Discovery of the Specific Contributions of Left Hemisphere Damage to Aphasia and Apraxia ----APHASIA
-deficit in language comprehension or production due to brain damage, usually on the left.
Apraxia
-difficulty performing movements when asked to do so out of context, also a consequence of damage on the left.
Therefore, damage to left hemisphere affects language and voluntary movement.
Led to concept of cerebral dominance.
Broca's area
-left inferior prefrontal cortex, damage leads to expressive aphasia.
Discovery of the Relation between Speech Laterality and Handedness
-Left hemisphere is speech dominant in almost all dextrals (right-handers) and most sinestrals (left-handers).
Dextral: 92%
Sinestral/ambidextrous: 70%
Sex Differences in Brain Lateralization
-Females may use both hemispheres more often for language tasks than me do (females may be less lateralized).
Other research: hormones and puberty.
Cerebral Lateralization of Function
-Differences between the function of the left and right cerebral hemispheres
Demonstrated by groudbreaking research of Myers and Sperry with cats.
Cerebral commissures connect the two halves of the brain
Split-brain patients have been studied to understan
Split-Brain - Corpus Collosum
-- largest cerebral commissure
Transfers learned information from one hemisphere to the other
When cut, each hemisphere functions independently
Commissurotomy in Human Epileptics
-Commissurotomy limits convulsive activity
Many never have another major convulsion
Developed procedures to test split-brain patients
Differ from split-brain animals in that the two hemispheres have very different abilities - most left hemispheres are cap
Evidence that the Hemispheres of Split-Brain Patients Can Function Independently
-Present a picture of an apple to the right visual field (left brain)
Left hemisphere can tell you what it was
Right hand can reach under ledge and pick out apple.
If the nonspeaking right hemisphere were asked to indicate the identity of an object that h
cross-cueing
facial feedback from the other hemisphere
For example: the right hemisphere might make the face frown when the left hemisphere gives an incorrect spoken answer
Doing Two Things at Once
Each hemisphere of a split-brain patient can learn independently and simultaneously
Helping-hand phenomenon
presented with two different visual stimuli, the hand that "knows" may correct the other
Chimeric figures task
only symmetrical version of right half of faces recognized (indicates competition between hemispheres)
-The left hemisphere of a split-brain patient sees a single normal face that is a completed version of the half face on the right. At the same time, the
visual completion
-individuals with scotomas(an area of depressed vision in the visual field, surrounded by an area of less depressed or of normal vision) are often unaware of them because their brains can fill them in or complete them by using info form the surrounding.
-
Examples of cerebral laterization: superiority of the left hemisphere in controlling ipsilateral movement!
-when complex, driven moments are made by one hand, most of the activiation is observed in the contrlateral hemisphere. However, some activation is also observed in the ipsilateral hempisphere.
-these ipsilateral effects are greater in the left than the r
superiority of the right hemisphere in spatial ability
-the right hemisphere is superior to the left at spatial tasks
-disorders of spatial perception tend to be associated with right hem. damage
specialization of the right hemisphere for emotion.
-right hem. is superior to the left at performing on some tests of emotion like identifying facial expressions of emotions
superior musical ability of the right hemisphere.
-the right ear (left hem) was superior in the perception of digits, whereas the left ear (right hem) was superior in the perception of melodies.
-right temporal lobe lesions are more likely to disrupt music discriminations that are the left temporal lobe
hemispheric differences in memory
-The two hemispheres have similar abilites that tend to be expressed in different ways. they both have the ability to perform on tests of memory, but the left hem. is better on some tests, whereas the right is better on others.
-the left hem is found to p
the left hemisphere interpreter
-the cognitive approach that is typical of the left hem. is attributed to a mechanism that is metaphorically referred to as the interpreter: a nuronal mechanism that continuously assesses the patterns of events and tries to makes sense of them.
Historical Antecedents of the Wernicke-Geschwind Model
-Broca's area - speech production
Damage leads to expressive aphasia
Normal comprehension; speech is meaningful, but awkward
-Wernicke's area - speech comprehension
Damage causes receptive aphasia
Poor comprehension; speech sounds normal, but has no meani
Wernicke-Geshwind Model
-Involves seven components, all of which are in the left hemisphere
Seven components of the Wernicke-Geshwind Model
-primary visual cortex, angular gyrus, primary auditory cortex, Wernicke's area, arcuate fascicilus, Broca's area, and primary motor cortex
How the Wernicke-Geshwind Model works?
-when you are having a convo, the auditory signals triggered by the speech of the other person are received by ur primary auditory cortex and conducted to Wernicke's area, where they are comprehended. If a response is in order, Wernicke's area generates t
Wernicke-Geschwind Model: The Evidence
-Lack of evidence that damage to various parts of the cortex has expected effects
Surgery that destroys only Broca's area has no lasting effects on speech
Removal of much of Wernicke's area has no lasting effects on speech
Using CT and MRI techniques, hav
Current Status of the Wernicke-Geschwind Model
Empirical evidence supports two elements
Important roles played by Broca's and Wernicke's - many aphasics have damage in these areas
Anterior damage associated with expressive deficits and posterior with receptive
No support for more specific predictions
cognitive Neuroscience Approach: Premise 1, Language
-the use of language is mediated by activity in all areas of the brain that participate in the cognitive processes involved in the particular language related behavior
-BUT each of these processes in the combo of several cognitive processes, which may be
cognitive Neuroscience Approach: Premise 2
- area of the brain involved in language are not dedicatede solely to that purpose
-large areas of the left cerebral cortex were thought to be dedicated to solely laguage, whereas the cognitive neuroscience approach assumes that many of the cognitive proc
cognitive Neuroscience Approach: Premise 3
-Because many areas of the brain that perform specific language functions are also parts of other functional systems, these areas are likely to be small, widely distributed, and specialized.
-the language areas of the model are assumed to be large, circum
dyslexia
reading difficulties not due to some other deficit (e.g., vision, intelligence)
developmental dyslexia
-type of dyslexia
-apparent when learning to read
Heritability estimate = 50%
More common in boys than girls
Developmental Dyslexia: Developmental Dyslexia: Causes and Neural Mechanisms
Brain differences identified, but none seems to play a role in the disorder. Many pathological changes identified, difficult to sort out because no one pathology in all cases.
Multiple types of developmental dyslexia - possibly multiple causes. Also, the
aquired dyslexia
Due to brain damage
Relatively rare