11: Language and Lateralization Cognitive Neuroscience David Eagleman
11: Language and Lateralization Cognitive Neuroscience David Eagleman Jonathan Downar Chapter Outline Speech, Language, and Communcation
Aphasia: The Loss of Language A Language Network Lateralization: The Two Hemispheres Are Not Identical Development and Language 2
Speech, Language, and Communication Speech is the sound output meant to convey meaning. Language is the ability to translate our ideas into signals for another person. Communication is the ability to convey meaning to another person, regardless of the media.
3 Speech, Language, and Communication 4
Aphasia: The Loss of Language Brocas Aphasia Wernickes Aphasia 5 Brocas Aphasia Dysphonia and dysarthria are injuries to
the vocal muscles. Aphasias result from damage to particular areas of the brain. There are more than 10 different named aphasias. 6
Brocas Aphasia This is caused by lesions to the left lateral frontal lobe. This is known as an expressive aphasia, because patients have difficulty expressing language. Writing is equally impaired.
7 Brocas Aphasia 8 Wernickes Aphasia This involves damage to the left superior temporal gyrus.
This is known as a receptive aphasia, because patients have difficulty comprehending language. The speech sounds fluent, but is nonsensical and contains many filler words. 9
Wernickes Aphasia 10 A Language Network The Larger Picture of Language-Specific Regions Dyslexia
Stuttering 11 The Larger Picture of LanguageSpecific Regions The Wernicke-Geschwind model describes the language network Major components include Brocas area,
Wernickes area, and the arcuate fasciculus, which connects them. This model is an over-simplification of the language network. 12 The Larger Picture of LanguageSpecific Regions
13 The Larger Picture of LanguageSpecific Regions There is an elaborate and extensive network of language areas outside the Wernicke-Geschwind model. Nouns and verbs are located in different parts of the brain.
Areas in the left frontal lobe and the left temporal-parietal area are activated only during language tasks. 14 The Larger Picture of LanguageSpecific Regions
15 The Larger Picture of LanguageSpecific Regions 16 The Larger Picture of LanguageSpecific Regions 17
Dyslexia Dyslexia is a developmental disorder in which subjects have difficulty reading. Dyslexia is not due to a sensory problem or intellectual impairment. In surface dyslexia, individuals have difficulty with the appearance of language. In deep dyslexia, individuals have difficulty
with the sound structure of language. 18 Dyslexia Individuals with dyslexia have problems with the left hemisphere language areas. There is less activity in the Wernickes
area, compared with fluent readers. There is compensatory activity in the left anterior language areas and the right hemisphere. 19 Dyslexia
20 Stuttering Individuals who stutter have increased activity in Brocas area, the supplementary motor area, the insula and the cerebellum. They show decreased activity in the auditory regions of the temporal lobe.
21 Lateralization: The Two Hemispheres Are Not Identical Tests for Dominance Apraxia Hemispheric Differences
Two Brains in One? The Case of the SplitBrain Patients Thinking about Cerebral Asymmetry 22 Tests for Dominance The Wada test is used to establish hemispheric dominance for language
before surgery. A barbiturate is injected into one hemisphere to interrupt speech. fMRI-based tests are more precise and less invasive. 23
Tests for Dominance 24 Apraxia The left hemisphere is dominant for language in 92% of right handed individuals and 69% of left handed individuals.
The left hemisphere is also dominant for fine motor control. Apraxia is difficulty performing fine movements out of context. 25 Apraxia
26 Hemispheric Differences The right hemisphere has greater spatial abilities than the left hemisphere. It is also better at perceiving and understanding emotion. Language is already lateralized for babies
at two months of age. The planum temporale is larger in the left hemisphere and may be associated with language fluency. 27 Hemispheric Differences
28 Two Brains in One? The Case of the Split-Brain Patients The two hemispheres are separate but interconnected. The corpus callosum is the major connection between the hemispheres.
Sometimes, this connection is cut to prevent the spread of seizures. Split-brain patients essentially have two independent hemispheres. 29 Two Brains in One? The Case of
the Split-Brain Patients 30 Two Brains in One? The Case of the Split-Brain Patients Split-brain patients can perform two different tasks simultaneously. They can verbally describe a stimulus
presented to the right visual field (which projects to the left hemisphere). They cannot describe a stimulus presented to the left visual field. 31 Two Brains in One? The Case of
the Split-Brain Patients 32 Thinking about Cerebral Asymmetry It may be more efficient to localize linguistic functions in one hemisphere. According to the analytic-synthetic theory,
the left hemisphere is better at analysis and the right is better at synthesis. According to the motor theory, the left hemisphere is better at fine motor control, of which speech is one example. 33
Development of Language Learning Language from Experience Innate Language Tendencies Socially and Emotionally Directed Learning 34
Learning Language from Experience Language is instinctively learned by babies. Children learn language by statistical learning, or observing the patterns in what they hear. The slower articulation of parentese makes it easier for a baby to analyze
language. 35 Learning Language from Experience 36
Learning Language from Experience 37 Learning Language from Experience By nine months of age, babies prefer the
sounds of their own language. Babies lose the ability to hear sounds that are not part of their native language by about one year. 38 Learning Language from
Experience 39 Innate Language Tendencies One theory, universal grammar, is that we are born with the predisposition to learn the grammar of a language. Patterns of language development are
similar across all languages. Children do not hear enough examples of language to explain this innate learning, supporting a universal grammar. 40 Socially and Emotionally
Directed Learning Social interaction is important for learning language. In a study of Mandarin language learners, infants who interacted with the teacher learned more than infants that listened to recordings of the lessons. There may be some language abilities in other species, but that is not agreed upon.
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