PSY 340 Brain and Behavior
Class 35: Evolution and Physiology of Language
The Evolution and Physiology of Language
A. Human language is unique because of it productivity, that is, its ability to produce new signals to represent new ideas.
Consider how the invention of the Internet has forced us to create a whole new set of symbols and ways of conveying meanings.
B. Nonhuman Precursors to Language
1. Common chimpanzees can not learn to talk, but can learn some language skills using American Sign Language or other visual systems. Their use of language-related symbols differ from human language in many ways:
a. The chimpanzees seldom used the symbols in new original combinations (they are not productive).
b. The chimpanzees used their symbols almost always to make a request, only rarely to describe.
c. The chimpanzees produced requests far better than they seem to understand anyone else's request.
d. They do show a moderate degree of understanding of what is communicated to them, e.g., "who?" questions answered by names; "what?" questions answered by things; and "where?" questions answered by places.
2. Bonobos (Pan paniscus) , a "cousin" of the common chimpanzee, when given language training uses symbols in several ways that more resemble humans than common chimpanzees:
a. They understood more information than they produce.
b. They use symbols to name and describe objects even when they are not requesting them.
c. They request items that they do not see.
d. They occasionally use the symbols to describe past events.
e. They frequently make original, creative requests.
3. The reason for the better language skills in the bonobos than in chimps is unknown.
4. Nonprimates: Alex, African gray parrot (1976-2007)Trained by Dr. Irene Pepperberg (originally U Arizona, now affiliated with Brandeis U-Harvard-visiting @ MIT Media Lab) from age 1. Alex died unexpectedly Sept 6, 2007 of heart disease.
Alex had relatively extensive language ability with specific objects & concepts:
- Alex "could identify fifty different objects and recognize quantities up to six; that he could distinguish seven colors and five shapes, and understand the concepts of "bigger", "smaller", "same", and "different," and that he was learning "over" and "under".
- Alex had a vocabulary of about 150 words, but was exceptional in that he appeared to have understanding of what he said. For example, when Alex was shown an object and was asked about its shape, color, or material, he could label it correctly. If asked the difference between two objects, he also answered that, but if there was no difference between the objects, he said “none.”" (Wikipedia, retrieved April 21, 2008)
Pepperberg offers an evolutionary explanation for intelligence (which, presumably, is the basis of language) by citing the examples of both apes and parrots who live to become 30 to 60 years old:
"Nick Humphrey suggested these ideas almost 30 years ago:... given a long-lived creature that exists in a complex socio-ecological system, that creature has likely been selected for high-level intelligence and cognition. I think those same evolutionary pressures work on parrots." ("That damned bird," 2003)
C. How Did Humans Evolve Language?
1. Is Language Just a Product of Overall Intelligence or a Specialized Adaptation? Answer: Probably a Specialized Adaptation
a. The relationship between brain and brain-to-body ratio is unclear (see chart below or click here for larger image). Human beings do not have the largest brain-to-body mass ratio: dolphins, elephants, and blue whales do. Yet these animals do no use language in ways that are parallel to human beings.
b. The evolution of language seems to require a brain mechanism called the phonological loop, that is, the ability to hear and remember something (remember that this loop is one of the elements in Baddeley's model of working memory).
Language also seems to depend upon gestures, particularly those gestures involving the face and mouth. When we listen to others in noisy settings, we pay particular attention to the face and mouth of the other speaker in order to understand what they are saying.
c. People with Normal Intelligence but Impaired Language
"KE" Family (a British family of Pakistani origin) & "CS" (an unrelated English boy with same language problem)
Presumably because of an altered dominant gene (FOXP2 ["“forkhead box P2”"] segment on chromosome 7), 16 of 30 people of normal intelligence within one family (& "CS") have severe difficulty with pronunciation, and all other aspects of language. Cases such as this suggest that genetic conditions which affect brain development can impair language without impacting other aspects of intelligence. (Itzhaki, 2003; Liegeois et al., 2003; MacAndrew, 2003).
==> Conclusion 1: General intelligence is not sufficient for language.
d. People with Intellectual Disability (Low Intelligence) but Relatively Spared Language
Williams syndrome (also known as Williams-Beuren Syndrome) = people with intellectual disability but good language skills. Also musical rhythm ability. Fascination with faces (fusiform gyrus is 2X normal).
A rare disorder (~1 in 20,000 births according to Kalat; ~1 in 8000 live births according to Haas & Reiss, 2012) in which individuals with intellectual impairments have relatively skillful use of language, but limited abilities in other regards. This disorder is caused by a deletion of several genes from chromosome 7.
Pascual-Castroviejo et al. (2004) summarized other characteristic symptoms:
- Distinctive facial appearance ("elfin-like")
- Intellectual disability (IQ < 70)
- Very socially friendly behavior
- Congenital heart problems including supravalvular aortic stenosis & pulmonary stenosis
- ADHD-like behaviorNew/Not in book:
Evelina Fedorenko (MGH/Harvard) & Rosemary Varley (UCL, UK; 2016) report that "language and thought are not the same thing" on the basis of multiple neuroimaging studies
- Patients with global aphasia (= have almost no ability to understand or produce language) can still "add/subtract, solve logic problems, thing about other person's thoughts, appreciate music, and successfully navigate their environments" (abstract)
- Neuroimaging studies show different patterns of engagement of the brain's language areas. Areas that are active when individuals attempt to understand a sentence are not active when individuals perform other "non linguistic tasks such as arithmetic, storing information in working memory, listening to music" et al. (abstract)
- Fedorenko et al (2016) conclude that "Evidence from brain imaging investigations and studies of patients with severe aphasia show that language processing relies on a set of specialized brain regions, located in the frontal and temporal lobes of the left hemisphere. These regions are not active when we engage in many forms of complex thought, including arithmetic, solving complex problems, listening to music, thinking about other people’s mental states, or navigating in the world. Furthermore, all these nonlinguistic abilities further appear to remain intact following damage to the language system, suggesting that linguistic representations are not critical for much of human thought" (p. 12)
Conclusion 2: Language does not appear to be a by-product of general intelligence or general intellectual activity
2. Is Language a Speciaiization of the Brain?
a. First proposed by MIT linguistics scholar, Noam Chomsky and more recently championed by Steven Pinker at Harvard, an alternate view of the evolution of language is that language evolved as an extra brain module, called a language acquisition device (LAD). This idea is supported by the fact that children learn language with amazing ease and that children learn language despite the fact they do not hear enough examples to learn the grammatical structure of language (this is called the poverty of the stimulus argument).
b. A Sensitive Period for Language Learning
Argument: Language has a critical period, because if you don't learn language when you are young, you will forever be language disadvantaged.
- Late vs. Early Second Language Learning
- Adults better at learning vocabulary of new language, but children better at learning grammar & pronunciation, for example, adult Chinese speakers learning English have major trouble with use of the articles "a" and "the" (Chinese has no articles). This is similar to findings with speakers of Slavic languages such as Russian which also do not have articles.
- Deaf children: Early learning of sign language = better use of sign language
- NOT IN BOOK: See, also, the experience of what are called "feral children" who "have spent much of their formative years in the wild, without any contact with other humans for a significant period of their lives" (Woodpigeon, 2000). In the few confirmed cases, these children experience significant social handicap and learn almost no language (not in book)
Conclusion 3: There is no language module which automatically causes a person to learn to speak. Rather the predisposing neural structures require social experience in the company of other people in order to develop most appropriately.
3. Language and the "Social Brain" Hypothesis (not in textbook)
a. Without rejecting the LAD theory above, we should note that language always arises within a social context and depends upon social interaction for its development (a corollary of the "critical period" observation). A purely biological explanation for the emergence of language is unlikely. Vasanta (2005) states this caution by claiming:
"...syntax-centered definitions of language knowledge [such as the LAD theory] completely ignore certain crucial aspects of language learning and use, namely, that language is embedded in a social context; that the role of environmental triggering as a learning mechanism is grossly underestimated; that a considerable extent of visuo-spatial information accompanies speech in day-to-day communication; that the developmental process itself lies at the heart of knowledge acquisition; and that there is a tremendous variation in the orthographic systems associated with different languages." (Abstract)
b. Contrary to the theory of the evolution of general intelligence, Robin Dunbar (U Liverpool, UK) and others propose that language developed as a way of helping organize larger and larger social grouping. This "social brain" hypothesis rests upon a variety of observations including two advantages conveyed by language:
- the ability to categorize individuals into distinct types (e.g., doctor, sheriff, chief)
- the ability to instruct other individuals about how they should respond "toward specific types of individuals within society" (Dunban, 1993)
Essentially, language permits societies of much larger size than would be possible otherwise. Such groups, e.g., bands, tribes, etc., have an survival advantage vis-a-vis those who do not have language.
D. Brain Damage and Language
1. Aphasia = Severe language impairment
2a. Broca's Area: Small part of the frontal lobe of the left cerebral cortex that when damaged leads to impairments in language production.
2b. Wernicke's Area
- Traditionally, Wernicke's Area has been located on the superior temporal cortex posterior to (behind) the Primary Auditory Cortex. Indeed, in our textbook, that is where the area is shown in a diagram. Damage to that area has usually been seen to lead to impairments in language comprehension.
- However, in the last decade with the coming of neuroimaging techniques to examine the brains of living persons with language impairments, a new understanding of what anatomical areas may be involved in this region has emerged. DeWitt & Rauchecker (2012) proposed that there is a region anterior to (in front of) the Primary Auditory Cortex that is involved in the recognition of speech sounds/phononlogical processing. And, going even further, Binder (2017) argues that it is damage to this anterior/medial area that is the cause of language comprehension loss.
- The traditional posterior superior temporal cortex that has been labeled "Wernicke's Area" seems to be primarily involved in “retrieval of phonological forms (mental representations of phoneme sequences), which are used for speech output and short-term memory tasks. Focal damage to this region produces phonemic paraphasia without impairing word comprehension” (Binder, 2017, Abstract, boldface & italics added). That term “phonemic paraphrasia” means the substitution of a word with a nonword that preserves at least half of the segments and/or number of syllables of the intended word, e.g., instead of saying “instructional resources” the person might say “instudinal desources”
3. Broca's aphasia (or nonfluent aphasia): A language impairment whose most prominent symptom is a deficit in language production. Caused by damage to Broca' area and surrounding areas.
a. Patients suffering from Broca's aphasia often speak meaningfully, but omit pronouns, prepositions, conjunctions, and qualifiers from their own speech; they also have trouble understanding these same kinds of words. Other more seriously impaired individuals have significant difficulty forming the words themselves and will slur or otherwise produce difficult to understand language.
Broca's aphasia - Sarah Scott - teenage stroke
4. Wernicke's aphasia or fluent aphasia involves a difficulty in comprehending the verbal and written communications of others. Although patients can still speak smoothly, their speech content is often nonsensical. They also have anomia (difficulty recalling the names of objects). Note above the damage causing this may have nothing to do with "Wernicke's Area"
Wernicke's aphasia - Retired dentist
5. Language requires the activation of many different areas other than the frontal cortex (Broca's area and surrounding regions) and the temporal cortex.
1. Dyslexia: Inability to read or significant difficulty with reading despite adequate vision and intelligence. Many kinds of dyslexia exist with different underlying causes. This is also a topic which has caused a great deal of argumentation and struggle among researchers, teachers, parents, and students for many decades.
- There is NO link between intelligence and dyslexia. Indeed there are many quite intelligent and successful people with dyslexia.
- Dyslexia is a condition that one does not "outgrow"
- Forms of dyslexia from mild to severe affects between 10% and 20% of the population
- Males and females show roughly equal percentages of dyslexic symptoms (dyslexia is NOT a "boy" problem).
- There appears to be a strong genetic component in dyslexia with the children of parents with dyslexia much more likely to develop the disorder.
2. D'Mello & Gabrieli (2018) summarize the key findings from fMRI and other studies. These suggest that individuals with dyslexia show....
- Underactivation in Verbal Word Form Area (in the fusiform gyrus of the left occipital-temporal cortex) "in response to world or work-like materials...[Further] reduced activation in this region is a persistent difference across both children and adults with dyslexia" (p. 801)
- "In children and adults with dyslexia, the left temporo-parietal cortex is consistently underactivated during phonological [sound] processing tasks consistent with the proposed role of this region in grapheme-to-phoneme mapping (mapping printed letters to individual sounds)" (pp. 801-802)
- "In contrast...studies often find increased engagement of the left inferior frontal region in dyslexia. Increased activation in this region could be associated with compensatory processes that may rely on covert or subvocal reading or an increased effort. Whereas typical readers show age-dependent decreases in activation in this region, readers with dyslexia show hyperactivation across ages" (p. 802)
3. As a rule, a dyslexic person is more likely to have a bilaterally symmetrical cerebral cortex (i.e., the planum temporale and other structures are the same size on the left and right hemisphere).
- Temple and her colleagues (2003) found that, after behavioral intervention to teach dyslexic children better reading strategies, there was increased activation in the left temporo-parietal cortex that had previously been underactive.
4. Other problems observed in persons with dyslexia (note that not all individuals with dyslexia shows all these problems):
a. Dysphonic dyslexia (dys = poor; phonos = sound) = difficulty sounding out printed words
b. Dyseidetic dyslexia (dys = poor; eidos = image) = difficulty recognizing words as a whole (though can sound them out)
c. Poor auditory memory: difficulty in remembering the sequence of sounds. Suggests that there may be a problem involving the connection between the visual and auditory processing areas of the brain.
c. Dyslexia is a function of attentional differences in which there are problems attending to information directly in front of the reader, that is, dyslexic readers have a fixation point 5 to 10 degrees to the right or left of the word in front of them. Check out the image on the right side.
Try to keep your eye fixated on the dot in the middle while you try to read the letters on either the right or the left of the dot. Individuals with dyslexia often find it easier to do so than those who do not have dyslexia.
Binder, J. R. (2017). Current controversies on Wernicke’s Area and its role in language. Current Neurology and Neuroscience Reports, 17, 58. https://doi.org/10.1007/s11910-017-0764-8
DeWitt, I., & Rauschecker, J. P. (2012) Phoneme and word recognition in the auditory ventral stream. PNAS. https://doi.org/10.1073/pnas.1113427109
D'Mello, A. M., & Gabrieli, J. D. E. (2019). Cognitive neuroscience of dyslexia. Language, Speech, and Hearing Services in Schools, 49, 798-809. doi: 10.1044/2018_LSHSS-DYSLC-18-0020
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This page was first posted April 24, 2005