The Psychology of Communication


11.3 Biological Basis Of Speech

Noam Chomsky argues that children learn to speak so effortlessly because they are born with a language acquisition device (LAD). The physiological structure corresponding to this hypothetical construct has not been identified. However the empirical evidence for such a device is so overwhelming that there must be some structure (or, more likely, some system of structures) which corresponds to this concept. Major candidates are two areas of the brain which have long been identified with speech - Broca's area and Wernicke's area, named in honor, respectively, of Paul Broca and Karl Wernicke who located those areas. They located them by finding consistent, distinctive speech aberrations in patients with damage to their respective areas. Broca found that his patients exhibited slow, labored, poorly articulated speech. Wernicke found that his patients exhibited fluid speech but it did not make any sense. Considerable research has identified Broca's area with syntactics (that is, the internal structure of language) and Wernicke's area with semantics {that is, with the external link of language to meaning) [ZURIF]. Those two areas are linked by a structure called the arcuate fasciculus and the cutting of this structure produces predictable linguistic disorders. Patients are unable to repeat what is said to them - incoming words to the Wernicke area cannot be passed on to the Broca area to be articulated. This whole system of structures is located in the temporal lobe on the left hemisphere of the brain (see Figure 11-2).

Maps of the brain showing the location of those various modules are superficially similar to the maps created by phrenologists (see Figure 11-3). People working in this domain are whimsically called the New Phrenologists. However, their new maps are dramatically different from those old maps. Phrenologists arbitrarily placed language below the eye, without any empirical justification for this quaint location; whereas New Phrenologists place language in the temporal lobe of the left hemisphere of the cerebral cortex because damage to this area result in deficiencies in language. Phrenologists based their placement of functions on reading bumps on the skull which have no logical relationship to any bumps in the brain below; whereas New Phrenologists directly explore the relationship between the functions and structures in the brain below.

Phrenologists had no theoretical framework to tie together their set of categories; whereas the New Phrenologists are guided by the theory of evolution. It is no surprise then that there is an area devoted to such a precise function as recognition of faces. Social animals need to know who's friend and who's foe. It is no surprise, in reading a newspaper this morning, to find that trust is related to the secretion of a particular chemical - the oxytocin hormone is the biological basis of trust [FREEZE]. Social animals need to trust one another. It is no surprise on reading my newspaper ANY day to find that it is full of gossip. Social animals need gossip in order to get rid of members of the group who are not trustworthy. Thus evolutionary psychology provides a framework for understanding which modules can be expected to be found in the brain.

Since the first generation of media Memory and Speech comes to us compliments of the process of biological evolution, they must be represented somewhere in the nervous system. However, the second, third, and fourth generations come to us compliments of cultural evolution. Though the content of what we acquire from our culture must be somehow represented in the nervous system, there is no reason to assume that the tools for storing and transmitting this content have any biological basis.

That is perhaps why the biological basis of dyslexia was not considered, and thus discovered, until recently. One version of dyslexia is caused by a missing link between Broca's area and Wernicke's area and thus the dyslexic can't understand and articulate language at the same time. That is why William Calvin was so surprised when he found that his father could no longer read as a result of a stroke [CALVIN]. Surely the stroke had not damaged a Read Centre as strokes had damaged the Speech Centers of the patients of Broca and Wernicke? There is indeed not a Read Centre as such. However, since writing and reading in the second generation of media piggybacks on speaking and listening of the first generation, those activities require an intact speech centre - plus links to the visual cortex for reading and to the motor cortex for writing (see Figure 11-4). The stroke suffered by the father of William Calvin had severed that link with the visual cortex. The angular gyrus serves as a link between visual word recognition and the rest of the language system.

In Section 10.3, we considered the argument that we are Natural-Born Cyborgs [CLARK]. Andy Clark suggests that the various media tools which we master are represented in our brains. Those young people who have been raised on video- and computer-based media are biologically different from those of us raised on speaking and reading. Recent evidence that the frontal lobes are not fully formed until after adolescence lends credence to this theory. Our brains are plastic enough to accommodate those various generations of media. Thus, we acquire the extrasomatic tools of the second, third, and fourth generations of media from our culture but they become part of the system into which subsequent content is assimilated. We learn to read and then we read to learn. Do we have essentially the same brain as our hunter-gatherer ancestors with extensions or do we have different brains because those extensions are assimilated? Do our children have different brains from us because they are assimilating different extensions?