What are the advantages and limitations of a cognitive neuropsychology approach to development disorders?
What are the advantages and limitations of a cognitive neuropsychology approach to development disorders?
Cognitive psychology is interested in the mental processes which are responsible for basic cognitive activities (producing language, people and object recognition, information storage). It also has an interest in higher level cognitive processes. Cognition in this way is most commonly investigated by studying individuals with normal cognition. An alternative way of studying cognition is to look at individuals who have disorders of cognition, either developmental or acquired. It is this way of studying cognition that has become known as cognitive neuropsychology. Cognitive neuropsychology, evolved when the fields of cognitive psychology and neuropsychology realised that patients with brain lesions were valuable in the study of and testing of, theories of normal cognition.
Adult cognitive neuropsychology models are based on acquired disorders that occur within pre-existing systems. An acquired disorder is one that has caused impaired cognition in an area which had previously been normal. In contrast to this, cognitive neuropsychology applied to children is concerned with constructing models where functional lesions are found within developing systems. A developmental disorder of cognition applies when an individual has not been able to acquire a cognitive ability to a normal degree. Investigating people with either acquired or developmental disorders of cognition can be used to support or challenge theories about cognition and also to contrast developmental models. The aim of cognitive neuropsychology when applied to children is to develop a model of cognition, whereby all childhood cases of disorders (within that domain) can be explained (Bara, B. 1995).
To explain the cognitive neuropsychological approach to developmental disorders, the assumptions and fundamental beliefs of the approach will be discussed. By studying brain-damaged individuals to gain an understanding of how the normal brain processes information, cognitive neuropsychology is making three assumptions (Margolin, D, I. 1992). Firstly, that information processing modules can function independently (Morton, J. 1981 cited in Margolin, D, I. 1992), Secondly, that brain damage can impair modules differentially (Caramazza, A. 1984 cited in Margolin, D, I. 1992) and thirdly, that observing behavioural consequences of damage to a module, or set of modules, reveals how it (or they) function in the normal brain (Caramazza, A. 1984 cited in Margolin, D, I. 1992). Should any of the above not be so, cognitive neuropsychology would be insufficient in explaining developmental disorders.
Cognitive neuropsychology places emphasis on rare cases that have unusual patterns of deficit. The reason for this is that an individual case of disassociation can be more theoretically informative than many cases with multiple impairments. Coltheart, M (2000) argues this is because the individual case can demonstrate a lack of logical dependence between the deficits. Bishop D, V, M. (1997) argues that single case methodologies are not useful in studying associations, as it is not possible to establish which correlated impairments are 'chance associations' and which correspond to reliable patters of co-occurrence.
One of the core assumptions of cognitive neuropsychology is modularity. According to the modularity hypothesis, multiple cognitive processes or 'modules' make our mental life possible (Ellis A, W. & Young A, W. 1991). Modules are distinct, so brain injury can affect one set of modules whilst not affecting any others. Consequently a patient may experience difficulty with face recognition, but have no problems with reading. Fodors (1983) use of the term modularity is quite specific. Fodor, J (1983) listed what he believed to be properties of cognitive modules. Perhaps the most important of these properties was what came to be known as informational encapsulation (Bara, B,G. 1995). This refers to the fact that a module must carry out its own processing, separately to the processes going on elsewhere in the cognitive system. Fodor, J. (1983) also argued that modules are domain specific, each module can only accept one particular sort of imput.
Fodors (1983) view of modularity has only been loosely accepted by cognitive nueropsychologists today. If Fodors (1983) informationally encapsulated modular system was to be accepted, it could be deducted that identification of a primary deficit influences all later stages of processing. Bishop critiques the view of modularity, in relation to language development, suggesting that such a 'bottom up' mode may only be applicable to the developed adult, where language has been fully established. Such a model is considered by Bishop D, V, M. (1997) to be unrealistic in its application to language development in children, where there is ...
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Fodors (1983) view of modularity has only been loosely accepted by cognitive nueropsychologists today. If Fodors (1983) informationally encapsulated modular system was to be accepted, it could be deducted that identification of a primary deficit influences all later stages of processing. Bishop critiques the view of modularity, in relation to language development, suggesting that such a 'bottom up' mode may only be applicable to the developed adult, where language has been fully established. Such a model is considered by Bishop D, V, M. (1997) to be unrealistic in its application to language development in children, where there is stronger evidence of top-down processing. Further criticism is offered by Hulme, C. & Snowling, M. (1992) (coming from a connectionist theory) (cited in Bishop D, V, M. 1997) who suggest that modularity is potentially achievable in the developed adult brain, but not in the developing child's brain. In the developing system reliance is made on interaction between systems. This interaction is problematic in finding a concrete direction of causation when multiple deficits are found in children with developmental disorders. Bishop D, V, M. (1997) concludes that by simply accepting the earliest stage of development at which the impairment is seen, you are ignoring the evidence which suggests there is interaction between processes. For example in language development, it would be more useful to use a model which allows for both top-down as well as bottom-up influences. Bishop D, V, M. (1997) offers the example that syntax and vocabulary are not independent. Consequently, the developing child will have difficulty with vocabulary learning, if they have poor syntactic skills that have led to a reduced access of information about word meaning. If it is possible for there to be functional modularity without anatomical modularity, any brain damage would affect many/all modules. It is therefore suggested by Coltheart, M (2000) that cognitive neuropsychology would be insufficient because a brain damaged patient would never present with functional modularity.
A fundamental aim of cognitive neuropsychology is to discover functional architectures of cognitive systems, because a functional architecture is a configuration of modules, cognitive neuropsychology would be limited in its application to developmental disorders unless cognitive systems actually are configurations of modules in the developing system, in the same way that they are viewed in the field of adult neuropsychology. Fodor, J (1983) suggested that some forms of cognition depend upon cognitive systems that are not functionally modular. If this is correct, these forms of cognition could not be successfully studied by cognitive neuropsychology. However Shallice, T (1984) (cited in Ellis A, W. & Young A, W. 1996) suggests that if the assumptions of informational encapsulation along with domain specifity are combined with an assumption of neurological specifity where modules are discrete, then cognitive neuropsychology is viable. This is because brain lesions will be able to selectively impair certain modules whilst others are left intact.
One important question that has to be addressed is whether development in children takes a single pathway to the assumed common cognition architecture. Should there be diversity along the developmental pathway, and more importantly diversity at the final cognitive architecture, the application of cognitive neuropsychology could be jeopardised, both within the field of developmental and acquired disorders. Temple, C, M. (1997b) points out that, to date, there is no evidence to suggest the existence of different cognitive architectures.
Bishop D, V, M. (1997) suggests that downstreaming has to be considered as a central component when looking at developmental disorders, highlighting that issues of downstreaming are a further limitation of cognitive neuropsycholgys application to developmental disorders. Although there may be one specific fractionation within the major dimensions of functioning (e.g. language, spatial perception, social cognition and so on) it is often observed that within any domain, the findings are rather more complex, revealing interlinked patterns of associated impairments, in contrast to the highly selective deficits associated with acquired disorders. Within the developing child any deficit can potentially affect further development which is downstream of it, this is not the case with acquired disorders in adults with pre-developed systems. An example of this is shown in a case described by Saffran, E, M,. Marin, O, S, M,. Yeni- Komshain, G, H. (1976) (cited in Bishop D, V, M. 1997). They refer to a patient suffering "word-deafness" who was unable to complete tasks requiring perceptual analysis at the phonological level. Semantic and syntactic processes remained intact in his expressive speech, even though he was unable to understand spoken language. He was however able to understand written language. It can be understood from this that he was able to gain a representation in the form of a sequence of words from the written imput, enabling him to bypass the need for auditory and phonological analysis. However, should a child, in the early stages of language acquisition, have a problem decoding speech sounds, it could be expected that this would lead to impairment at all subsequent levels. This is because the systems that would normally be responsible for vocabulary learning and grammar master would not receive the adequate imput. It could therefore be expected that the child would have difficulty in learning to read as a result of the necessary substrate of spoken language not having been acquired. According to Bishop D, V, M. (1997) it is inevitable that children have associated deficits, due to the interdependence of different stages of processing in development.
A strength of cognitive neuropsychology is that it allows for downstream effects to be explored, allowing theories to be refuted should initial impairments be present without subsequent deficits. Downstream effects come into play when a component of a processing system is needed before a later stage can be activated and where the initial stage is selectively impaired. Consequently downstream effects affect both adults and children in cognitive neuropsychology. Temple, C, M. (1997a) explains that downstream effects reduce both the expression of double dissociation and the degree of transparency of the effects of disorders in determining any specific module that is selectively disrupted. Temple, C, M. (1997b) argues that problems are also associated with downstream effects in the analysis of adult cognitive neuropsychology as well as that of developmental disorders in children.Work by Young, A W. & Ellis, A ,W. (1989) suggest it could be argued that downstream effects found in some acquired disorders are similar to that found in developmental cases (cited in Temple, C, M. 1997b).
Coltheart, M (2000) suggests that cognitive neuropsychology assumes that brain damage can only lead to subtraction from the system, but cannot add to it (this assumption stems from Fodors (1983) theory of subtractivity). If this were not the case then nothing could be learnt about the normal system by studying damaged ones. There is evidence to suggest that the brain has a certain level of plasticity. Saffron E, M. (1982) (cited in Temple, C, M. (1997b) discusses that should the brain reorganise and generate new modules then abnormal performance could not simply be a reflection of a normal system without the disrupted component, which is the basic assumption of cognitive neuropsychology. Thus the application of cognitive neuropsychology to childhood development disorders would be considerably weakened. The concept of plasticity in the early child has arisen as a result of observations which have shown children developing specific abilities/functions even when the area of the brain thought to control these functions has a deficit. Work by Carlson, J,. Netley,. & Pitchard, J. (1968) (cited in Temple, C, M. 1997b) show the extent of the developing brains plasticity. However, the methodological quality of these studies has been challenged by Bishop D, V, M. (1997). Any evidence for plasticity makes the application of cognitive neuropsychology more problematic. However, Temple questions some of the previous evidence surrounding plasticity, which strengthens the case for cognitive neuropsychologys application to developmental disorders in children.
Bishop D, V, M. (1997) suggests that cognitive neuropsychology cannot appropriately be applied to developing dynamic cognitive systems in children as appropriately as it can be applied to static adult systems (although this is criticised too). Temple, C, M. (1997b) challenges this view suggesting that cognitive neuropsychology has been successfully applied to non-static progressive degenerative disorders, like semantic dementia (Hodges, J, R,. Patterson, K, E,. Oxbury, S. & Funnel, E. 1992 cited in Temple, C, M. 1997b). Cognitive neuropsychology has also been useful in the analyses of dynamic recovery. Temple, C, M. (1997b) goes onto suggests that level of dynamisms in the impaired cognitive system of child may be less dynamic than that seen in the healthy, developing cognitive system. From Temples C, M. (1997b) perspective it could be argued that if cognitive neuropsychology can be applied to non-static disorders in adults, that it can also be appropriately applied to children with developmental disorders.
Although the capacity for compensatory reorganisation has traditionally been explained as a result of; substitution or redundancy of neural repair mechanisms, none of these actually suggest a fundamental reorganisation of the cognitive system (cited in Temple, C, M. 1997b). Aram, D, A & Eisele, J, A. (1992) suggest that these proposed mechanisms of compensation appear to have limitations. Temple, C, M. (1997b) suggests that even the neurodevelopment disorders that have previously been considered basically asymptomatic, having undergone thorough analysis, now show deficits where no plastic reorganisation has taken place. One example (cited in Temple, C, M. 1997b) by Lassonde, M,. Sauerwein, H, C., and Lepore, F. (1995) is that pervasive midline disconnection effects can be seen in callasal agencies. Contrary to most work which has shown plasticity as most effective following an early injury, Landau-Kleffner syndrome is one example of a disorder where earlier onset tends to result in a more severe disorder highlighting the limitations of plasticity.
Temple, C, M. (1997b) suggests that the mechanisms of plasticity for many developmental disorders have always been questioned. An example of this is shown with developmental dyslexia. A further argument offered by Temple, C, M. (1997a) is that plasticity may be a response to injury or disease as opposed to abnormal development process. Temple, C, M. (1997a) highlights recent studies that have confirmed children with developmental disorders may have focal cognitive abnormalities in a variety of cognitive systems, such as; reading, spelling, arithmetic, face recognition and executive systems amongst others (e.g. Temple, 1985, Temple et al., 1996, Temple & Marshall 1983 cited in Temple, C, M. 1997b). Again the evidence put forward by Temple, C, M. 1997b, strengthens the case that cognitive neuropsychology can be appropriately applied to developmental disorders.
Other properties suggested by Fodor J, (1983) were that the operation of modules are mandatory, this view is less unanimous than the view of information encapsulation, mandatorieness is more a property of input modules than output modules according to Ellis A, W. & Young A, W. (1996). The idea that modules are innate has also been heavily criticised. Fodor J, (1983) originally proposed that any cognitive process with the characteristics of domain-specifity and information encapsulation, had an innate biological base which had undergone evolutionary adaptation. Modular explanations of specific language impairment (SLI) have shown that twin studies have provided evidence that SLI has a genetic basis, and also shown in some cases that a single defective gene could be responsible (North, T., Donlan, C. 1995, cited in Bishop D, V, M. 1997). Jackendoff, R. (1993) (cited in Bishop D, V, M. (1997) also suggests that SLI can be seen in terms of an innate grammatical module. Jackendoff, R. (1993) argues that the evidence is strongly weighted in favour of an argument that impairment is genetic, this impairment is able to affect one ability (construction of mental grammar) whilst leaving other cognitive abilities intact.
In contrast to the above views of modularity, models of development processes suggest modularity, in the terms of domain-specifity and information encapsulation, is the result of experience (Elman et al 1996 cited in Bishop D, V, M. 1997). Bishop D, V, M. (1997) suggests that cerebral specialization is as dependant on specific experience as it is on pre-wiring, just because a genetic basis of SLI is compatible with a deficit in an innate grammatical module, it should not necessarily, according to Bishop D, V, M. (1997), be taken as evidence for an innate model.
The topic of language disorders has been discussed and shown as evidence to substitute both arguments for and against the use of a cognitive neuropsychological approach to developmental disorders. It could be argued that a cognitive neuropsychology approach to this topic is more suited than the traditional developmental models which tend to rely on the description of stages, through which the child must develop. Although these developmental stage theories are useful in explaining the aspects of mastery a normal child will develop, they are less useful in explaining the broad range of language disorders. The cases discussed by cognitive neuropsychology with relation to developmental disorders tend to involve children that don't just present simple cases of developmental language delay, but present unevenness in their linguistic development.
It can be seen from the evidence put forward that there are both numerous similarities as well as differences between cognitive developmental disorders and acquired disorders, seen in adults. Cognitive neuropsychology is somewhat limited as a result of the evidence put forward with regard to functional plasticity and downstream effects. Although downstream effects do not disprove theories of a modular cognitive system, but they do make the appearance of classical double dissociations difficult to attain within developmental disorders (Temple, C, M. 1997b). One strength of cognitive neuropsychology is its use of case studies. This allows for children to be identified with the initial impairment without subsequent downstream effects, supporting cognitive neuropsychologys application to developmental disorders. It must be noted that areas of cognitive neuropsychology that have undergone criticism in its application to developmental disorders have, more often than not, experienced similar difficulties in its application to acquired disorders. Only time will tell if similar obstacles will be overcome in its application to developmental disorders. It could be argued that some of the theories assumptions cannot be proved, (Ellis A, W. & Young A, W. 1996 suggest modularity can never be proved or disapproved) but they have to be acknowledged until such time that they are disproved.
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