Willem B. Verwey

Control of automated behavior: insights from the discrete sequence production task

Work with the discrete sequence production (DSP) task has provided a substantial literature on discrete sequencing skill over the last decades. The purpose of the current article is to provide a comprehensive overview of this literature and of the theoretical progress that it has prompted. We start with a description of the DSP task and the phenomena that are typically observed with it. Then we propose a cognitive model, the dual processor model (DPM), which explains performance of (skilled) discrete key-press sequences. Key features of this model are the distinction between a cognitive processor and a motor system (i.e., motor buffer and motor processor), the interplay between these two processing systems, and the possibility to execute familiar sequences in two different execution modes. We further discuss how this model relates to several related sequence skill research paradigms and models, and we outline outstanding questions for future research throughout the paper. We conclude by sketching a tentative neural implementation of the DPM.

Concatenating familiar movement sequences: the versatile cognitive processor

Earlier studies demonstrated that practicing a series of key presses in a fixed order yields memory representations (i.e., motor chunks) that can be selected and used for sequence execution as if familiar key pressing sequences are single responses. In order to examine whether these motor chunks are robust in different situations and whether preparation for one sequence may overlap with execution of another one, two experiments were carried out in which participants executed two highly practiced keying sequences in rapid succession in response to two simultaneously presented stimuli. The results confirmed robustness of motor chunks, even when the sequences included only two elements, and showed that preparation (and in particular, selection) of a forthcoming sequence may occur during execution of the earlier sequence. Sequences including only two keys appeared to be slowed more by concurrent preparation than longer sequences. Together these results suggest that the execution of familiar keying sequences is predominantly carried out by a dedicated motor processor, and that the cognitive processor can be allocated to preparing a forthcoming sequence (e.g., during execution of an earlier sequence) or, some times, to selecting individual sequence elements in parallel to the motor processor.

Representing Serial Action and Perception

This article presents a review on the representational base of sequence learning in the serial reaction time task. The first part of the article addresses the major questions and challenges that underlie the debate on implicit and explicit learning. In the second part, the informational content that underlies sequence representations is reviewed. The latter issue has produced a rich and equivocal literature. A taxonomy illustrates that substantial support exists for associations between successive stimulus features, between successive response features, and between successive response-to-stimulus compounds. We suggest that sequence learning is not predetermined with respect to one particular type of information but, rather, develops according to an overall principle of activation contingent on task characteristics. Moreover, substantiating such an integrative approach is proposed by a synthesis with the dual-system model (Keele, Ivry, Mayr, Hazeltine, & Heuer, 2003).

On-line driver workload estimation : Effects of road situation and age on secondary task measures

In order to develop a driver-car interface that adapts the presentation of messages generated by in-vehicle information systems to driver workload, two experiments investigated potential determinants of driver visual and mental workload as indicated by performance on two secondary tasks. Experiment 1 suggested that road situation is a major determinant of visual and mental workload of the driver and that the processing resources of older drivers are somewhat more limited than those of younger and middle-aged drivers. Familiarity with the area of driving (when guided) and time of day (associated with traffic density) showed no secondary task effects. Experiment 2 showed that the categorization of road situations, proposed in Experiment 1, could underlie adaptation of visually loading messages to the workload incurred by driving. This was not found with respect to mentally loading messages.

Evidence for a multistage model of practice in a sequential movement task.

This study explored the effects of practice when discrete keypress sequences were produced in response to a stimulus. Eighteen students practiced 3 sequences with consistent stimulus-sequence mappings and 2 sequences with varied mappings in a 2,500-trial practice phase. In 2 subsequent transfer phases, the performance effects were assessed of a preceding serial reaction time task and of reversal of 2 consistently practiced stimulus-sequence mappings. The results are explained by the development of 3 types of memory codes (stimulus?response associations, stimulus?response rules, and motor chunks) that are used at 2 independent stages in a serial information-processing stage architecture

On the role of the SMA in the discrete sequence production task: a TMS study

Participants practiced two discrete six-key sequences for a total of 420 trials. The 1 x 6 sequence had a unique order of key presses while the 2 x 3 sequence involved repetition of a three-key segment. Both sequences showed a long interkey interval halfway the sequence indicating hierarchical sequence control in that not only the 2 x 3 but also the 1 x 6 sequence was executed as two successive motor chunks. Besides, the second part of both sequences was executed faster than the first part. This supports the earlier notion of a motor processor executing the elements of familiar motor chunks and a cognitive processor triggering either these motor chunks or individual sequence elements. Low-frequency, off-line transcranial magnetic stimulation (TMS) of the supplementary motor area (SMA) counteracted normal improvement with practice of key presses at all sequence positions. Together, these results are in line with the notion that with moderate practice, the SMA executes short sequence fragments that are concatenated by other brain structures.

Diminished motor skill development in elderly: indications for limited motor chunk use.

The present study examined whether elderly use motor chunks after practicing discrete keying sequences, just like young adults, or whether they perhaps learn these movement patterns in a different way. To that end, elderly (75-88) and young adults (18-28) practiced as part of the discrete sequence production (DSP) task two fixed series of three and six key presses. The results demonstrate that elderly did improve with practice but this improvement was largely sequence-unspecific. Detailed analyses showed that, in contrast to young adults, most elderly did not use motor chunks, had little explicit sequence knowledge, and remained highly dependent on external stimuli. Still, elderly did show sequence-specific learning with a 6-key sequence that can be explained by an associative learning mechanism.

Evidence for the development of concurrent processing in a sequential keypressing task

This paper describes an experiment that aimed at examining the effects of extended practice in a sequential keypressing task. More specifically, predictions of three execution model were tested. First, the classic subprogram-retrieval model (Sternberg et al., 1978) assumes that an action sequence is programmed entirely before sequence execution while later, during sequence execution, instructions for the individual units in the sequence are retrieved. It predicts that keypressing rate decreases with sequence length but specific effects of practice are not predicted. The second mechanism, concurrent processing, assumes that various forms of information processing become increasingly concurrent in the course of practice. More specifically, it is proposed that with practice motor programming and retrieval of individual motor units from a short-term motor buffer concur with actual keypressing which, however, may delay execution of individual actions. Finally, associative motor unitization asserts that sequence execution comes to rely to an increasing degree on the automatic spread of activation among representations of the individual sequence units so that keypressing rate increases with position in the sequence. These and other predictions were verified with a two-choice sequence production task. One sequence contained four, the other two keypresses. The main results are: (a) a reduction with practice of the difference between the times to initiate long and short sequences, (b) practice had a larger effect on final keypresses than on earlier keypresses, and (c) practice had a larger effect on the final keypress of the long than that of the short sequence. An interesting additional effect was the occurrence of a pronounced `warming-up? effect for all interkey intervals at the second and third day of practice. The results were taken as evidence for the development of concurrent programming and concurrent retrieval while little support was observed for associative motor utinization and subprogram-retrieval.

Effect of sequence length on the execution of familiar keying sequences: Lasting segmentation and preparation?

Abstract The author assessed the mechanisms underlying skilled production of keying sequences in the discrete sequence-production task by examining the effect of sequence length on mean element execution rate (i.e., the rate effect). To that end, participants (N = 9) practiced fixed movement sequences consisting of 2, 4, and 6 key presses for a total of 588 trials per sequence. In the subsequent test phase, the sequences were executed with and without a verbal short-term memory task in both simple and choice reaction time (RT) paradigms. The rate effect was obtained in the discrete sequence-production task—including the typical quadratic increase in sequence execution time (SET, which excludes RT) with sequence length. The rate effect resulted primarily from 6-key sequences that included 1 or 2 relatively slow elements at individually different serial positions. Slowing of the depression of the 2nd response key (R2) in the 2-key sequence reduced the rate effect in the memory task condition, and faster execution of the 1st few elements in each sequence amplified the rate effect in simple RT. Last, the time to respond to random cues increased with position, suggesting that the mechanisms that underlie the rate effect in new sequences and in familiar sequences are different. The data were in line with the notion that coding of longer keying sequences involves motor chunks for the individual sequence segments and information on how those motor chunks are to be concatenated.

Optimizing conditions for computer-assisted anatomical learning

An experiment evaluated the impact of two typical features of virtual learning environments on anatomical learning for users of differing visuo-spatial ability. The two features studied are computer-implemented stereopsis (the spatial information that is based on differences in visual patterns projected in both eyes) and interactivity (the possibility to actively and continuously change ones view of computer-mediated objects). Participants of differing visuo-spatial ability learned about human abdominal organs via anatomical three-dimensional (3D) reconstructions using either a stereoptic study phase (involving stereopsis and interactivity) or using a biocular study phase that involved neither stereopsis nor interactivity. Subsequent tests assessed the acquired knowledge in tasks involving (a) identification of anatomical structures in anatomical 2D cross-sections (i.e. typical Computed Tomography pictures) in an identification task, and (b) localization of these cross-sections in a frontal view of the anatomy in a localization task. The results show that the stereoptic group performed significantly better on both tasks and that participants of low visuo-spatial ability benefited more from the stereoptic study phase than those of high visuo-spatial ability.