressed in different studies are quite different. Much of the work has been concerned with subjective time -that is, judgements of how much time has transpired. Typically those judgements concern seconds, minutes, and even hours. In contrast, little work has been concerned with relatively short intervals measured in terms of a few hundred ms. Such short intervals are characteristic of the timing of a rapid series of movements, as in playing a musical instrument or in speaking, and are also characteristic of the perceptual experiences emanating from rapid production of this sort, such as the music or the speech sounds.The present study is concerned with possible mechanisms that underlie the perception and production of such short intervals as may be relevant to skill. In particular, the study compares two general mechanisms whereby humans distinguish slight irregularities in the timing of otherwise periodic events. The events occur at short intervals, in this case one about every 300 ms. The two mechanisms were described by Schulze (1978). One mechanism, a beat-based timer, essentially involves the synchrony of events. The second type of mechanism, an interval timer, involves Offprint requests to: S. W. Keele comparing the intervals between events. The general idea of a beat-based timer is that an initial series of periodic events establishes an internal beat that persists after the initial events. Whether or not subsequent events are perceived as occurring at the proper time will depend on the degree to which they are synchronized with the internal beat. In contrast, an interval timer registers the duration of an interval between events, and that temporal memory is then compared to other intervals in order to judge whether or not they are the same.Schulze (1978) devised a test between the theories using a paradigm which we repeat here. On each trial he presented a series of...

. In Metelli (1974)made an important contribution by identifying order and magnitude restrictions for a pattern of intensities and showing that when they are satisfied the perception of transparency readily occurs. These restrictions were derived from a physical model of transparency. We argue that the visual system does not use intensity information to compute indices of transmittance and reflectance analogous to what an optical engineer might do in describing a physical instance of transparency. Rather, a lightness pattern affects perceptual transparency, just as geometric properties do, through processes that impose an organization on sensory information rather than through processes that recover quantitative descriptions. In the absence of depth cues, such as stereopsis and motion parallax, the perception of transparency occurs when the lightness relations in a pattern favor the perception of a continuous boundary across x-junctions. We present evidence for two kinds of violations of the order and magnitude restrictions: simple and strong. Transparency judgments, although reduced in number, still occur for simple violations of the order and the magnitude restrictions. Transparency judgments occur relatively infrequently for strong violations. A physical model of transparency fails to capture the difference between simple and strong violations of the order and magnitude restrictions. We discuss (1) the basis for differentiating between simple and strong violations of the order and magnitude restrictions, (2) the effect simple and strong violations have on the perception of transparency, and (3)the occurrence of transparency with and without color constancy (i.e., the color seen through the transparent surface looks or fails to look the same as the color seen directly).where a is the proportion of light reflected from surface A (corresponding to the areal fraction occupied by the open sector of the episcotister), I-a is the proportion of light reflected from the blades of the episcotister (corresponding to the areal fraction occupied by the blades of the episcotister), a is the reflectance of surface A, b is the reflectance of surface B, and e is the reflectance of the episcotister blades. Solving Equations 1 and 2 for a and e yields Metelli (1974) proposed a model for the perception of transparency based on a physical model of transparency. Beck, Prazdny, and Ivry (1984) reported findings that challenge the adequacy of the Metelli model. The implications of these findings were not made fully clear in the earlier paper; thus, in this paper, we present the Metelli model, the difficulties we see with the Metelli model, an alternative model based on processes of figural organization, and an experiment that further clarifies the conditions for the perception of transparency.This research was supported by National Science Foundation Grant INT-8418187 andby Air Force of Scientific Research Grant AFOSR-85-0359. Requests for reprints should be sent to Iacob Beck, Department of Psychology, University of Oregon, Eugene,...

Previous work (Keele & Hawkins, 1982; Keele, Pokorny, Corcos, & Ivry, 1985) has suggested two general factors of coordination that differentiate people across a variety of motor movements, factors of timing and maximum rate of successive movements. This study provides comparable evidence for a third general factor of coordination, that of force control. Subjects who exhibit low variability in reproducing a target force with one effector, the finger, tend to show low variability with two other effectors, the foot and forearm. In addition, ability in force control cuts across different force ranges and across situations where force control is either the primary goal or the secondary goal. Force records obtained during a periodic tapping task show that, although force control is largely independent of timing, there are some interactions between the two factors. Force variation appears to distort timing a small amount in part because larger forces speed up implementation of movement, thereby shortening preceding intervals and lengthening following ones, and in part because force variation alters central-timing mechanisms.

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