4. Análisis e interpretación de la información recopilada y resultados de la evaluación.................... 17 2
4.4 Alcance de indicadores previstos y su pertinencia
ous occasions, that it is rude to point, and it there- fore may come as something of a surprise to learn that one recently documented double dissociation relates to pointing. Back in 1922 the term ‘auto- topagnosia’ was coined to refer to the condition in which a person is unable to point to their own body parts when given a verbal command. This has got nothing to do with shyness or anything of that sort, but seems to have a lot more to do with impair- ments regarding how information regarding body parts is represented internally. In exploring this and related disorders, Felician, Ceccaldi, Didic, Thinus- Blanc and Poncet (2003) tested a variety of elderly
people on their ability to carry out several simple tasks. The results are shown in Table 2.1.
JR are the initials of a 73-year-old right-handed male who presented with a recent history of being unable to perform accurate motor movements (such as writing and dialling telephone numbers) with his right hand. AP are the initials of a 68-year- old right-handed woman. Until the age of 55 she had worked as a cashier, but she presented with a recent history of making spelling and calculation errors. She also presented with difficulties regard- ing knowledge of the spatial disposition of body parts (Question: ‘Is the shoulder above or below the knee?’ Answer: ‘?’).
developmental disorders Neurological problems that develop as a person ages. Typically such problems are noted in childhood and may arise as a result of genetic factors, during pregnancy or birth.
acquired disorders Neurological problems that arise during the normal course of development through injury or illness.
Both patients and a group of age-matched con- trol participants were tested across the battery of simple tasks shown in Table 2.1. The notation x/y refers to the numbers correct (i.e., x) out of a pos- sible total (i.e., y). Clearly the age-matched controls performed generally at ceiling in all cases. However, an interesting double dissociation can be seen across certain of the tasks for JR and AP (see the cells in Table 2.1 in bold).
Whereas JR was (essentially) unimpaired in his ability to point to the body parts of someone else, he was (essentially) unable to point to his own when asked to. In contrast, AP was impaired in being able to point to the body parts of someone else, but she was quite able to point to her own.
The deficits of neither patient could be traced to problems in pointing per se, to follow verbal
commands or, indeed, name body parts. For JR his problem was diagnosed as being a classic case of autotopagnosia. His problems concerned either some form of corruption in the manner in which he represented his own body parts, or some form of difficulties in accessing this information (or indeed both).
In contrast, AP was diagnosed as having ‘hetero- topagnosis’ – an inability to point to the parts of other people’s bodies. In turning to her case, Felician et al. discussed the possibility of a specific module dedicated to processing information about other people’s bodies (p. 1313). In AP but not JR this module was damaged. By extension, a separate module that codes information about one’s own body parts is needed to explain the double dissociation. This module was impaired in JR but not AP.
Table 2.1 Summary data of performance of the patients and control participants across a range of simple pointing tasks
JR AP Controls
Naming body parts
Own (visual input)a 20/20 20/20 20/20
Own (tactile input)b 20/20 20/20 20/20
Others (visual input)c 20/20 20/20 20/20
Pointing to body parts
Own (verbal command) 4/20 20/20 20/20
Others (verbal command) 18/20 3/20 20/20
Pointing to objects
Objects within reach 20/20 20/20 20/20
Object in the room 20/20 20/20 20/20
Pointing to parts of pictures
Parts of an animal 12/12 12/12 12/12
Parts of a bike 20/20 16/20 20/20
Parts of a human body 20/20 20/20 20/20
Notes: aRefers to a task in which the examiner pointed to the participant’s own body parts to name. bRefers to a task in which the examiner touched the participant’s own body parts to name. cRefers to a task in which the examiner pointed to his own body parts for the participant to name.
Source: Felician, O., Ceccaldi, M., Didic, M., Thinus-Blanc, C., & Poncet, M. (2003). Pointing to body parts: A double dissociation study. Neuropsychologia, 41, 1307–1316.
logical evidence. Nevertheless, it seems that each kind of deficit that we have described – association deficit, single dissociation and double dissociation – poses problems for interpretation. Caution therefore must be exercised.
Others have been even more sceptical. For instance, Gregory in 1961 voiced some concerns over just how much a broken brain can possibly tell us about a normal brain. Think about it. Remove the fuse box from your car and none of the electrics will work. So not only do the lights, heater and CD player no longer work but neither will the engine. In this rather extreme example, therefore, observing the behaviour of this broken car will tell us almost nothing about the normally functioning car.
Gregory (1961), though, was much more con- cerned with the brain on the understanding that this is a very complicated ‘machine’. As he stated, if a single component is removed from a complex, multi- component machine, ‘anything may happen’ (p. 320). He continued by saying that a typical finding with electronic equipment (remember, this was written in the early 1960s) was that ‘several different faults may produce the same “symptom” . . . anything affecting the (power) supply will tend to produce the same fault’ (p. 322). Here the example was of removing some resistors from the radio set with the consequence that the radio begins to emit howls. So what should we conclude from such a demonstration? Gregory was at pains to point out that it should not lead to the con- clusion that the function of the resistors is to suppress howls. Yet similar claims about inhibitory mechanisms are occasionally made by neurophysiologists when discussing damaged brains!
In developing his argument, and in providing such examples, Gregory was actually building a case for
functionalism. As he stated, understanding the proper-
ties of a damaged machine is made considerably easier if a functional account of the intact system is available. In this regard, cognitive neuropsychology will be made much easier if functional accounts of the normal intact system are available.
So where does all of this leave us? Well, perhaps the most obvious conclusion to be drawn is that it would be folly to try to defend a whole theory of the archi- tecture of the mind on the basis of just one result – be it an association deficit, a single dissociation or even a double dissociation. Statements about functional architecture are generally on a much firmer footing if backed up by a whole range of (what is known as)
converging evidence. Our theory of mind ought to be
consistent with a range of phenomena and be testable
control participants A group of individuals with intact brains who provide a profile of normal performance on some test or battery of tests in a cognitive neuropsychological study.
association deficit A neuropsychological case in which an individual with brain damage presents with deficits in two different domains such as an inability to understand (i) written and (ii) spoken forms of language.
single dissociation See dissociation deficit.
dissociation deficit A neuropsychological case in which an individual with brain damage presents with a marked deficit in one domain but has preserved, or relatively preserved, function in a related domain. For instance, a person is able to read words but not non-words.
mental resources The mental equivalent of energy or power that supports cognitive performance in some task. Difficult tasks are assumed to demand more mental resources than simple tasks.
resource artefacts This refers to accounting for a single dissociation by claiming that task difficulty is not equated across the various tasks that show the dissociation.
double dissociation Where individual 1 performs well on task A but poorly on task B, but individual 2 performs poorly on task A but well on task B.
Concluding comments
In the second half of the chapter we have gone some way to introduce you to the basic modularity of mind hypothesis. This is because it provides the founda- tions for much of what is to follow in the rest of the book. In large part we will accept the view of the mind set out by Fodor (1983) and, as we proceed, we will attempt to see how well this view is supported by the evidence.
The final sections of the chapter have been con- cerned with the cognitive neuropsychological approach. Like much of present-day cognitive psychology, much of cognitive neuropsychology is wedded to the notion of a modular functional architecture as discussed by Fodor (1983). Although the details of any particular theoretical framework can be debated at length, the notion of semi-independent processing modules crops up time and time again in the cognitive psychology literature and, over recent history, this view of the mind has been bolstered by cognitive neuropsycho-
to the point of being falsified (see discussion of Popper in Chapter 1). Most importantly, the theory must make testable predictions concerning the outcomes of experiments that have yet to be carried out, and obser- vations that have yet to be made. It is by this means that we hope to be able to decide about the appropri-
ateness of our claims about modular decomposition and the modularity of mind.
converging evidence A variety of different forms of evidence that all lead to the same sort of conclusion. The evidence converges on the one conclusion.
CHAPTER SUMMARY
l Three approaches to the study of the mind are the cognitive, artificial intelligence and cognitive neuro-
science approaches. Each has its different methods but the first two are of prime concern here. We are inter- ested in attempting to provide functional accounts of the mind and these can be derived without any discussion of the underlying neurology.
l Information theory (Shannon & Weaver, 1949) provided a means to quantify the amount of information in
terms of redundancy. The theory provided the basis of understanding communication systems in terms of information processing. Within a communication system, information is sent by a source (the sender) via a channel of transmission. Outputs from the channel arrive at a receiver. The efficiency of the communication system can be quantified according to criteria such as channel capacity, rate of transmission, redundancy of encoding and noise. Such proposals formed the basis of characterising human cognition in terms of informa- tion processing theory. A central idea is that external stimuli give rise to sensory signals that encoded them. Such signals can be defined as being internal representations, which stand for or designate external things.
l The computational metaphor highlights similarities between minds and computers. A digital computer is
designed to store, operate on and retrieve large amounts of information characterised as strings of 0s and 1s in something known as binary code. The basic ideas that draw the analogy between computers and minds are set out in the physical symbol system as defined by Newell (1980). Here there is a well-defined set of symbols and a well-defined set of operations, with the overall behaviour of the system governed by a con- trol program specifying the rules of operation. When considering the computational metaphor of the mind, therefore, we must also consider the use of internal representations or symbols that stand for aspects of the external world, internal processes that define operations upon these symbols, and an internal control system (Pinker, 1997). Cast in this way the metaphor becomes the computational theory of mind.
l What the computational theory of mind leads to is the understanding that minds and computers (pro-
grammable devices) are a very special kind of machine. A critical distinction here is between rule-following and rule-governed systems. A rule-governed system is one that acts according to a set of rules that are not represented within the device itself, whereas for rule-following systems, the rules of operation are repre- sented internally in some form. Both minds and computer are taken to be rule-following devices. However, where minds and computers differ is with respect to the formality condition. A computer has no under- standing of what the symbols it is using actually represent whereas minds do comprehend the link between thoughts and the things to which these thoughts refer.
l The formality condition reveals that computational theory can only provide, at best, an incomplete view of
the mind. In offering the physical symbol system as a characterisation of the mind, it is clear that the claim is that mental operations have access only to the form of the internal codes and not their content. The computer has only access to the binary codes and has no conception of what such codes stand for or refer to. Humans, in contrast, typically have immediate access to what they are thinking about and how they are feeling. In this respect the computational theory of mind may be profoundly limited in its scope. Never- theless, the computational theory of mind provides the most currently useful framework for thinking about human cognition and within this framework it is possible to consider how the mind may be constituted.
l Marr (1982) introduced the principle of modular design in which large-scale problems should be decom-
system could be resistant to damage in that if one module stopped working, this would not necessarily entail the whole of the system coming to a standstill. This kind of modular decomposition could be represented by the use of an arrows-and-boxes diagram.
l Alternative ideas about modular decomposition have recurred throughout the history of cognitive psycho-
logy. Horizontal faculties specify generic capabilities that cut across all domains, whereas vertical faculties specify particular domain-specific processes. The most thoroughly developed view of mental modularity is contained in the modularity of mind hypothesis (Fodor, 1983). By this view critical distinctions are drawn between the sensory transducers, input modules and central processors. The input modules can be best understood in terms of special-purpose computational devices: vertical faculties can be seen to fractionate into multi-modular systems. The input modules take stimulus information from the sensory transducers and transform it in such a way that a best first guess as to what is out there can be provided for further ana- lysis. The central processes are responsible for assigning meaning and interpreting the proximal stimulus.
l The assumption of modularity fits comfortably with ideas relating to the breakdown of cognitive pro-
cessing. For example, one of the general assumptions of cognitive neuropsychology is that if individuals experience focal brain damage or lesioning, then this is likely to impact on specific cognitive functions. This can lead to a number of empirical findings such as association deficits in which patients perform poorly on related tests, dissociation deficits in which a patient performs well on one task but less well on another, and double dissociation deficits in which one patient performs well on task A but not on task B whereas another patient performs well on task B but not on task A. Such cognitive neuropsychological data must be treated with care but when it is considered alongside other forms of converging evidence a case can be built for claims about putative modular architectures.
ANSWERS TO PINPOINT QUESTIONS
2.1 The Shannon and Weaver (1949) model is a functional account of communication because the formulation of communication is independ- ent of any form of physical instantiation. 2.2 Information processing theorists are concerned
with abstract events that intervene between the stimulus and responses, whereas discussion of stimulus–response bonds is sufficient for behaviourists.
2.3 The control unit serves to operate upon symbols retrieved from memory.
2.4 A radiator is not a rule-following device because, although it acts according to rules set out by the central heating designer, those rules are not instantiated within the radiator itself.
2.5 Strong AI states that the mimicry of human behaviour is a sufficient condition for having mental processes.
2.6 A modular airplane would be preferable since it might be able to continue flying even if certain parts of the aircraft were not working properly.
2.7 Vertical faculties are domain-specific competen- cies. Horizontal faculties are general competencies. 2.8 A module is domain-specific when it only
responds to a certain type of stimulus.
2.9 The case of Phineas Gage supports a modular view of the mind because the removal of his left frontal lobe seemed to be primarily associated with self-control and while this was compromised after the injury, his remaining cognitive system appeared to function normally.
2.10 A single dissociation (i) may reflect the opera- tions of a modular mind, or (ii) it may simply arise as a result of a resource artefact. Either the brain damage has selectively impaired the oper- ations of one particular module, as evidenced by poor performance on one particular task, or it might be that the particular task examined demands more mental effort to complete than others in the test battery.