• Philosophie,

History of aphasias
An anatomy of expression

Denis Forest

Histoire des aphasies

Histoire des aphasies

Histoire des aphasies

The general introduction offers a presentation of the book and explains what its purpose is. Canguilhem is well-known both for his groundbreaking study of the history of reflex action and for his critical attitude towards psychology and brain science. From a philosophical point of view, to reconstruct the history and current development of neuropsychology is to adopt a very different stance. Instead of focusing on how the central nervous system provides automatic responses to (mainly) external stimulations, leaving aside the autonomous, thinking self, neuropsychology suggests considering the brain as the source of a certain number of abilities of which the individual speaker, perceiver or agent takes advantage in the cognitive, expressive or communicative activities that are essential to him. Focusing on the brain, then, is not diminishing or threatening the autonomy of the self. It is rather trying to explain where the powers we have and we constantly rely on really come from. Because of the special role we readily ascribe to language in our mental life, and because of the importance of medical investigation of brain dysfunction in the historical development of brain knowledge, aphasias deserve a special attention in this context.

Chapter I revolves around Broca's discoveries concerning the relations between brain and speech. Its aim is to answer the following question: in a sense, there had been medical reports of acquired speech defects since ancient Egyptian and Greek medicine; the relation between brain and speech had been hypothesized for a long time; so what exactly happened in the XIXth century at the time when aphemia and aphasia proved to be crucial to the beginnings of scientific neurology? One part of the answer is: the scientific investigation of the natural world led between the XVIIIth and the XIXth century to a new vision of man's special abilities. In the context of this naturalistic approach, these distinctive abilities could be conceived as supervening on biological or physiological features. Accordingly, it was no longer sufficient to consider brain structures as mind-related; what had become necessary was to determine if and how brain structure and action could explain specific human abilities. So the importance of Broca comes from the following:

  1. he saw lucidly that a distinction could be drawn between Gall's valuable general claim (there is some kind of functional localization in the brain) and his misguided special, that is, phrenological, claim;
  2. he was convinced that the proper way of giving an explanatory value to brain knowledge was to start with medical, lesional accounts of acquired malfunctions;
  3. he saw that speech, as a distinctive human capacity, gave all its importance in this context to speech defects etiology;
  4. in defining what this etiology was, Broca not only founded a new science of the brain, he gave the first significant element of an answer to this fundamental question : how far can we extend the knowledge of man, while exclusively relying on the knowledge of the human body?

The chapter is concerned both with the logic of Broca's discovery and with the current debate on the multifunctional character of the speech area he identified.

  1. It is wrong or incomplete to analyze Broca's neuropsychological research as strongly context-dependent: Broca's concern with anthropology (in a broad sense) has to do with his reasons for suggesting (in Hanson's sense) that there are special brain correlates of distinct human abilities, and not with his (or our) reasons for accepting a claim as to what (or where) they are.
  2. One essential aspect of the debate on the human brain in the XIXth century was: is a biological or natural knowledge of man possible or relevant (as compared to what a sociological knowledge could be)? Interestingly, this question has resurfaced with the presence of so-called mirror neurons in Broca's area. Some of the neurological correlates of linguistic abilities can be seen as parts of a system that deals with imitation and action understanding. Consequently, current neurophysiology suggests that we may not have to choose between biological reduction and emergence of social practice.

Chapter II is concerned with the question of the analysis of linguistic performance of aphasic patients. It can be argued that language disturbances can be mapped to normal language processing if a) we make realistic assumptions about what such processing consists in and b) if we try to identify where we should localize the damage, not directly in the brain, but in the abstract model of its activity, that is, the corresponding cognitive architecture.

I. In the first part of the chapter, Jackson's account of aphasic speech is construed as a first attempt to correlate brain physiology with assumptions about the making of a sentence. I argue that a) his main debt to Spencer is the transposition of the survival of the fittest motive into a new formula, survival of the fittest states, and that this should prevent us from understanding dissolution as simply opposed to evolution (Jacksonian dissolution is rather incomplete physiological evolution, that is, suboptimal brain functioning); b) his characterization of normal versus aphasic speech has more to do with a pragmatic account of language use than with a formal, linguistic approach to speech.

II. In the second part, I focus on the recent development of models of linguistic performance (as opposed to linguistic competence) and their application to aphasic speech. The main points are the following: a) levels as understood by psycholinguistic research deserve a realist, rather than instrumentalist, construal: for instance, producing a sentence has something to do with understanding what its genuine components are, which shows that sentence production and sentence parsing are tightly linked; b) the standard competence/ performance distinction is discussed and criticized in the context of agrammatical speech. In cases where metalinguistic knowledge of rules seems intact, but no power to generate actual sentences remains, it is questionable to claim that performance only is defective and competence is itself preserved. c) Often, aphasic speech can not be analyzed in negative terms like defects, failures and the like. Some errors make sense when we realize that what is at stake is achieving one part of the speaker's communicative intentions at the expense, for instance, of strict rule following.

Chapter III deals with two closely related questions. The first (and main) question is the classification of aphasias; the second is psychological and neurological associationism. The two are closely related because a) in decomposing the speaking brain, Wernicke, among others, has offered an explanation of the diversity of aphasic syndromes based on associationistic claims; and b) in dealing nowadays with the question of why a realistic account of aphasias can never rely on clear-cut distinctions (because of the dynamics of change, and of the impure nature of defects, which are generally dysphasic, rather than genuinely aphasic), cognitive research may find some help from connexionist modelling of brain activity, which has been somewhat polemically defined as a new version of associationism. Concerning classification, the chapter is concerned with the shift from the initial Wernickean scheme based on a) sensory-motor, physiological distinctions and b) word production and perception, to more recent attempts to focus on a) linguistic distinctions (Jakobson) and b) defects at the level of phrase and sentence construction. Objections to the classificatory project are reviewed. In the end, the best option seems to be to conceive aphasic speech as a linguistic production that approximates the corresponding normal production, being like a blurred picture of the original linguistic competence rather than a testimony of acquired ignorance.

Chapter IV deals with the question of speech perception and so-called sensory aphasia. I follow and analyze the second chapter of Bergson's fascinating and controversial book, Matière et Mémoire.

  1. The proper context of Bergson's urge to challenge the claims of neurology is the shift from a psychological to an organic definition of memory, with the parallel between genetic inheritance and the brain power of retention of past events (Hering).
  2. The main point for Bergson is less memory itself than the question of perception as a spontaneous activity (the power of perception seen as a categorizing power), and it is for this reason that he rejects materialistic accounts of speech perception and its defects. He rejects material categorization of meaningful sequences of speech sounds even more strongly than material memory. But in doing so, he conflates what neuroscientific knowledge (as known to him) can not explain with what the brain cannot do. In this case, instead of reading Bergson as somebody who explains why neuroscientific knowledge cannot succeed, we could read him as somebody who explains the conditions under which neuroscientific knowledge could be accurate, and which challenges are to be met.
  3. I draw a series of parallels between Bergsonian concepts and contemporary psychological and neurocognitive research: in particular, a) the distinction between dorsal and ventral visual systems (which has a close resemblance to his distinction between automatic and attentive kinds of object recognition); b) Liberman's motor theory of speech perception (reminiscent of Bergson's views on the role of a motor scheme) and c) top/down models of perception (that do not contradict Bergson's enactive view of perception as something we do rather than something that happens to us, or in us).
Chapter V deals with aphasias as consequences of pathological states. It includes an historical and a philosophical part.
  1. Very often, Goldstein's conception of aphasias is oversimplified as if he were rejecting (as Head does) classical neurology. The reason why he is the leading figure of neuropsychology in the first half of the XXth century is that he planned a reconstruction, rather than a rejection, of classical neurology, taking into account patients' endeavours to deal with their aphasic and/or cognitive impairment, without denying that decomposition and localisation are legitimate heuristic strategies in neuropsychology, if put in proper perspective (see the foreground/background distinction).
  2. I discuss briefly Boorse's biostatistical theory of health and its ability to offer a proper understanding of aphasic disorders as a genuine malfunctioning of the linguistic capacity. The claim that aphasia is a kind of dysfunction (function being taken, for instance, in the sense of the etiological theory) is too strong because a) it is after all far from clear that there has been in the evolutionary past a specific, genuine selection for language, or for some of its features, that would allow its adaptive understanding as something stronger than a preliminary working hypothesis; b) the proper measure of aphasias as disorders of the speaking brain is rather, whatever evolutionary story turns out to be true, that language is normally involved as a condition for the achievement of a series of tasks that matter to speaking individuals, whatever the biological significance of such tasks may be.

1. The general conclusion of the book is concerned first with the kind of knowledge that cognitive neuroscience provides of the speaking brain. I do not deny that we are free to conceive linguistic creatures that would be, physically, very different from us, and that neuroscience provides at best statements of contingent truths. But I doubt that legitimate scientific causal explanation necessarily involves genuine reduction.

2. Finally, what do aphasias suggest about the vexed question of language and thought? The answer could be that it is not because aphasias are not general mental disorders that they offer empirical support to the thesis of a mutual autonomy of linguistic and thought processes. On the contrary, recent research suggests that aphasic patients have problems with definite kinds of non-linguistic tasks, which could mean that some special linguistic and non linguistic capacities may depend on common processing resources. Saying this is tantamount to saying that aphasias do not simply help identify brain correlates of linguistic abilities, or help identify the architecture of the language faculty, as if we had to take for granted that the language faculty exists as a self-sufficient entity. Aphasias suggest a way to obtain, beyond the received or phenomenal distinction between what is linguistic and what is not, a kind of decomposition of the mind/brain that may be more faithful to its actual functioning.

[Je remercie Tracy Cooke pour la relecture de cette version du résumé]

Denis Forest
Université Lyon 3 IHPST, Paris

PUF - Collection 'Pratiques théoriques'
ISBN 9782130551225 - Parution 2006 - Prix 23 €