Mechanisms for the generation and regulation of sequential behaviour

A critical aspect of much human behaviour is the generation and regulation of sequential activities. Such behaviour is seen in both naturalistic settings such as routine action and language production and laboratory tasks such as serial recall and many reaction time experiments. There are a variety of computational mechanisms that may support the generation and regulation of sequential behaviours, ranging from those underlying Turing machines to those employed by recurrent connectionist networks. This paper surveys a range of such mechanisms, together with a range of empirical phenomena related to human sequential behaviour. It is argued that the empirical phenomena pose difficulties for most sequencing mechanisms, but that converging evidence from behavioural flexibility, error data arising from when the system is stressed or when it is damaged following brain injury, and between-trial effects in reaction time tasks, point to a hybrid symbolic activation-based mechanism for the generation and regulation of sequential behaviour. Some implications of this view for the nature of mental computation are highlighted

Order and disorder in everyday action: the roles of contention scheduling and supervisory attention

This paper describes the contention scheduling/supervisory attentional system approach to action selection and uses this account to structure a survey of current theories of the control of action. The focus is on how such theories account for the types of error produced by some patients with frontal and/or left temporoparietal damage when attempting everyday tasks. Four issues, concerning both the theories and their accounts of everyday action breakdown, emerge: first, whether multiple control systems, each capable of controlling action in different situations, exist; second, whether different forms of damage at the neural level result in conceptually distinct disorders; third, whether semantic/conceptual knowledge of objects and actions can be dissociated from control mechanisms, and if so what computational principles govern sequential control; and fourth, whether disorders of everyday action should be attributed to a loss of semantic/conceptual knowledge, a malfunction of control, or some combination of the two

Tool use and related errors in ideational apraxia: The quantitative simulation of patient error profiles

The behaviour of ideational apraxic patients on simple tasks involving multiple objects is typically marked by a variety of errors. While some of these errors concern the sequential organisation of action through time, many relate to the misuse of, or failure to use, necessary or appropriate tools. In this paper we apply the computational model of Cooper & Shallice (2000) to five standard multiple object tasks used in clinical assessment and demonstrate how, when lesioned, the model can account for the error profiles of two ideational apraxic patients discussed by Rumiati et al. (2001). Application of the model to the multiple object tasks demonstrates the generality of the model, while the account of the error profiles extends previous work (Cooper et al., 2005) in which ideational apraxia was argued to arise from a generalised disturbance of object representations that are held to trigger action schemas

Cognitive control in the generation of random sequences: a computational study of secondary task effects

Cognitive control processes, such as those involved in response inhibition or task switching, have been the focus of much recent research. Few studies, however, have considered how such processes work together in tasks that require multiple control processes. This paper reports a computational study of random sequence generation and the cognitive control processes involved therein. The task, which is argued to involve multiple control processes, produces several dependent measures. These measures are held to be differentially dependent on the differential efficacy of the various underlying control processes. Initial simulations demonstrate that the model is capable of reproducing subject performance on the basic task. Additional simulations explore differential interference effects of different secondary tasks (held to interfere with different control processes) on the different random generation dependent measures. The work illustrates how the putative control processes may interact in the production of successive responses during the random generation task

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