Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.1 Hemispheric Asymmetry Anatomy and pathways –animal comparisons Tests of hemispheric specialization Variations in organization Theories of hemispheric specialization Development

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.2 Hemispheric Asymmetry Pathology –unusual patterns of asymmetry –dysfunction of one hemisphere Cognitive Style –education –occupation

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.3 Anatomy and Pathways The brain appears symmetric although divided down the center from front to back There are four main lobes on each side –frontal - thought and planning –parietal - motor and touch –temporal - hearing –occipital - vision

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.4 Anatomy and Pathways

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.5 Anatomy and Pathways In general the brain receives from and sends information to the opposite side of the body –contralateral The organization in vision is more complex –optic chiasm –right visual field is projected to left hemisphere and left visual field to right hemisphere

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.6 Anatomy and Pathways Nasal hemiretina

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.7 Anatomy and Pathways Not completely symmetric –temporal lobe is slightly larger in LH –men often have slightly larger RHs First notice functional difference in aphasia –more likely with LH damage –women more likely to suffer less and recover more than men Animal comparisons –some “handedness” evidence (paws and tail curling) –song bird that loses and re-grows left hemisphere temporal lobe each mating season

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.8 Tests of Hemispheric Specialization Brain damage –look at location of loss and cognitive ability lost –aphasias –problem - not controlled, patients often recover functions Split-brain patients –cut corpus callosum (band of fibers connecting the two hemispheres of the cortex) –present stimuli to each hemisphere –initially large differences –over time only subtle differences

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.9 Tests of Hemispheric Specialization Brain activity assessment –EEG - correlate electrically activity with cognitiive activity –PET scan - (CAT scan) usually look for damage –Evoked potentials - neuro-electrical response to stimuli –fMRI - watch ongoing change in activity with cognitive task The Wada test –sodium amytal injection - put one hemisphere to “sleep” Dichotic listening –Kimura Effect - right ear dominance for speech

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.10 Tests of Hemispheric Specialization Tachistoscopic presentation –different information to each visual field –presented too fast for an eye-movement Kinsbourne tests –lateral eye movements triggering activation in one hemisphere causes eye movements in the opposite direction –multiple tasks vocalize and use limbs at the same time hard to do right handed balancing or tapping when speaking

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.11 Variations in Organization Left-handedness –inverted left-hand writers often have language in right hemisphere –left-handers who do not do inverted writing may be less lateralized Gender –men are more lateralized, women are less lateralized –women suffer less language loss from left hemisphere damage because language is more evenly distributed –it has been argued that men’s superior spatial skills are due to their right hemisphere being totally dedicated to spatial tasks –the basis for the gender difference is unclear genetic hormonal environment (social)

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.12 Variations in Organization Maturation rate –people who reach puberty earlier are less lateralized –interaction with gender difference since women tend to mature faster

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.13 Theories of Hemispheric Specialization Language theory –LH specialized for language –RH specialized for spatial tasks Coding theory –LH uses analytic code –RH uses analog code Processing theory –LH - analytic, parts, logic –RH - gestalt (wholistic), global, emotional Processing theory 2 –LH - high resolution, later analysis (details) –RH - low resolution, early analysis (gist)

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.14 Development Some differences at birth –anatomy –evoked potentials Plasticity –children recover from very early brain damage –mono-hemispheric children –brain anomolies show early rewiring Critical Periods –early exposure to stimuli critical for normal development

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.15 Pathology Unusual patterns of asymmetry (controversial) –stuttering competition between the hemispheres for the control of speech left hand inverted writers are more likely to stutter left handers forced to use their non-preferred hand –dyslexia left-ear advantage in dichotic listening language in right hemisphere some have argued that a lack of lateralization may influence dyslexia, but men are more likely to be dyslexic than women (and women are generally less lateralized)

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.16 Pathology Dysfunction of one hemisphere –schitzophrenia more likely after damage to LH EEGs show more abnormal activity in LH may be lack of normal communication between hemipsheres –depression more likely after damage to RH EEGs show more abnormal activity in RH shock treatment need only be done in RH –LH damage usually lose language –RH damage emotional disruption unilateral neglect syndrome

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.17 Cognitive Style Left Hemisphere –verbal –sequential –time oriented –digital –logical –analytical –rational – western Right Hemisphere –non-verbal –simultaneous –spatial –analog –Gestalt –synthetic –intuitive –emotional –eastern

Cognitive - hemispheric_asymmetry.ppt © 2001 Laura Snodgrass, Ph.D.18 Cognitive Style Cultural Differences –what style of thinking is valued Education –college majors –teaching and learning styles –gender differences –types of creativity –does American education short change the RH –RH as pattern finder and LH for critical analysis Occupations –artists, architects, counselors –lawyers, scientists