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Chapter 2

Chapter 2 – Biological Foundations of Sensory Perception.doc

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McGill University
PSYC 212
Remy Allard

Chapter 2Biological Foundations of Sensory PerceptionOrganization of the Nervous SystemBrain is a heterogenous collection of functionally specialized structures or areas and the opposing view of the brain as a homogeneous organ in whciht he various functions of the mind are diffuse and synergisticFunctional specializationhistoryFranz Joseph Gall Austrian physician proposed human brain divided into precise anatomical modulesresponsible for different mental functionsoFunctions vary from most basic perceptions to highest levels of human behaviour ie generosity spirituality self esteemoGall postulated three dozen faculties postulated by Gall to occupy defined locations on the surface of the brainoActual locations were identified through inference after studying fieldsassociatescorrelating their behavioural characteristics to external feature of the skulloBelieved bumps and depressions on the skull related to underlying brain matterIf one part of the brain is large they were blessed and well developedPhrenologyfirst complete theory of cerebral localizationoBehavioural characteristics could be assessed by external landmarks on the skulloNot a good science but stimulated thinking and experimentation on question of functional specialization in the brainoTwo formsLesion studiesanimals for behavioural analysisStudy of clinical cases in humans who suffered some form of brain damageoFlourens able to disrupt certain motor functions but unable to find deficits in more elaborate forms of behaviourNo localization of functioninjury to any part of the brain affects all higher functions equallythClinical and experimental studies in the 19 centurythoFunctional specialization really took place in middle of 19 century with clinical studies on humansoPierre Paul Broca studied a patient who lost ability to speak aphasia oCould understand language and had motor functions in mouth and tongue but couldnt speak grammatically or express ideas in writingoAfter death Broca discovered lesion in frontal part of brain only present in left cerebral hemisphereoOther patients with aphasia had the same thingBroca proclaimed discrete part of the brain Brocas area to be responsible for production of speechoLocalization of speech production did not convince everyone until more studies about functional specializationoie electrical stimulation in one cerebral hemisphere of dogs produced limb movements on the opposite sideoie Carl Wernicke discovering different side of the brain where aphasia affected ability to understand speech to be impaired but speaking okaycame up with theory that compromised two opposing views by taking into account accumulated evidence on functional specializationblending it with idea that mental functions are homogeneously distributed across the brainproposed simple sensory and motor functions localized to discrete brain areas but interaction of modules is responsible for producing more complex aspects of perception action and behaviourlanguageexample ie Brocas area and Wernickes areaPhineas Gage o1848 railway dynamite accident causing iron rod to fly out of his hand into his left cheekbone out through the brain and his skullonot killed briefly lost consciousness then got up and spokeophysical recovery complete after few monthsopersonality changed a lotfrom goodhumoured diligent wellliked to lazy profane illmannered liarolost family and friendsodied of epileptic fit 12 years lateroused to be argument against functional localization and connection of Brocas area to aphasia much damage to frontal lobepersonality changes not widely knownphysicians attempts to argue case for localization rejectedorecent application of modern scientific tools in autopsy of preserved skull showed that injury affected his bodyFunctional specializationmodern viewsadvances in histology produced a better understanding of brain structurehistologythe study of fine structure and organization of a tissue or organ at the microscopic levelneuroanatomists looked at human brain like anatomical divisions defined by basis of differences in fine structure and organization at cellular levellocalization of functions in the human brainoWilder Penfield used electrodes to stimulate brains of patients undergoing surgery for relief of epileptic seizuresoPatients under local anesthesia only therefore remained awake throughout surgeryoBrain tissue itself does not generate any feelings of sensation or pain when it is physically manipulated or damagedoStimulated the brain directly by passing small amounts of electrical current through electrodes to observe the effects through verbal responses from patientsoConfirmed localization of human brain
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