Chapter 19 Summary & Outline

The Development and Evolution of Speech and Language Are Remarkable

• Languages are made up of speech sounds, called phonemes and morphemes, that are assembled into words and sentences according to syntax.
• Humans are distinct in the animal kingdom for their language and associated cognitive abilities. Possible evolutionary origins of human speech may be seen in aspects of gestures.
• Humans are born with an innate mechanism for acquiring language during an early sensitive period. Aspects of language acquisition appear to be controlled by genes like FOXP2. Other genes appear to be crucial for language articulation. Review Figure 19.1
• Studies of communication among nonhumans provide analogies to human speech. For example, the control of birdsong is lateralized in the brains of some species of songbirds, and early experience is essential for proper song development. Review Figures 19.2 and 19.3, Web Activity 19.1
• Nonhumans lack the peripheral apparatus to produce speech, but nonhuman primates like the chimpanzee can learn to use the signs of American Sign Language. However, controversy surrounds claims that these animals can arrange signs in novel orders to create new sentences.

Study questions: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13

Language Disorders Result from Region-Specific Brain Injuries

• Language impairment due to brain damage (aphasia) is much more likely after injury of the left cerebral hemisphere than the right hemisphere. Left inferior frontal lesions produce an impairment in speech production called nonfluent (or Broca’s) aphasia. More-posterior lesions, involving the temporoparietal cortex, cause fluent (or Wernicke’s) aphasia. Extensive destruction of the left hemisphere causes a more complete loss of language called global aphasia. Review Figures 19.6 and 19.7 and Table 19.1, Web Activity 19.2
• The Wernicke-Geschwind model of aphasia emphasizes a loop from a posterior speech reception zone to an anterior expressive zone. In contrast, the motor theory of language suggests that the entire circuit serves motor control and is used for both production and perception. Nonhuman primates lack this specialization. Review Figure 19.8, Web Activity 19.3
• Left-hemisphere lesions in users of sign language produce impairments in the use of sign language that are similar to impairments in spoken language shown by nondeaf individuals suffering from aphasia.

Study questions: 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21

Reading Skills Are Difficult to Acquire and Frequently Impaired

• Acquired dyslexia is a difficulty with reading resulting from brain damage, usually in the left hemisphere. In deep dyslexia there is a disturbance in reading whole words; surface dyslexia involves a difficulty with the sounds of words.
• Developmental dyslexia is a congenital difficulty with reading that is associated with brain abnormalities. Several brain systems have been identified in developmental dyslexia. Abnormalities in any of several different genes may predispose an individual to dyslexia. Review Figure 19.10

Study questions: 22 | 23 | 24 | 25 | 26

Brain Stimulation Procedures Provide Information about the Organization of Language in the Brain

• Electrical stimulation during brain surgery has confirmed the left-hemisphere organization for language functions. Stimulation within anterior regions causes speech arrest, while stimulation in other locations causes misnaming and other speech errors. Review Figure 19.11
• Mapping with transcranial magnetic stimulation provides a way to create temporary “virtual lesions” in speech zones. TMS studies are revealing fine divisions within traditional speech zones in the brain. Review Figure 19.12

Study questions: 27 | 28

Functional Neuroimaging Portrays the Organization of the Brain for Speech and Language

• Studies using PET and fMRI reveal that distinct regions of the left hemisphere are active during viewing, hearing, repeating, or assembling verbal material. Review Figure 19.13
• ERP recordings reveal that the left hemisphere of the brain processes semantic content and grammar.

Study questions: 29 | 30 | 31 | 32

Williams Syndrome Offers Clues about Language

• In Williams syndrome, deletion of a relatively small number of genes from chromosome 7 produces a set of symptoms including excellent verbal function and sociability against a background of impaired general reasoning.

Study questions: 33

The Left Brain Is Different from the Right Brain

• Split-brain individuals show striking examples of hemispheric specialization (lateralization). Most words projected only to the right hemisphere, for example, cannot be read, but the same stimuli directed to the left hemisphere can be read. Spatial tasks, however, are performed better by the right hemisphere than by the left. Review Figure 19.15
• Normal humans show many forms of cognitive specialization of the cerebral hemispheres, although these specializations are not as striking as those shown by split-brain individuals. For example, most normal humans show an advantage for verbal stimuli presented to the right ear or right visual field. Review Figure 19.16
• Anatomical asymmetry of the hemispheres is seen in some structures in the human brain. Especially striking is the large size difference in the planum temporale (which is larger in the left hemisphere than in the right hemisphere of most right-handed individuals). Nevertheless, in most cases mental activity depends on interactions between the cerebral hemispheres. Review Figure 19.17
• About 10% of people are left-handed, but most of these nonetheless show left-hemisphere lateralization for language.

Study questions: 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44

Deficits in Spatial Perception Follow Right-Hemisphere Damage

• In most patients, parietal cortical injuries produce perceptual changes, including alterations in sensory and spatial processing.
• Damage including the fusiform gyrus can produce acquired prosopagnosia, a dramatic inability to recognize the faces of familiar people. A congenital form of prosopagnosia affects about 2.5% of the population. Review Figures 19.18 and 19.19

Study questions: 45 | 46 | 47

Following Some Injuries, the Brain Can Recover Function

• Much of the damage following brain injury can show at least partial recovery of function, especially during the first year or so, as the damaged brain stabilizes.
• Retraining is a significant part of functional recovery and may involve both compensation, by establishing new solutions to adaptive demands, and reorganization of surviving networks. Review Figure 19.20

Study questions: 48 | 49 | 50 | 51 | 52 | 53