Online research in philosophy

A new view of the functional role of the left anterior cortex in language use is proposed. The experimental record indicates that most human linguistic abilities are not localized in this region. In particular, most of syntax (long thought to be there) is not located in Broca's area and its vicinity (operculum, insula, and subjacent white matter). This cerebral region, implicated in Broca's aphasia, does have a role in syntactic processing, but a highly specific one: It is the neural home to receptive mechanisms involved in the computation of the relation between transformationally moved phrasal constituents and their extraction sites (in line with the Trace-Deletion Hypothesis). It is also involved in the construction of higher parts of the syntactic tree in speech production. By contrast, basic combinatorial capacities necessary for language processing – for example, structure-building operations, lexical insertion – are not supported by the neural tissue of this cerebral region, nor is lexical or combinatorial semantics. The dense body of empirical evidence supporting this restrictive view comes mainly from several angles on lesion studies of syntax in agrammatic Broca's aphasia. Five empirical arguments are presented: experiments in sentence comprehension, cross-linguistic considerations (where aphasia findings from several language types are pooled and scrutinized comparatively), grammaticality and plausibility judgments, real-time processing of complex sentences, and rehabilitation. Also discussed are recent results from functional neuroimaging and from structured observations on speech production of Broca's aphasics. Syntactic abilities are nonetheless distinct from other cognitive skills and are represented entirely and exclusively in the left cerebral hemisphere. Although more widespread in the left hemisphere than previously thought, they are clearly distinct from other human combinatorial and intellectual abilities. The neurological record (based on functional imaging, split-brain and right-hemisphere-damaged patients, as well as patients suffering from a breakdown of mathematical skills) indicates that language is a distinct, modularly organized neurological entity. Combinatorial aspects of the language faculty reside in the human left cerebral hemisphere, but only the transformational component (or algorithms that implement it in use) is located in and around Broca's area. Key Words: agrammatism; aphasia; Broca's area; cerebral localization; dyscalculia; functional neuroanatomy; grammatical transformation; modularity; neuroimaging; syntax; trace deletion.

The interaction between brain and language has been investigated by a vast amount of research and different approaches, which however do not offer a comprehensive and unified theoretical framework to analyze how brain functioning performs the mental processes we use in producing language and in understanding speech. This Special Issue addresses the need to develop such a general theoretical framework, by fostering an interaction among the various scientific disciplines and methodologies, which centres on investigating the functional architecture of brain, mind and language, and is articulated along the following main dimensions of research: (a) Language as a regulatory contour of brain and mental processes; (b) Language as a unique human phenomenon; (c) Language as a governor of human behaviour and brain operations; (d) Language as an organizational factor of ontogenesis of mentation and behaviour.

Toolmaking requires motor skills that in turn require handedness, so that there is no competition between the two sides of the brain. Thus, handedness is not necessarily linked to vocalization but to the origin of causal beliefs required for making complex tools. Language may have evolved from these processes.

I do not disagree with the argument that human-population right-handedness may in some way be a consequence of the population-level left-lateralization of language. But I suggest that the human functional lateralization is not dependent on the structural left-right brain asymmetries to which Corballis refers.

Charmed by Corballis's presentation, we challenge the use of mirror neurons as a supporting platform for the gestural theory of language, the link between vocalization and cerebral specialization, and the relationship between gesture and language as two separate albeit coupled systems of communication. We revive an alternative explanation of lateralization of language and handedness.

While language is presumably unique to humans, there are possible pre-linguistic features that developed in the course of human evolution which predate features of language, and might have even been essential for its evolution. A number of such possible preadaptations for human language have been discussed, like the permanent lowering of the larynx, the ability to control one’s breath, or the inclination of humans to imitate. In this paper I would like to point out another candidate for a preadaptation, namely the functional differentiation of the hands and the way in which they cooperate in manual actions.

Many commentators have raised issues concerning the idea that language evolved from manual gestures. I deal with these first, reiterating the points that speech is very different from animal vocal calls, and that cortical control over manual action provided the best platform for the evolution of intentional communication and language. I then deal with commentaries on the origins of handedness. The critical questions are whether there is indeed an evolutionary coupling between handedness and lateralized control of speech, and if there is, whether a prior lateralization of vocal control provided the nudge that gave most of us left-sided speech and right-handedness.

I would like to stress that early development repeats the evolution of the species. Hence, to understand the origins of functional brain asymmetry and the underlying mechanisms involved in handedness, we have to seek information not only from what we know about human evolution, but also from how an early hand preference develops in our own species.

The strong predominance of right-handedness appears to be a uniquely human characteristic, whereas the left-cerebral dominance for vocalization occurs in many species, including frogs, birds, and mammals. Right-handedness may have arisen because of an association between manual gestures and vocalization in the evolution of language. I argue that language evolved from manual gestures, gradually incorporating vocal elements. The transition may be traced through changes in the function of Broca's area. Its homologue in monkeys has nothing to do with vocal control, but contains the so-called “mirror neurons,” the code for both the production of manual reaching movements and the perception of the same movements performed by others. This system is bilateral in monkeys, but predominantly left-hemispheric in humans, and in humans is involved with vocalization as well as manual actions. There is evidence that Broca's area is enlarged on the left side in Homo habilis, suggesting that a link between gesture and vocalization may go back at least two million years, although other evidence suggests that speech may not have become fully autonomous until Homo sapiens appeared some 170,000 years ago, or perhaps even later. The removal of manual gesture as a necessary component of language may explain the rapid advance of technology, allowing late migrations of Homo sapiens from Africa to replace all other hominids in other parts of the world, including the Neanderthals in Europe and Homo erectus in Asia. Nevertheless, the long association of vocalization with manual gesture left us a legacy of right-handedness. Key Words: cerebral dominance; gestures; handedness; hominids; language evolution; primates; speech; vocalization.

The target article by Corballis presents an interesting and novel theoretical perspective on the evolution of language, speech, and handedness. There are two specific aspects of the article that will be addressed in this commentary: (a) the link between Broca's area and gestural communication in chimpanzees, and (b) the issue of population-level handedness in great apes, notably chimpanzees.