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Ted Petit

TYPE THE DOCUMENT TITLE Pick the dateModule 41 Methods Laterality the functional specialization of the right and left hemispheresBroca was first to popularize the functional specialization of each hemisphere Left HemisphereSpecialized for language and control of the right hand and fingers Right HemisphereHughlingsJackson played a role in visual information of objectsSpecialized for music emotion and spatial abilities and control of the left hand and fingers Understanding of functions of right hemisphere took longerpoor linguistic ability Cognitive deficits resulting from RH damage tend to be subtle in comparison to the significant linguistic impairments that follow LH damage Tends to make it difficult to obtain information regarding its function Neurologically normal brain function relies on constant communication between RH and LH Both hemispheres have some degree of competency for most functions Eg When someone say the words nice shoes o Left Braininterprets sound waves that make up the speech and interpret it as the words nice shoes o Right braininterpret sound waves that compose the emotional tone of the speech and allows interpretation the comment as either a compliment or an insultFailure to communicate between RH and LF becomes especially essential in ambiguous situations when interpretation of stimuli is important to come to a correct conclusion Split BrainWhen the corpus callosum is severed the information that is received from the right visual cortex can no longer be integrated with that of the right visual cortex Results in a brain that is split into two separate halves that can no longer communicate with each other Information can no longer influence the other hemisphere Hemisphere can transmit pathology One form of epilepsy uses the commissural systems to involve both hemispheres in the production of severe seizure activityo Complete commissurotomies is successful treatment for epilepsyfrequency and severity of seizures were reduced Complete commissurotomies results in two hemispheres that are intact but separate Motor visual auditory and somatosensory abilities of each hemisphere are intact Allowed learning that RH is capable of language although also specialized for other functionso Although RH is largely unable to either speak or write it is capable of arranging letters to spell 3 or 4 letter words capable of comprehending spoken and written wordso Special role in recognition of facesLevy used 2 differenthalves of faces that were combined to make one face and participant had to pick out which whole face they had observedTYPE THE DOCUMENT TITLE Pick the date Two hemispheres saw different faces Most of the time the participants picked the face that had appeared in the left visual field which sends information to the RH Intracarotid Amobarbital Testing IATAka Wada testreflects role of Juhn Wada who used pioneered its use in the late 1940s Commonly used to assess the laterality of language in individuals who will be undergoing brain surgery Sodium amobarbital shortterm anesthetic is injected into the either right or left internal carotid artery which anaesthetizes the hemisphere ipsilateral to the injection Typically the individual has his or her contralateral arm in the aironce the hemisphere is anaesthetized it no longer maintains motor control over the contralateral limb and the arm drops Tends to last for a period of minutes during which cognitive functions of the unanaesthetized hemisphere can be examined Goal to assess the language and memory capabilities of the two hemispheres independently of each other Many variations of IATMost attempt to measure expressive and receptive language ability and shortterm and longterm memory Revealed that most individuals exhibit LH dominance for speech although some individuals exhibit either bilateral or RH dominance for languageLanguage functions of brain may vary with hand dominance RH language occurs more frequently in lefthanders Bilateral representation of speech does not mean that language function is dispersed equally across the two hemispheresexhibits some type of interference with different language functions Very invasive procedureVisual SystemThe visual system sends information from receptors located in the retina of both eyes to both hemispheresbut information is segregated with respect to where the item was viewed in space Visual information presented in the left visual field is transmitted to the primary visual cortex of the RH from the nasal hemiretina of the left eye and the temporal hemiretina of the right eye Visual information presented in the right visual field is transmitted to the primary visual cortex of the LH from the temporal hemiretina of the left eye and the nasal hemiretine of the right eye Information is perceived in the visual cortex of one hemisphere is communicated to the other hemisphere via the corpus callosumDivisions of information between the hemiretinas occurs only in the periphery of the retinafovea center of the retina that is used for fine detail and color vision automatically transmits information to both the right and left visual cortex Techniques that investigate laterality of visual functions must take care to present stimuli peripherally and not to allow the fovea to observe the stimulus TYPE THE DOCUMENT TITLE Pick the dateo Achieved by having the participant stare at a point at the center of the screen while keeping the stimulus away from the center of the visual field 1 degree from the centero Stimuli is presented very briefly 150ms o Allows eyes to have no chance to make movements from center of the screen preventing the fovea from viewing the stimulus and sending the information to both hemisphere Auditory SystemIs not as segregated as the visual systemall receptors in the cochlea send projections bilaterally auditory information received in one ear is sent to both hemispheres Projections to the ipsilateral hemisphere are weaker andless numerous and send information more slowly than projections to the contralateral hemisphere do Although both hemisphere can attend to stimuli presented to either ear situations in which information must compete result in the domination of contralateral projections o When competing stimuli are presented to the two ears simultaneously the RH will preferentially attend to the input from the left ear and vice versa Information is sent to the other via the commissural systems Dichotic ListeningTakes advantage of the suppression of ipsilateral projections that takes place when stimuli compete with each other Dichotic listening tasks present different stimuli to each ear Stimuli words music emotional tones phonemes Participant are asked to either report what they heard or to listen for a target and to indicate whether the target was present or not o Number of correct responses is tallied for each ear and an asymmetry score is computed Dichotic listening tasks that use words or phonemes as stimuli tend to result in an asymmetry score that favours the right ear Reflects the transmission of the stimulus from the right ear over the stronger larger and faster contralateral pathway to the LHMost people exhibit LH language functionsLH is better able to comprehend and report word or phoneme stimuli Some people with RH language functions exhibit asymmetries that favour the left ear Dichotic listening studies tend to report that there are more people who have RH language functions than either IAT or splitbrain studies do Overrepresentation of RH language is an artifact of the testing conditionDichotic tasks are not pure measures of laterality and that overrepresentation of RH language reflects the impurities in the taskwhen individuals are directed to attend to a specific ear they can modify their asymmetry scores Dichotic listening tasks that use music environmental sounds or emotional tones as stimuli tend to result in an asymmetry score that favours the left ear Suggests that the RH is specialized for the processing of nonlinguistic sounds such as music and prosody
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