As the brain matures, specialization of specific neurological structures takes place, and this allows language to develop (Kuhl, 2010; Kuhl & Rivera-Gaxiola, 2008). Where, then, are the language centres of the brain?

In early infancy, language processing is distributed across many areas of the brain. But language processing gradually becomes more and more concentrated in two areas, Broca’s area and Wernicke’s area, sometimes referred to as the language centres of the brain. As the brain matures, these areas become increasingly specialized for language, so much so that damage to them results in a serious condition called aphasia, difficulty in producing or comprehending language.

Broca’s area is located in the left frontal cortex and is involved in the production of the sequential patterns in vocal and sign languages (see FIGURE 9.3). As you saw in the Psychology: Evolution of a Science chapter, Broca’s area is named after French physician Paul Broca, who first reported on speech problems resulting from damage to a specific area of the left frontal cortex (Broca, 1861, 1863). Individuals with this damage, resulting in Broca’s aphasia, understand language relatively well, although they have increasing comprehension difficulty as grammatical structures get more complex.

But their real struggle is with speech production. Typically, they speak in short, staccato phrases that consist mostly of content morphemes (e.g., cat, dog). Function morphemes (e.g., and, but) are usually missing and grammatical structure is impaired. A person with the condition might say something like “Ah, Monday, uh, Casey park. Two, uh, friends, and, uh, 30 minutes.”

Wernicke’s area, located in the left temporal cortex, is involved in language comprehension (whether spoken or signed). German neurologist Carl Wernicke first described the area that bears his name after observing speech difficulty in patients who had sustained damage to the left posterior temporal cortex (Wernicke, 1874). Individuals with Wernicke’s aphasia differ from those with Broca’s aphasia in two ways: They can produce grammatical speech, but it tends to be meaningless, and they have considerable difficulty comprehending language. A person suffering from Wernicke’s aphasia might say something like, “Feel very well. In other words, I used to be able to work cigarettes. I do not know how. Things I could not hear from are here.”

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In normal language processing, Wernicke’s area is highly active when we make judgments about word meaning, and damage to this area impairs comprehension of spoken and signed language, although the ability to identify nonlanguage sounds is unimpaired. For example, Japanese can be written using symbols that, like the English alphabet, represent speech sounds, or by using pictographs that, like Chinese pictographs, represent ideas. Japanese persons who suffer from Wernicke’s aphasia encounter difficulties in writing and understanding the symbols that represent speech sounds but not pictographs (Sasanuma, 1975).

As important as Broca’s and Wernicke’s areas are for language, they are not the entire story. Three kinds of evidence indicate that the right cerebral hemisphere also contributes to language processing, especially to language comprehension (Jung-Beeman, 2005). First, when words are presented to the right hemisphere of healthy participants using divided visual field techniques (see the Neuroscience chapter), the right hemisphere shows some capacity for processing meaning. Second, individuals with damage to the right hemisphere sometimes have subtle problems with language comprehension. Third, and most directly related to language development, some children who have had their entire left hemispheres removed during adolescence as a treatment for epilepsy can recover many of their language abilities.

Around the world, most people grow up speaking more than one language. Bilingualism (or multilingualism) is the norm, rather than the exception. In Canada, over 200 languages are represented, and more than a third of the population speaks more than one language fluently (Statistics Canada, 2012a). (See the Other Voices box for an opinion on the state of bilingualism in Canada.) What is the effect of such rich language development on the brain?

Early studies of bilingual children seemed to suggest that bilingualism slows or interferes with normal cognitive development. When compared with monolingual children, bilingual children performed more slowly when processing language, and their IQ scores were lower. A re-examination of these studies, however, revealed several crucial flaws. First, the tests were given in English even when that was not the child’s primary language. Second, the bilingual participants were often first- or second-generation immigrants whose parents were not proficient in English. Finally, the bilingual children came from lower socioeconomic backgrounds than the monolingual children (Andrews, 1982).

Later studies controlled for these factors, revealing a very different picture of bilingual children’s cognitive skills. The available evidence concerning language acquisition indicates that bilingual and monolingual children do not differ significantly in the course and rate of many aspects of their language development (Nicoladis & Genesee, 1997). In fact, middle-class children who are fluent in two languages have been found to score higher than monolingual children on several measures of cognitive functioning, including executive control capacities such as the ability to prioritize information and flexibly focus attention (Bialystok, 1999, 2009; Bialystok, Craik, & Luk, 2012). The idea here is that bilingual individuals benefit from exerting executive control in their daily lives when they attempt to suppress the language that they do not want to use. Recent evidence indicates that bilingualism also has benefits much later in life: Bilingual individuals tend to have a later onset of Alzheimer’s disease than monolingual individuals, perhaps reflecting that during their lives they have built up a greater amount of back-up cognitive ability or “cognitive reserve” (Schweizer et al., 2012). These findings are consistent with research showing that learning a second language produces lasting changes in the brain (Mechelli et al., 2004; Stein et al., 2009). For example, the grey matter in a part of the left parietal lobe that is involved in language is denser in bilingual than in monolingual individuals, and the increased density is most pronounced in those who are most proficient in using their second language (see FIGURE 9.4) (Mechelli et al., 2004).

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Some studies have revealed disadvantages, however. Bilingual children tend to have a smaller vocabulary in each language than their monolingual peers (Portocarrero, Burright, & Donovick, 2007); they also process language more slowly than monolingual children and can sometimes take longer to formulate sentences (Bialystok, 2009; Taylor & Lambert, 1990). Thus, learning a second language produces a number of benefits along with some costs.

The human vocal tract and the extremely nimble human hand are better suited to human language than are the throats and paws of other species. Nonetheless, attempts have been made to teach nonhuman animals, particularly apes, to communicate using human language.

Early attempts to teach apes to speak failed dismally because their vocal tracts cannot accommodate the sounds used in human languages (Hayes & Hayes, 1951). Later attempts to teach apes human language have met with more success, including teaching them to use American Sign Language and computer-monitored keyboards that display geometric symbols that represent words. Allen and Beatrix Gardner were the first to use ASL with apes (Gardner & Gardner, 1969). The Gardners worked with a young female chimpanzee named Washoe as though she were a deaf child, signing to her regularly, rewarding her correct efforts at signing, and assisting her acquisition of signs by manipulating her hands in a process referred to as molding. In 4 years, Washoe learned approximately 160 words and could construct simple sentences, such as “More fruit.” She also formed novel word constructions such as “water bird” for “duck.” After a fight with a rhesus monkey, she signed, “Dirty monkey!” This constituted a creative use of the term because she had only been taught the use of dirty to refer to soiled objects.

Other chimpanzees were immersed in ASL in a similar fashion, and Washoe and her companions were soon signing to each other, creating a learning environment conducive to language acquisition. One of Washoe’s cohorts, a chimpanzee named Lucy, learned to sign “drink fruit” for watermelon. When Washoe’s second infant died, her caretakers arranged for her to adopt an infant chimpanzee named Loulis.

In a few months, young Loulis, who was not exposed to human signers, learned 68 signs simply by watching Washoe communicate with the other chimpanzees. People who have observed these interactions and are themselves fluent in ASL report little difficulty in following the conversations (Fouts & Bodamer, 1987). One such observer, a New York Times reporter who spent some time with Washoe, reported, “Suddenly I realized I was conversing with a member of another species in my native tongue.”

Other researchers have taught bonobo chimpanzees to communicate using a geometric keyboard system (Savage-Rumbaugh, Shanker, & Taylor, 1998). Their star pupil, Kanzi, learned the keyboard system by watching researchers try to teach his mother. Like Loulis, young Kanzi picked up the language relatively easily (his mother never did learn the system), suggesting that like humans, birds, and other species, apes experience a critical period for acquiring communicative systems.

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Kanzi has learned hundreds of words and has combined them to form thousands of word combinations. Also like human children, his passive mastery of language appears to exceed his ability to produce language. In one study, researchers tested 9-year-old Kanzi’s understanding of 660 spoken sentences. The grammatically complex sentences asked him to perform simple actions, such as “Go get the balloon that’s in the microwave” and “Pour the Perrier into the Coke.” Some sentences were also potentially misleading, such as “Get the pine needles that are in the refrigerator,” when there were pine needles in clear view on the floor. Impressively, Kanzi correctly carried out 72 percent of the 660 requests (Savage-Rumbaugh & Lewin, 1996).

These results indicate that apes can acquire sizable vocabularies, string words together to form short sentences, and process sentences that are grammatically complex. Their skills are especially impressive because human language is hardly their normal means of communication. Research with apes also suggests that the neurological “wiring” that allows us to learn language overlaps to some degree with theirs (and perhaps with other species’).

Equally informative are the limitations apes exhibit when learning, comprehending, and using human language. The first limitation is the size of the vocabularies they acquire. As mentioned, Washoe’s and Kanzi’s vocabularies number in the hundreds, but an average 4-year-old human child has a vocabulary of approximately 10 000 words. The second limitation is the type of words they can master, primarily names for concrete objects and simple actions. Apes (and several other species) have the ability to map arbitrary sounds or symbols onto objects and actions, but learning, say, the meaning of the word economics would be difficult for Washoe or Kanzi. In other words, apes can learn signs for concepts they understand, but their conceptual repertoire is smaller and simpler than that of humans.

The third and perhaps most important limitation is the complexity of grammar that apes can use and comprehend. Apes can string signs together, but their constructions rarely exceed three or four words, and when they do, they are rarely grammatical. Comparing the grammatical structures produced by apes with those produced by human children highlights the complexity of human language as well as the ease and speed with which we generate and comprehend it.

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