Reaction papers

• 1 summary paragraph; 3 or more comments (separate paragraphs)

• Format: ok to use single space; 1” margins

• No quotes

• Try to use formal language (e.g. no contractions) (although first person is fine)

• Try to keep comments about article (not about CogLab).

• No final conclusion paragraph needed

• If confusing, look up info or try to resolve. Do not say ‘I didn’t understand it.’

• If ask questions or suggest future studies, provide what you think you would find (hypotheses)?

Our Divided Brain

• Corpus Callosum

– large bundle of

neural fibers

– connects the two

hemispheres

– carries messages

between the

hemispheres

Corpus Callosum

Split-brain patients

• Gazzaniga et al. (1962)

• Documentary • http://www.youtube.com/watch?v=MZnyQewsB_Y

• “Joe” • http://www.youtube.com/watch?v=aCv4K5aStdU&feature=related

• Scientific American Frontiers • http://www.youtube.com/watch?v=W9iNMxjxL7k&feature=related

• Brain Story BBC documentary • http://www.youtube.com/watch?v=fCwIhztgTv4

Our Divided Brain

• Path of

information from

the eyes to the

brain

• Contralateral

control

Brain Asymmetry

• Hemispheric specialization = separate functions for

each hemisphere

• Method: Split-brain patients (Gazzaniga)

– Asked to verbally report words/pics flashed on a screen

– Right side of screen -> left hemisphere -> say word

– Left side of screen -> right hemisphere -> “???”

• Conclusions:

• Left brain: language and analytical thought

• Right brain: spatial relations and creativity

Left Brain, Right Brain?

• Left:

• Verbal

• Sequential

• Logical

• Plans ahead

• Remembers names

• Looks at parts

• Right:

• Visual/spatial

• Random

• Emotional

• Impulsive

• Remembers faces

• Looks at whole

http://www.playcranium.com

Cranium: “The game for your whole brain”

CogLab: Brain Asymmetry

• Question

– Is the brain lateralized in normal participants?

– Is the right hemisphere more responsible for facial judgments about age

• Method

– Decide which of 2 chimeric faces is “youngest”

– IV: youth side, IV: handedness, DV: % left choice

• Hypothesis

– Choose face with younger-half when on left side (b/c info processed by right hemisphere)

– Stronger effect for righties vs lefties

CogLab: Brain Asymmetry

• Results (global; class)

– % chose yng-half of face when on left side

– Righties: N=21,809; 57.3% (sd = 19.8%) (class N=12, 53%)

– Lefties: N=2,273; 56.5% (sd = 19.5%) (class N=1, 42.9%)

• Discussion

– Left side of face (LVF) more influential in age decision

therefore, right hemisphere (RH) bias

– Support for lateralization

– CogLab: Same or less effect in lefties vs. righties?

• Comments? Confounds? Future directions?

Handedness and Lateralization

• Strong but imperfect correlation between handedness and

lateralization

– http://faculty.washington.edu/chudler/split.html

• Strongest lateralization in right-handed males

• 90% of population is right-handed

– 95% of righties use Left hemisphere for language

• 10% of population is left-handed

– 70% of lefties use Left hemisphere for language

– 30% of lefties use both hemispheres for language

• Problem: How do you define and measure handedness?

Heller & Levy (1981)

• Hypothesis

– LVF (left visual field) dominates discrimination of facial

emotion

– Emotion expression greater on left side of face

– Greater lateralization for righties vs. lefties

• Method

– 12 righties & 12 lefties for discrimination task

– Photographs of righties & lefties neutral & smiling

– Chimeric faces presented successively for 150ms

– Judgment: Which looked happier?

Heller & Levy (1981)

• Chimeric faces

Rl Lr

Rr Ll

Heller & Levy (1981)

Heller & Levy (1981)

Heller & Levy (1981)

• LVF preference for discrimination (or perception) of facial emotion

– Moderate effect for righties, no effect for lefties

– Hemispheric specialization is heterogeneous

• Expression of emotion more on left side of face

– For both righties and lefties

– But, large individual differences in facial asymmetry too

• Future directions

– Examine Ss with greater expression asymmetry to see if greater LVF preference for discrimination

– Other suggestions?

Butler & Harvey (2006)

• Question

– Is left perceptual bias due to practiced directional scanning bias (read left to right)?

• Method

– Present faces too quick (100ms) so that eye movements are impossible

– Used realistic male/female face stimuli

– Gender judgment (rather than emotion)

• Results/Discussion

– 55% of responses based on left side of face

– 13 of 15 Ss showed left bias

– Bias stronger when eye movements are possible (longer PT – LVF bias = 63%)

Ashwin, Wheelright & Baron-Cohen (2005)

• Question

– Do people with Asperger syndrome (AS) have same LVF

biases for face identity and emotional expression face tasks?

• Method

– Exp1: Chimeric faces: angry, happy (which one is more?)

– Neutral condition (which has more stars?)

– Exp2: Chimeric faces: (which looks like original?)

• Laterality bias score= # LVF - # RVF/ total

– Positive scores = LVF bias

Ashwin, Wheelright & Baron-Cohen (2005)

Which face

looks more:

angry / happy?

Which display

has more stars?

Ashwin, Wheelright & Baron-Cohen (2005)

Identity perception task: Which face is same as original?

Application of Lateralization research

Heller, Nitschke, & Miller (1998)

• Right hemisphere regulates emotion

• Research suggests:

– Understanding emotion: right lateralized

– Expressing emotion: right lateralized

– Feeling emotion: not lateralized

• Application:

• Individuals had following “symptoms”:

– Poor visuo-spatial information processing

– Difficulty in understanding interpersonal processes

• All right lateralized problems – led to diagnosis of “non-verbal learning disability” (NVLD)

– Research assisted diagnosis

Summary

• Split-brain research provided evidence for

– Hemispheric specialization

– Corpus callosum integrates info from 2 hemispheres

• One hemisphere more efficient in a cognitive process, not

solely responsible

• Difficult to get lateralization effect in normal population

– In part due to handedness? Gender? Other?

• Research helped identify types of emotion and NVLD

• Final question:

– Why do hemispheres specialize?