This book on language and action in cognitive neuroscience, co-edited by Yann Coello and Angela Bartolo, reactivates a classical debate about language processing in the brain. A traditional view holds that language processing is limited to a set of language-specific neural structures, the anterior and posterior language areas within the left hemisphere. Indeed, this view is supported by clinical observations in patients with language disorders: for example, aphasia of the ‘sensory’ type, whenever a patient fails to understand spoken words and sentences, is generally a consequence of lesion in the medial part of the left temporal lobe (the Wernicke area), whereas aphasia of the ‘motor’ type, characterized by a failure to generate spoken words, is a consequence of the left inferior part of the frontal lobe (the Broca area). Alternatively, a different view holds that language processing is widely distributed across cerebral cortex: This is what this book proposes to explore, namely that the meaning of words is embodied in neural processes that are also responsible for perception and action.
Arguments as to the latter view arise from several sources in the literature. One of these arguments is that the memory for words (the lexicon) is not an undifferentiated store where the words accumulate; instead, it has an internal organization. Words appear to be classified in the lexicon according to the semantic category to which they refer. Clinical observation has shown that patients with selective brain lesions may fail to understand words, or to find the name of objects, from a given category. Such patients may be able to correctly name pictures representing inanimate objects, such as houses, whereas they fail to name pictures representing living things, such as animals or food. These neurological findings strongly support the notion of a distributed representation of semantic processing: indeed, recent neuro-imaging studies show that hearing words referring to colours is associated with increased activity in a ventral area at the occipito-temporal junction known to be involved in colour knowledge, whereas hearing words referring to tactile qualities is associated with activation of the somatosensory cortex.
The present book will extend this notion to the domain of action. Action and language have strong links: not only is language expression (vocal speech or gesture) intrinsically motor, but also language comprehension has been shown in the last decade to involve the contribution of the motor system. This double reality is reflected in the book by chapters distributed into several sections: After an introductory section on embodied cognition, communication and the language faculty, the idea that language evolved mainly from a repertoire of manual gestures is developed. The following section is devoted to experimental studies of the processing of action-related words and sentences. These studies show that the motor system is somatotopically influenced by the linguistic material when its content refers to an action, as revealed by the kinematic analysis of movements that interfere with the linguistic content and by neuro-imaging of the motor cortical areas.
Other sections deal with the issue of the integration of spatial relationships in verbal description and motor behaviour. Important questions are raised: What is the role of spatial and motor experience in language acquisition? How is space encoded in verbal descriptions and behavioural tasks by children at different ages? Are spatial language and perception/action associated with the same or different underlying representations? What is the influence of object properties on the use of spatial demonstratives during the apprehension of spatial descriptions? What are the relationships between number processing, space processing and action?
Finally, the frequent co-occurrence of speech and expressive gestures or pantomimes offers the opportunity to discuss the features that are common to both language and action. This is done in the following section at the level of the neural structures involved, by using neuro-imaging tools, demonstrating that the time course for integrating (in the left inferior frontal cortex) the linguistic meaning carried by speech or gestures is the same. But this is also done in pathological populations where the expression and/or comprehension of meaning are affected – in dyspraxic or autistic children. These descriptions of pathological impairments frequently associated with development will be greatly appreciated by readers involved in the rehabilitation of clinical patients. In the final section, the main evidences for a contribution of the motor system to language perception and comprehension are summarized and the controversy in the interpretations of the data are discussed, leading to suggestions for original research programmes.
The co-editors were successful in convincing the main researchers in the field to contribute to the volume. The result is a timely survey of the embodied semantics theory of language, which gives the volume its conceptual unity. This theory claims that part of language comprehension is grounded in sensory and motor mechanisms. Language pertains to a system for manipulating knowledge. In that perspective, words are tools for retrieving, using and communicating our own knowledge about aspects of the external world: our conceptual knowledge about concrete objects or abstract concepts, and our procedural knowledge about physical forces and interactions during reaching goals. There are still other unexplored types of knowledge as well, such as affective knowledge about emotions, feelings and states of mind in general, as experienced by ourselves and shared with others. This opens avenues for future research.
Marc Jeannerod