Chapter 11 - Language.docx

*Jane Wagner* CHAPTER Language ======== - How does the brain derive meaning from language? - Do the processes that enable speech comprehension differ from those that enable reading comprehension? - How does the brain produce spoken, signed, and written output to communicate meanin...

*Jane Wagner* CHAPTER Language ======== - How does the brain derive meaning from language? - Do the processes that enable speech comprehension differ from those that enable reading comprehension? - How does the brain produce spoken, signed, and written output to communicate meaning to others? - What are the brain's structures and networks that support language comprehension? - What are the evolutionary origins of human language? **475** ### The Anatomy of Language and Language Deficits Brain Damage and Language Deficits a. Spontaneously speaking b. Repeating "Chrysanthemum" **a** c. Listening for comprehension "Boy hit girl" Arcuate The Wernicke--Lichtheim Model of Brain and Language \ TAKE-HOME MESSAGES - A left-hemisphere network involving the frontal, parietal, and temporal lobes is especially critical for language pro- duction and comprehension. White matter tracts serve as key structures in the left-hemisphere network. - The right hemisphere does play a role in language, espe- cially in processing the prosody of language. - Language disorders, generally called aphasia, can include deficits in comprehension or production of lan- guage resulting from neurological damage. - People with Broca's aphasia have problems with speech production, syntax, and grammar, but otherwise compre- hend what is said or written fairly well. The lesions that produce Broca's aphasia may not be limited to the classi- cally defined Broca's area in the left inferior frontal cortex. - People with Wernicke's aphasia have severe comprehen- sion deficits but can produce relatively fluid, but often **A** - The arcuate fasciculus is a large neural fiber tract con- necting Broca's and Wernicke's areas. Damage to this tract of nerve fibers results in conduction aphasia. ### The Fundamentals of Language in the Human Brain 1. **Lexical access**, the stage(s) of processing in which the output of perceptual analysis activates word- form representations in the mental lexicon, including their semantic and syntactic attributes. 2. **Lexical selection**, the stage in which the represen- tation that best matches the input is identified 3. **Lexical integration**, the final stage, in which words are integrated into the full sentence, discourse, or larger context to facilitate understanding of the whole message. Organization of the Mental Lexicon 1. The smallest meaningful representational unit in a language is called a **morpheme**; this is also the small- est unit of representation in the mental lexicon. As an example consider the words *frost*, *[de] frost*, and *defrost[er]*. The root of these words, *frost*, forms one morpheme; the prefix "de" in *defrost* changes the meaning of the word *frost* and is a morpheme as 2. More frequently used words are accessed more quickly than less frequently used words; for instance, the word *people* is more readily available than the word *fledgling*. 3. The lexicon is organized in neighborhoods consisting of words that differ from one another by a single let- ter or phoneme (e.g., *bat*, *cat*, *hat*, *sat*). A **phoneme** is the smallest unit of *sound* that makes a difference to meaning. Words with many overlapping phonemes or letters are thought to cluster in the mental lexicon in such a way that when incoming words access 4. Representations in the mental lexicon are orga- nized according to semantic relationships between words. Evidence for this type of organization comes from semantic priming studies that use a lexical decision task. In a semantic priming study, participants are presented with pairs of words. The first member of the word pair is the *prime*, while the second member, the *target*, can be a real word (*truck*), a nonword (like *rtukc*), or a pseudoword Models of the Mental Lexicon Neural Substrates   TAKE-HOME MESSAGES - The mental lexicon is a store of information about words that includes semantic information, syntactic informa- tion, and the details of word forms. - A morpheme is the smallest meaningful unit of lan- guage. A phoneme is the smallest unit of sound that makes a difference to meaning. - Syntax is the way in which words in a particular language are organized into grammatically permitted sentences. - Grammar is the collection of structural rules that govern the composition of words, phrases, and sentences in a particular natural language. - Patients with neurological damage may name an item's category or a semantically related word instead of the item (e.g., "animal" for "horse"), which supports the idea that the mental lexicon contains semantic networks of words having related meanings clustered together. - Categories of semantic information are represented in the left temporal lobe, with a progression from posterior to an- terior for general to more specific information, respectively. 3. ### Language Comprehension: Early Steps -- -- -- -- -- -- Spoken Input: Understanding Speech High Low Speech sensitivity Written Input: Reading Words **a** 0 input is temporarily stored as an iconic memory by the R  TAKE-HOME MESSAGES - Sound comprehension involves the superior temporal cortex. People with damage to this area may develop pure word deafness. - Distinguishing speech from nonspeech sounds occurs in the superior temporal sulcus (STS) surrounding early auditory cortex. Distinguishing words from nonwords involves the middle temporal gyrus, inferior temporal - Written-word processing takes place in a region in the occipitotemporal cortex of the left hemisphere. Damage to this area can cause pure alexia, a condition in which patients cannot read words, even though other aspects of language are normal. - Written information from the left visual field first arrives via visual inputs to the contralateral right occipital cortex and is sent to the left-hemisphere visual word form area via the corpus callosum. - The visual word form area is heavily interconnected with regions of the left perisylvian language system, including in- ferior frontal, temporal, and inferior parietal cortical regions. 4. ### Language Comprehension: Later Steps The Role of Context in Word Recognition 4. *Modular models* (also called autonomous models) claim that normal language comprehension is executed within separate and independent modules. Thus, higher-level representations cannot influence lower-level ones, and therefore the flow is strictly data driven, or bottom-up. 5. *Interactive models* maintain that all types of informa- tion can participate in word recognition. In these models, context can have its influence even before the sensory information is available, by changing the activational status of the word-form representations in the mental lexicon. McClelland and colleagues (1989) proposed this type of interactivity model, as noted earlier. 6. *Hybrid models*, which fall between the modular and interactive extremes, are based on the notion that Integration of Words Into Sentences Semantic Processing and the N400 Wave 1. Normal sentences that ended with a word congruent with the preceding context, such as "It was his first day at work." 2. Sentences that ended with a word anomalous to the preceding context, such as "He spread the warm bread with socks." 3. Sentences that ended with a word semantically congruent with the preceding context but physically deviant, such as "She put on her high-heeled SHOES." N400 P560 \ Syntactic Processing and the P600 Wave Grammatically correct +--------+--------+--------+--------+--------+--------+--------+--------+ | | | | | | | | | +--------+--------+--------+--------+--------+--------+--------+--------+ | | **verw | | | | * | | | | | d | | | | *speel | | | | | | | | | goed** | | | +--------+--------+--------+--------+--------+--------+--------+--------+ a. Semantic N400 b. Left anterior negativity (LAN) 250--300 ms 300--350 ms 350--400 ms 400--450 ms 450--500 ms 500--550 ms 550--600 ms Semantic Syntactic a. Horizontal section b. Coronal section  TAKE-HOME MESSAGES - Lexical selection can be influenced by sentence context. - Lexical access and selection involve a network that includes the middle temporal gyrus (MTG), superior tem- poral gyrus (STG), and ventral inferior and bilateral dorsal inferior frontal gyri (IFG) of the left hemisphere. - The left MTG and STG are important for the translation of speech sounds to word meanings. - Syntactic parsing is the process in which the brain as- signs a syntactic structure to words in sentences. - In the ERP method, the N400 is a negative-polarity brain wave related to semantic processes in language, and the P600/SPS is a large positive component elicited after a syntactic and some semantic violations. - Syntactic processing takes place in a network of left inferior frontal and superior temporal brain regions that are activated during language processing. ### Neural Models of Language Comprehension 7. *Memory* refers to the linguistic knowledge that, fol- lowing acquisition, is encoded and consolidated in neocortical memory structures. In this case, memory is language-specific information. Knowledge about the building blocks of language (e.g., phonologi- 8. *Unification* refers to the integration of lexically retrieved phonological, semantic, and syntactic information into an overall representation of the whole utterance. In language comprehension, the 9. *Control* relates language to social interactions and joint action (e.g., in bilingualism and in taking turns during a conversation). Networks of the Left-Hemisphere \ TAKE-HOME MESSAGES - Models of language comprehension involve the idea of unifying information from linguistic inputs or from re- trieved linguistic representations to create new and more complex linguistic structures and meanings. - White matter tracts in the left hemisphere connect inferior frontal cortex, inferior parietal cortex, and temporal cortex to create specific circuits for linguistic operations. ### Neural Models Motor Control and Language Production Psycholinguistic Models of Speech Production Neural Substrates of Language Production Shared Intentionality and we tend to think communication is intentional. When we are looking for the origins of language, how- TAKE-HOME MESSAGES - Speech production involves the use of orofacial muscles that are controlled by processes using internal forward models and sensory feedback. - Models of language production must account for the processes of selecting the information to be contained in the message; retrieving words from the lexicon; plan- ning sentences and encoding grammar using semantic and syntactic properties of the word; using morphologi- cal and phonological properties for syllabification and prosody; and preparing articulatory gestures for each syllable. - Each stage in Levelt's model for language production occurs serially, and its output representation is used for input to the next stage. The model avoids feedback, loops, parallel processing, and cascades. The early stages of this model fit well with the findings of ERPs recorded intracranially. - Hickok's model of speech production involves parallel processing and two levels of hierarchical control. ### Evolution Gesture and Communication Left-Hemisphere Dominance and Specialization \ TAKE-HOME MESSAGES - Nonhuman primates' vocalizations can carry meaning and show evidence of rudimentary syntax. In general, however, animal calls tend to be inflexible, associated with a specific emotional state, and linked to a specific stimulus. - Some researchers suggest that human speech and language evolved from hand gestures, or a combination of hand gestures and facial movement. - The greatest evolutionary brain changes we know of involve the size and function of the left temporal cortex and, importantly, how this cortex is interconnected with inferior frontal and parietal cortex. #### Summary What has emerged is the left perisylvian language sys- tem, which has elaborate white matter connections between #### Key Terms  #### Think About It 10. How might the mental lexicon be organized in the brain? Would we expect to find it localized in a particu- lar region in cortex? If so, where, and what evidence supports this view? 11. At what stage of input processing are the comprehen- sion of spoken language and the comprehension of written language the same, and where must they be different? Are there any exceptions to this rule? 12. Describe the route that an auditory speech signal might take in the cortex, from perceptual analysis to comprehension. 13. What evidence exists for the role of the right hemi- sphere in language processing? If the right hemisphere has a role in language, what might that role be? 14. Can knowledge of the world around you affect the way you process and understand words? 15. Describe the anatomy and circuitry of the left peri- sylvian language system, and how it has changed over the course of primate evolution. #### Suggested Reading **513**