A critical look at the embodied cognition hypothesis and a new proposal for grounding conceptual content
Introduction
The role of sensory and motor processes in conceptual processing is a central topic of study in cognitive science. A broad hypothesis space is currently available regarding the potential role(s) of the sensory and motor systems in conceptual processing. At one end of the hypothesis space is the view that conceptual content is reductively constituted by information that is represented within the sensory and motor systems – the embodied cognition hypothesis compared to the disembodied cognition hypothesis. According to the embodied cognition hypothesis, ‘understanding’ is sensory and motor simulation. At the other end of the hypothesis space is the view that concepts are not constituted by information that is represented within the sensory and motor systems – the (so-called) disembodied cognition hypothesis. According to the disembodied cognition hypothesis, conceptual representations are ‘symbolic’ and ‘abstract’, and as such, qualitatively distinct and entirely separated from sensory and motor information.
Methodologies that permit the imaging of the normally functioning human brain have generated a large amount of data showing that sensory and motor activation accompanies conceptual processing. Such observations have been interpreted as providing support for the embodied cognition hypothesis compared to the disembodied cognition hypothesis. Other evidence cited in support of the embodied cognition hypothesis comes from behavioral studies of language-induced motor resonance. On the other hand, cognitive neuropsychological studies of patients with sensory and/or motor impairments demonstrate that such impairments do not necessarily give rise to conceptual deficits.
Here we show that the currently available evidence that has been used to argue for or against the embodied cognition hypothesis is inadequate to resolve the issue of how concepts are represented in the brain. This is because the way in which the hypothesis space has been set up severely limits the utility of such evidence to speak to the positive role(s) that the sensory and motor systems may have in representing concepts.
The structure of the argument in this article is in two parts. In the first part, we show that a disembodied theory of cognition can account for the evidence that has been cited in favor of the embodied cognition hypothesis. The purpose of the argument in this first part of the article is to show that the embodied cognition hypothesis is without empirical support relative to other theories, because the available evidence is consistent with a strict representational distinction between ‘abstract’ and ‘symbolic’ conceptual content and sensory and motor representations. In the second part of the article, we sketch an account of concepts that occupies a middle ground between the embodied and disembodied cognition hypotheses.
The embodied and disembodied cognition hypotheses propose different roles for sensory and motor information in conceptual representation. According to the disembodied view of concept representation, the output of conceptual processing must, at some level of processing be packaged into a format that can be ‘read’ by the neural systems that enervate the body. For instance, consider the situation in which a person is presented with a hammer and asked to demonstrate its use. From the visual input of seeing the hammer, the concept HAMMER would be retrieved. That concept, on the disembodied cognition hypothesis, would be an ‘abstract’ and ‘symbolic’ representation that would not be constituted by information in the sensory and motor systems. This representation, once retrieved, would have to contact or ‘index’ the relevant information in the motor system about how to manipulate the object. In this sense, there would be interfaces between ‘abstract’ and ‘symbolic’ conceptual computations and the sensory and motor systems.
According to the embodied cognition hypothesis, conceptual processing already is sensory and motor processing. For instance, in the example of the person demonstrating the use of the hammer, the process of retrieving the concept HAMMER would itself be constituted by the retrieval of (sensory and motor) information about how to use hammers (i.e., swinging the arm, grasping the object, coordinating the visuo-motor relationships between the nail and the head of the hammer, etc.). On the extreme form of the embodied cognition hypothesis, there would be no ‘interface’ between a ‘concept’ and the sensory/motor system. The process of ‘concept retrieval’ would already be the process of retrieving the sensory and motor information that would directly mediate hammer usage. This does not mean that an embodied cognition hypothesis would not face its own challenges about specifying the nature of the interface between perceptual and motor systems (Hommel et al., 2001).
Concepts of concrete objects (e.g., HAMMER) could plausibly include, in a constitutive way, sensory and motor information. But consider concepts such as JUSTICE, ENTROPY, BEAUTY or PATIENCE. For abstract concepts there is no sensory or motor information that could correspond in any reliable or direct way to their ‘meaning’. The possible scope of the embodied cognition framework is thus sharply limited up front; at best, it is a partial theory of concepts since it would be silent about the great majority of the concepts that we have. Given that an embodied theory of cognition would have to admit ‘disembodied’ cognitive processes in order to account for the representation of abstract concepts, why have a special theory just for concepts of concrete objects and actions?
Section snippets
The embodied cognition hypothesis: Is there a ghost in the motor system?
The data that have been cited in support of the embodied cognition hypothesis can be organized into four types: (I) ‘direct’ demonstrations (i.e., brain based measures) that the motor system is activated during perceptual and conceptual processing; (II) behavioral demonstrations that activation in the motor system spreads to conceptual and perceptual levels of processing; (III) demonstrations of motor and/or sensory activation induced by sentence comprehension; and (IV) impaired lexical
The disembodied cognition hypothesis: Is motor system activation during conceptual processing merely Pavlovian?
There are other findings from neuropsychology, and in particular, Apraxia, that provide some leverage on the issue of whether or not important aspects of some concepts are embodied. Apraxia is an impairment for using objects that cannot be explained by basic sensory or motor impairments. There are now a number of studies, from different research groups, using different materials and scoring methods, that converge on two empirical facts: patients can be impaired for using objects despite being
Interim summary
The embodied cognition hypothesis cannot be true as a general theory of human cognition (think of representations/concepts such as ‘300,012,’ incredulous, astute, theory, embodied, false and on and on). Experiments are not required to demonstrate that the scope of the embodied cognition hypothesis is sharply limited up front. Nevertheless, the issue of whether the embodied cognition hypothesis offers a cogent and empirically valid account of the representation of concrete objects and actions is
Grounding by interaction
Consider the hypothetical apraxic patient with whom one might have a conversation about hammers. The patient might be able to recount the history of the hammer as an invention, the materials of which the first hammer was made, or what hammers typically weigh. The patient may even look at a hammer and name it without apparent difficulty. But when presented with a hammer, the patient is profoundly impaired at demonstrating how the object is physically manipulated to accomplish its function. This
Conclusion
It is one of the most important insights of cognitive neuroscience that processes are activated that ‘go beyond’ the ‘logical’ requirements of the task. Those findings have provoked major revisions to classical views about how the mind works. We have suggested that while the spirit of those revisions is welcome, the specific conclusions that have been reached are not supported, relative to other viable theories, by the empirical evidence. Recognition of this point is, we believe, important in
Acknowledgements
Preparation of this manuscript was supported by an NSF Graduate Research Grant to B.Z.M. and by NIH Grant DC04542 to A.C. The authors are grateful to Jorge Almeida, Stefano Anzellotti, Jessica Cantlon, Arthur Glenberg, Naomi Zack, and two anonymous reviewers for their comments on an earlier draft.
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