Contrasting domains in the control of action the routine and the non-routine

Contrasting domains in the control of action: the routine and the non-routine Tim Shallice University College London and SISSA Trieste Correspondence to: T Shallice, Institute of Cognitive Neuroscience, Alexandra House, 17 Queen Square, London WC13AR, UK ((Association Lecture of Attention & Performance XXI:Processes of Change in Brain and Cognitive Development (ed M Johnson & Y Munakata), OUP, 2006.)) Abstract The Supervisory System model in which there are two cognitive levels in the control action is assessed It argued that there is a modulatory relation between the levels It is further argued that standard connectionist variables such as age of acquisition, familiarity and frequency are particularly useful for characterising behaviour produced by contention scheduling, the lower-level system, when Supervisory System function is impaired By contrast, an analogy with symbolic AI models is used to theoretically motivate a fractionation of Supervisory System processing as created by a set of functionally selective and anatomically partially separable subsystems It is argued that the systems for the Supervisory System’s top-down selection of schemas in contention scheduling has a different lateralisation of dorsolateral prefrontal cortex from the systems concerned with non-evident error detection and checking The former are held to be the more left lateralised by comparison with the latter Introduction The idea that there is a hierarchical organisation of the processes that control action with the higher levels modulating the operation of the lower ones is very old, going back at least to Hughlings Jackson Moreover in the more neurobiological versions it is commonplace to view the prefrontal cortex as the summit of the hierarchy (e.g Luria,1966; Fuster, 1989; Dehaene & Changeux, 1997; Miller & Cohen, 2001.) A second very common idea in experimental psychology is that there are two domains of the control of action – automatic and non-automatic (controlled) (e.g Shiffrin & Schneider, 1977) - and there are related models in developmental psychology (eg Karmiloff-Smith, 1986) The model of Norman & myself (1980, 1986) (see also Shallice, 1982) essentially combines these two ideas in proposing two domains of processing – that of the Supervisory System and of contention scheduling - with the former only realising its effects through modulation of the latter and with the Supervisory System localised in prefrontal cortex In these respects the Norman-Shallice model may be thought of as merely one variant of the combination of two now standard, although not universally accepted, perspectives in cognitive neuroscience It has, though, an additional rather different conceptual dimension It was developed not only from a conflation of the experimental psychology and the neurobiology of levels of action control; it also represented in two respects an interface between two different modelling traditions - the connectionist, at that time represented by interactive activation modelling (e.g McClelland & Rumelhart, 1981) and of symbolic AI Thus as far as the selection of which schemas control the processing and effector systems they require, contention scheduling, the system the Supervisory System modulates, is viewed as operating in an interactive activation fashion with units corresponding to overlearned single motor or cognitive skills – action and thought schemas In routine mode schemas receive activating input from both higher-level (source) schemas and from object-trigger systems In nonroutine mode additional activation to schemas is provided by the Supervisory System However, in addition it is also useful to conceive of the overall system within a more symbolic framework as operating in an analogous fashion to production systems The symbolic aspect is used principally in the processes that follow selection and in particular how the “arguments” of schemas are set on selection – where, with what and on what the thought or action skill operates – which depend upon the simultaneous state of object representation systems Moreover, the initial verbal account has been realised more recently computationally in interactive activation simulations of Cooper & Shallice (2000) based on the everyday task of coffee preparation The intellectual origins of the Supervisory System concept were different In earlier discussions of the automatic/controlled distinction (e.g Shiffrin & Schneider, 1977) what processes lead to controlled processing was only vaguely specified In the NormanShallice model it was held to be a materially and conceptually separable system Conceptually that different systems could be involved in routine and non-routine operations came from classical artificial intelligence There the idea was quite standard that in addition to the processes used for the effecting of routine selection of routine operations, there are special processes that come into play in situations where routine responding does not lead to the attaining of goals (e.g Sussman, 1975; Newell, 1990) The main thrust of the model developed by Norman and myself (1980, 1986) was to argue for a prefrontally located Supervisory System, coming into play in non-routine situations to modulate the operation of a system which effects routine action – contention scheduling Thus the distinction between the situations in which the two types of system come into play was derived from symbolic AI One may view the contrast in the computational principles on which the two systems operate from a related but not identical perspective Perner (2003) has argued that the lower-level system representations involved in contention scheduling are implicit, as they are procedural representations By contrast he argues that the higher (Supervisory) level “is defined by the necessity to entertain predication and fact-explicit representation and to exercise content control over the lower level” (p225) He illustrates this with the example of a child given the instructions ‘Put the green cards into the left box’, where the child cannot represent their meaning in a ‘predication-implicit’ way, as no card is actually being presented He continues “That also means that not only predication to instances but also that they are not real but only hypothetically considered instances needs to be made explicit … The same explicitness is, of course, also required for planning, reasoning and entertaining hypotheses before one can come to a conclusion which action sequence is best to employ.” (p225) It is possible to consider the computations carried out by the cognitive subsystems on two dimensions One concerns the number of input variables that need to be taken into account and the complexity of their interactions As these increase computational procedures which optimise constraint satisfaction, ones using gradient descent principles are likely to be optimal ie systems operating on broadly connectionist principles, of which interactive activation models are a simple version The second dimension is the degree to which the values of intermediate products, of input variables themselves, and indeed which are the critical input variables may be subject to revision As this characteristic increases so the value of having explicit how and why intermediate products are arrived at becomes increasingly valuable One basic theme of the paper is that high values on the first dimension are more critical in the computations of contention scheduling and high values on the second for those of many aspects of the Supervisory System More recently the model has been developed by Stuss et al (1995) and Shallice & Burgess (1996) to confront a major conceptual inadequacy in the original model How the Supervisory System enabled the organism to confront non-routine situations was completely unspecified Thus the concept is derided by Dennett (1998) as ‘an ominously wise overseer – homonculus who handles the hard cases in the workshop of consciousness’ (p288) Since the logic of the original paper was partially derived from the idea that the postulating of homunculi of reduced power could be progressive, itself derived from Dennett (1978), the source of this criticism was rather odd However the sentiment was common (see e.g Baddeley, 1996) One major strand of development of the model has been to confront this objection However this has principally been done by analogy with the deeply unfashionable conceptual framework which was critical in the initial development of the model, namely symbolic artificial intelligence The essence of the Mark II model of Shallice & Burgess (1996) was the assumption that in confronting non-routine situations a number of qualitatively very different types of computational operations are required which were held to be the province of anatomically separable higher-level subsystems It further used the assumption of functional specialisation, which can be broadly but unrigorously specified, as that if the phenotype of homo sapiens includes cognitive tasks sufficiently different in their computational requirements from all others in its repertoire then they would be implemented at least in part in separable regions of cortex ((Footnote: For simplicity I will adopt the terminology of the ShalliceBurgess paper.)) Four interlinked issues are addressed through the paper One major issue is whether the distinction between higher and lower-level control of action is well captured by the idea of their being the provinces of different systems with ‘modulation’ being an appropriate characterisation of their relation The second major issue whether “routine-ness” is an appropriate concept to use to contrast the different properties of the two levels of systems The third concerns the relevant saliency of the constraint satisfaction and explicitness dimensions respectively Thus I will argue that a broadly connectionist framework is particularly useful in characterising the lower-level contention scheduling system, as discussed above This is considered in the next section Then I will address whether symbolic AI ideas are of value when considering the Supervisory System; in particular I will consider the perspective derived from symbolic AI that the” ominously wise overseer-homonculus" can be tamed by its being fractionated into different subsystems This is addressed in the following two sections The final issue, considered in the last section, is whether the division relates to the phenomenological one between willed and automatic action Basic Findings: Associationism and Contention Scheduling In functional imaging, that the activation of prefrontal cortex declines as tasks become less novel has been shown in a variety of paradigms (e.g Raichle et al.,1994; Jueptner et al, 1997) Moreover lesions to prefrontal cortex affect the ability to confront non-routine situations appropriately (e.g Shallice & Evans, 1978; Knight, 1984) This fits with a prefrontally localised system being critical for non-routine tasks However while the absence of such evidence would undermine the current approach, it could be explained in a variety of ways; for instance non-routine situations may make greater demands on working memory Stronger evidence is provided by the findings that lesions to prefrontal cortex lead to behaviour characterisable as that controlled by contention scheduling alone Through the last 100 years of its history psychology has been concerned to model routine operations – initially through S-R psychology, then somewhat separately in more computational form through production systems and in a more neurobiological one through connectionism A key aspect of the model is the role that stimulus-response (action schema) associations play in the genesis of action For such frameworks, factors such as frequency, familiarity, age-of-acquisition, priming, interference and so on become important dependent variables Predictions made from accounts of contention scheduling inherit this tradition A key aspect of the model is the role that stimulus-response (or better trigger-stimulus representation to action-schema) associations play in the genesis of action So prefrontally impaired behaviour should be especially sensitive to: (i) familiarity, (ii) ageof-acquisition and (iii) (implicitly) frequency-of-application of a rule In a variety of prefrontal syndromes the patient’s actions are behaviours triggered by stimuli with which they are strongly associated even when they have been instructed not to respond in this way and gain nothing by so doing These include the grasp reflex (De Renzi & Barbieri, 1992), utilisation behaviour (Lhermitte, 1983; Shallice et al, 1989), the anti-saccade type of tasks (Paus et al, 1991) and forms of the anarchic hand syndrome (Della Sala, Marchetti & Spinnler, 1991; Humphreys & Riddoch, 2003) In such syndromes action selection can be at the level of effector selection (Riddoch et al, 1998) or of so-called ‘source’ schema (Shallice et al, 1989) The analogue of these behaviours in problem-solving is the especial vulnerability of frontal patients in situations in which the elicitation of ‘capture errors’ (Reason, 1979; Norman, 1981) is potentiated by stimulus displays (Della Malva et al, 1993) In other words prefrontal patients have difficulty in suppressing inappropriate responses triggered by familiar S-R bonds in contention scheduling; they cannot overcome potentiated but incorrect responses A second relevant problem-solving phenomenon is the strikingly good performance of prefrontal patients in situations where rule abstraction is required if the rule is one which corresponds to the inbuilt tendencies of the contention scheduling system Thus Verin et al (1993) found that an alternation rule was attained more rapidly by prefrontal patients than normal adults when the subject must make one choice once every 15 seconds; the prefrontal patients made virtually no errors Moreover 5- and 6year old children but not those of 7+ also found the task very easy (Houde et al, 2001), supporting the assumption that the contention scheduling system obeys age-of-acquisition principles Where frequency is concerned perhaps the most direct support is provided by the use of the random generation task In the random generation task the subject must produce a sequence of numbers which approximate randomness as closely as possible; that is the responses must not satisfy any given rule inappropriately frequently Baddeley (1986) analysed the task He argued that as there were no external stimuli, any schema controlling obeying a rule which is operating to elicit any one response must be inhibited prior to the next response and an alternative schema activated On the model both these steps would require the Supervisory System Jahanshahi et al (1998) showed that by 10 Closely related to this view are two other positions Jack and Shallice (2001) argued that the basic idea can be generalised to any conscious state They argued that to be conscious of anything depends on the occurrence of what they call a C-process (for consciousprocess) A C-process is the key supervisory subprocess that leads to the selection of the dominant schema and the setting of its arguments in contention scheduling The perspective that conscious experience is critically linked to the operationw of the Supervisory System that by top-down modulation lead to schema selection in contention scheduling (Jack & Shallice, 2001) fits with cognitive neuroscience evidence that when one becomes conscious of a percept prefrontal systems become activated (Lumer & Rees, 1999) Perner, too, develops his arguments about the need for the use of explicit representations in the operations of a Supervisory System He argues that as conscious awareness implies that we know what we know that this entails that his so-called “predication-explicitness” is a prerequisite for conscious awareness, and that the same applies for “factexplicitness” He continues “Fact-explicit representations minimally constitute some meta-awareness of what one knows, which satisfies the basic intuition behind the higherorder thought theory (of consciousness) that being consciously aware of a state of affairs entails knowing (or thinking) that one knows” (p230) In other words the properties required of a Supervisory System to carry out the types of operation that are prototypic of it, mean that the representations used by it to activate schema in contention scheduling have properties that conscious representations need to have and plausibly ones which would require they be conscious 34 The phenomenological distinction between willed/conscious/explicit and ideo-motor (in the sense of James (1889)/automatic/implicit thus provides parallels to the processing contrast of the two different ways in which schema selection can occur in contention scheduling, that is with or without Supervisory System modulation The argument of the paper is that there are two very different types and levels of processing domain in the cognitive control of action depending on the routineness and/or implicitness of the type of operation Thus variables typical of connectionist systems characterise the operation of contention scheduling in the absence of the Supervisory System Turning 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The effect of a fixed foreperiod of or s (from Stuss et al, in press) (LL = Left Lateral; RL = Right Lateral; IM = Inferior Medial; SM = Superior Medial; CTL = Controls) The comparison between RT to a short foreperiod (3-4 s.) and to a long (6-7 s.) one in the variable foreperiod condition of Stuss et al (in press) (for groups see the legend to fig 5) 44 MRI scan 6-years post-injury of the patient with the most focal lesion in the study of Shallice & Burgess, 1991 The lesion principally involves Brodmann areas 10 and 11 45 46 47 48 ... involved in routine and non -routine operations came from classical artificial intelligence There the idea was quite standard that in addition to the processes used for the effecting of routine selection... paper is that there are two very different types and levels of processing domain in the cognitive control of action depending on the routineness and/ or implicitness of the type of operation Thus... sequence of implementable steps (v) The fifth is the realisation of the steps as actions (vi) The final one is the checking that these actions are indeed ameliorating the situation, that is they