Chapter 12 Summary

The human vocal tract and its controlling neural apparatus have become highly specialized over evolutionary time, allowing this system to produce approximately 200 distinct speech sounds (phones), which produce corresponding auditory percepts (phonemes). A few tens of these speech sounds are used in any given language to produce the syllables, words, phrases, sentences, and ultimately the narratives that humans use to communicate verbal information.
Language must be learned in early life, and if such experience does not occur, then a person’s linguistic ability is severely and permanently limited. Nonetheless, an infant’s brain, like the vocally relevant brain regions of some other species, is already prepared to incorporate the speech information that the infant hears.
Virtually all researchers studying the neural bases of language are now agreed that most of the semantic, grammatical, and syntactical processing of language comprehension and expression resides in a number of interconnected regions of the left frontal, temporal, and parietal cortices in the majority of humans. Nevertheless, there is a great deal of individual variation, including variation in the degree of lateralization and the location of the relevant areas.
Most researchers also agree that the corresponding cortical regions in the right hemisphere contribute importantly to language by adding the emotional coloring evident in speech prosody, and presumably by interpreting this and other nonverbal aspects of language. The right hemisphere also has the rudiments of the processing abilities that exist in the left hemisphere, as evidenced by split-brain patients, again with wide variation among individuals.
Electrophysiological recording, brain imaging, and other techniques have gradually made clear that the language-processing areas initially identified by clinical-pathological correlations are components of a widely distributed set of brain regions that allow humans to communicate effectively by means of tokens that can be attached ad infinitum to objects, concepts, and feelings deemed important, and that these same areas are involved in other functions.
Comparison of the neural substrates of sign language in congenitally deaf individuals shows further that the cortical representation of language is independent of the means of its expression and perception (spoken and heard versus gestured and seen). Thus, the neural bases of language represent a system for symbolic processing that transcends verbal expression as such.
Although phenomenally well developed in humans compared to other animals, language has many basic similarities with systems of social communication in other species, which appear to entail the same general scheme of constructing acquired neural associations within a framework of dedicated brain circuitry that has already been put in place by inherited developmental programs.