Psych 307 - Hemispheric Specialization

features in the left hemisphere

• searches for causal explanations of phenomenon in the world

• important for routine

features in the right hemisphere

• important for seeking and processing novelty

• works without conscious interpretation (autopilot)

Gazzaniga’s model: example

• chess experts and novices see random chess board configurations for a short period of time

• experts were no better than novices

• if you show one that would occur in a chess game, the experts were better

experts can’t describe their methods because the task was performed by the right hemi (automatic)

Gazzaniga’s model

• talks about automatic brains and interpretive minds

frontal pole

• extends more anteriorly in the right hemisphere

• enlarged posterior regions in the left hemi push the right hemi more anterior

occipital pole

• extends further posterior in the left hemisphere

• common in right handed individuals

planum temporale

• larger in the left hemisphere (10x)

• involved in language and music perception

• asymmetry larger in right handed individuals

angular gyrus

• in the inferior parietal lobe

• integrates multiple sensory systems

• important for complex cognitive functions (i.e. reading, writing)

angular gyrus is larger in…

the left hemisphere

dorsal parietal regions are…

• larger in the right hemi

• important for spatial recognition and spatially guided behaiours

corpus collosum

has more fibres in females

longitudinal fibre pathways in males

• more myelinated

suggestive of better interhemispheric communication

left-handed characteristics

• more likely to have had gestational trauma

• more likely to be dyslexic

• shorter life expectancy

unilateral temporal lobectomies

right temporal lobectomies led to…

• problems with visuospatial memories

left temporal lobectomies led to…

verbal memory deficits

left =

language

right = 

spatial cognition

split brain patients

surgically severed the corpus collosum to reduce severe epilepsy

stops communication between the two hemispheres

wechsler adult intelligence scales

• arrange a picture with cubes that have a red side, white side, and split

• try to arrange the picture 

easier for split brain patients if they do it with their left hand (engages the right hemi - spatial processing)

harder for patients with their right hand (engages the left hemi - language processing)

WADA test 

• patient performs verbal and spatial tasks while one hemi is under anesthesia

• an object is presented beforehand and ask to identify afterward

• accurate responses show the non-anesthetized hemisphere processes language

alien hand syndrome (anarchic hand)

• arises from medial frontal damage

• one hand behaves at odds to their intentions

• interhemispheric co-operation is disrupted and each hand is operating independently

typically occurs in the left hand

right hemisphere - spatial processing

• line orientation

• face discrimination

• pitch/tone discrimination

• emotional regulation/perception

• spatial neglect

these things become problematic when there is damage to this hemi

divided visual field studies 

• done in neurotypical individuals to gauge reaction time and accuracy 

• present stimuli to one hemi or the other

• see a left visual field (or right hemisphere) advantage for spatial material

• see a right visual field (or left hemisphere) advantage for verbal material 

dichotic listening paradigm

• presented a stimuli in the ears

• any bias in reporting what you hear for one ear vs the other suggests a preference in processing in that hemi

• LH recalls let

familiar =

left hemispheric activation

unfamiliar =

right hemispheric activation

material specific account theory

• each hemisphere is specialized for processing a particular kind of stimulus

• fails to take into account that same materials (i.e. written words) can be processed in different ways

(reading silently vs reading aloud)

modes of processing

distinction made between global and local processing

• RH preference for global processing

• LH preference for local processing

global processing

• big picture stimulus

• understanding overall form or context

• tend to see/process quickly

• RH preference

local processing

• smaller, specific details of a stimulus 

• takes some time to process

• LH preference

differential sensitivity account

• each hemi specializes in different frequency ranges, not absolute differences

process is cross-modal

RH frequency

• low

  • coarse coding

  • global object analysis

  • prosody

LH frequency

• high

  • fine-grained coding

  • local object features

  • speech comprehension

direct access theory

the hemisphere that receives information processes it first

collosal relay theory

information not suited to a hemisphere will be transferred to the other preferred hemisphere

• takes time

• may lead to degradation of the information and poorer performance

activating-orienting model

attention to a task increases activation within the hemisphere dominant for that task

anosognosia

inability to recognize own deficits 

• ex. denial of ownership, alzhimers’s 

typical with RH damage