Elian de Kleine

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.

Motor skill learning in the middle-aged: limited development of motor chunks and explicit sequence knowledge

The present study examined whether middle-aged participants, like young adults, learn movement patterns by preparing and executing integrated sequence representations (i.e., motor chunks) that eliminate the need for external guidance of individual movements. Twenty-four middle-aged participants (aged 55–62) practiced two fixed key press sequences, one including three and one including six key presses in the discrete sequence production task. Their performance was compared with that of 24 young adults (aged 18–28). In the middle-aged participants motor chunks as well as explicit sequence knowledge appeared to be less developed than in the young adults. This held especially with respect to the unstructured 6-key sequences in which most middle-aged did not develop independence of the key-specific stimuli and learning seems to have been based on associative learning. These results are in line with the notion that sequence learning involves several mechanisms and that aging affects the relative contribution of these mechanisms.

Cognitive processing in new and practiced discrete keying sequences.

This study addresses the role of cognitive control in the initiation and execution of familiar and unfamiliar movement sequences. To become familiar with two movement sequences participants first practiced two discrete key press sequences by responding to two fixed series of 6-key specific stimuli. In the ensuing test phase they executed these two familiar and also two unfamiliar keying sequences while there was a two-third chance a tone was presented together with one randomly selected key specific stimulus in each sequence. In the counting condition of the test phase participants counted the low pitched (i.e., target) tones. By and large the results support the dual processor model in which the prime role of the cognitive processor shifts from executing to initiating sequences while the gradual development of motor chunks allows a motor processor to execute the sequences. Yet, the results extend this simple model by suggesting that with little practice sequence execution is based also on some non-cognitive (perhaps associative) learning mechanism and, for some participants, on the use of explicit sequence knowledge. Also, after extensive practice the cognitive processor appears to still contribute to slower responses. The occurrence of long interkey intervals was replicated suggesting that fixed 6-key sequences include several motor chunks. Yet, no indication was found that the cognitive processor is responsible for concatenating these chunks.

Representations underlying skill in the discrete sequence production task: effect of hand used and hand position

Various studies suggest that movement sequences are initially learned predominantly in effector-independent spatial coordinates and only after extended practice in effector-dependent coordinates. The present study examined this notion for the discrete sequence production (DSP) task by manipulating the hand used and the position of the hand relative to the body. During sequence learning in Experiment 1, in which sequences were executed by reacting to key-specific cues, hand position appeared important for execution with the practiced but not with the unpracticed hand. In Experiment 2 entire sequences were executed by reacting to one cue. This produced similar results as in Experiment 1. These experiments support the notion that robustness of sequencing skill is based on several codes, one being a representation that is both effector and position dependent.

Motor learning and chunking in dyslexia.

The authors investigated whether participants with dyslexia had problems with executing discrete keying sequences and with switching between chunks in those sequences. Participants with dyslexia and participants in the control group executed 2 6-key sequences each, with 1 sequence consisting of 2 successive instances of 1 3-key segment (2 x 3 sequence) and the other not involving such a repetition (1 x 6 sequence). The authors assumed that during execution of the 2 x 3 sequence, the same chunk could be reused, whereas during execution of the 1 x 6 sequence a switch between chunks had to be made. Participants with dyslexia were slower than participants in the control group in executing the 1 x 6 sequence, but not the 2 x 3 sequence. The authors suggest that the smaller amount of repetitions of the chunks in the 1 x 6 sequence or the increased difficulty of the 1 x 6 sequence led to the slowed execution of the 1 x 6 sequence in participants with dyslexia.

Context-dependent motor skill and the role of practice.

Research has shown that retrieval of learned information is better when the original learning context is reinstated during testing than when this context is changed. Recently, such contextual dependencies have also been found for perceptual-motor behavior. The current study investigated the nature of context-dependent learning in the discrete sequence production task, and in addition examined whether the amount of practice affects the extent to which sequences are sensitive to contextual alterations. It was found that changing contextual cues—but not the removal of such cues—had a detrimental effect on performance. Moreover, this effect was observed only after limited practice, but not after extensive practice. Our findings support the notion of a novel type of context-dependent learning during initial motor skill acquisition and demonstrate that this context-dependence reduces with practice. It is proposed that a gradual development with practice from stimulus-driven to representation-driven sequence execution underlies this practice effect.

Decreased load on general motor preparation and visual-working memory while preparing familiar as compared to unfamiliar movement sequences

Learning movement sequences is thought to develop from an initial controlled attentive phase to a more automatic inattentive phase. Furthermore, execution of sequences becomes faster with practice, which may result from changes at a general motor processing level rather than at an effector specific motor processing level. In the current study, we examined whether these changes are already present during preparation. Fixed series of six keypresses, either familiar or unfamiliar, had to be prepared and executed/withheld after a go/nogo signal. Reaction time results confirmed that familiar sequences were executed faster than unfamiliar sequences. Results derived from the electroencephalogram showed a decreased demand on general motor preparation and visual-working memory before familiar sequences as compared to unfamiliar sequences. We propose that with familiar sequences the presetting segments of responses is less demanding than with unfamiliar sequences, as familiar sequences can be regarded as less complex than unfamiliar sequences. Finally, the decreasing demand on visual-working memory before familiar sequences suggests that sequence learning indeed develops from an attentive to an automatic phase.Learning movement sequences is thought to develop from an initial controlled attentive phase to a more automatic inattentive phase. Furthermore, execution of sequences becomes faster with practice, which may result from changes at a general motor processing level rather than at an effector specific motor processing level. In the current study, we examined whether these changes are already present during preparation. Fixed series of six keypresses, either familiar or unfamiliar, had to be prepared and executed/withheld after a go/nogo signal. Reaction time results confirmed that familiar sequences were executed faster than unfamiliar sequences. Results derived from the electroencephalogram showed a decreased demand on general motor preparation and visual-working memory before familiar sequences as compared to unfamiliar sequences. We propose that with familiar sequences the presetting segments of responses is less demanding than with unfamiliar sequences, as familiar sequences can be regarded as less complex than unfamiliar sequences. Finally, the decreasing demand on visual-working memory before familiar sequences suggests that sequence learning indeed develops from an attentive to an automatic phase.

Context-dependent motor skill: perceptual processing in memory-based sequence production

Previous studies have shown that motor sequencing skill can benefit from the reinstatement of the learning context—even with respect to features that are formally not required for appropriate task performance. The present study explored whether such context-dependence develops when sequence execution is fully memory-based—and thus no longer assisted by stimulus–response translations. Specifically, we aimed to distinguish between preparation and execution processes. Participants performed two keying sequences in a go/no-go version of the discrete sequence production task in which the context consisted of the color in which the target keys of a particular sequence were displayed. In a subsequent test phase, these colors either were the same as during practice, were reversed for the two sequences or were novel. Results showed that, irrespective of the amount of practice, performance across all key presses in the reversed context condition was impaired relative to performance in the same and novel contexts. This suggests that the online preparation and/or execution of single key presses of the sequence is context-dependent. We propose that a cognitive processor is responsible both for these online processes and for advance sequence preparation and that combined findings from the current and previous studies build toward the notion that the cognitive processor is highly sensitive to changes in context across the various roles that it performs.

The premotor theory of attention as an account for the Simon effect

The Simon effect refers to the phenomenon that responses are faster when the irrelevant location of a stimulus corresponds with the response location than when these locations do not correspond. In the current paper we examined the viability of an updated version of the premotor theory of attention (PMTA) as an account for the Simon effect. Two predictions were evaluated. First, in the case of focused attention at the relevant target position a strong reduction of the Simon effect should be observed as the Simon effect according to PMTA crucially depends on attentional orienting. Secondly, if attention is directed towards a location then this orienting by itself should already be sufficient for producing a Simon effect, as stimulus presence is not required. Our data confirmed these predictions thereby supporting the relevance of the PMTA for the Simon effect.

Post-error slowing in sequential action: an aging study

Previous studies demonstrated significant differences in the learning and performance of discrete movement sequences across the lifespan: Young adults (18–28 years) showed more indications for the development of (implicit) motor chunks and explicit sequence knowledge than middle-aged (55–62 years; Verwey et al., 2011) and elderly participants (75–88 years; Verwey, 2010). Still, even in the absence of indications for motor chunks, the middle-aged and elderly participants showed some performance improvement too. This was attributed to a sequence learning mechanism in which individual reactions are primed by implicit sequential knowledge. The present work further examined sequential movement skill across these age groups. We explored the consequences of making an error on the execution of a subsequent sequence, and investigated whether this is modulated by aging. To that end, we re-analyzed the data from our previous studies. Results demonstrate that sequencing performance is slowed after an error has been made in the previous sequence. Importantly, for young adults and middle-aged participants the observed slowing was also accompanied by increased accuracy after an error. We suggest that slowing in these age groups involves both functional and non-functional components, while slowing in elderly participants is non-functional. Moreover, using action sequences (instead of single key-presses) may allow to better track the effects on performance of making an error.