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

Abstract

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.

Keywords: automated behavior; motor skill; sequence learning.

Figure 1

A depiction of a typical DSP task including a 4-key sequence: responding (R₁–R₄) to a series of stimuli (S₁–S₄) with RSI = 0 ms.

Figure 2

Executing a 6-key sequence and its typical reaction time pattern. It involves the processing phases initiation, concatenation, and (mere) execution. Please note that with smaller sequence lengths (<5 key-presses) the relatively slow T half way through (concatenation) is not typically observed.

Figure 3

The dual processor model (DPM) involves a cognitive processor (CP) and a motor processor (MP) that together drive three distinct modes of sequence execution, through long-term sequential knowledge and the temporary storage in a motor buffer (in the case of motor chunking). S_n and R_n denote the current stimulus and corresponding response within the sequence, respectively. Black arrows and boxes denote the relevant processing routes. (A) In the reaction mode, responses are selected by the cognitive processor (CP) on the basis of S-R translation. (B) Ongoing response selection by the CP is facilitated by the first, still weak, sequence knowledge that develops. (C) Motor chunks have developed, and the CP selects these motor chunks, loads them in the motor buffer, from where the motor processor can execute them. Please note (I) that panel C also depicts the assumption of DPM that there can be a race between two response processes: the triggering of responses by the motor processor reading response related codes from the motor buffer, and response selection by the cognitive processor on basis of continued S-R translation or explicit sequence knowledge (dark gray arrow with black lining). Also note (II) that a fourth theoretical possibility is not depicted here, namely that the CP can load the motor buffer not by selecting motor chunks, but rather by (the slower process of) selecting and loading individual response elements of a (relatively) unfamiliar sequence.