Transcript Research Methods - Victoria University of Wellington

Hemispheric Specialisation
ref. Banich, Ch 4, pp. 113-130
Examples of "popular" view
•“Right-brained people This means that the right side of your
brain is your dominant side. Usually this is the case with
most left-handed people... Right-brained people are usually
very good problem solvers and much more creative… Often
they are also very visual, learning better by visual images
rather than auditory instruction…”
•“Left-brained people This means that the left side of your
brain is dominant. Many times a left-brained person is righthanded... Although left-brained people are not quite as
creative, but are much more logical or analytical than their
right-brained counterparts. Many times, these individuals are
better at science and math…”
•“...as high as 65% of students are now right-brained, as
opposed to back in the 40’s and 50’s when that percentage
Examples of "popular" view
• “Biologists figured out years ago, that the left hemisphere of the brain
is the seat of most logical thought, and the right half of the brain is
where most creativity occurs...”
• “…In most people, the two halves of the brain have difficulty passing
information back and forth. Scientists discovered this by studying
head-trauma patients. In most people, the left half of the brain is
jealously dominant. This, also, has been shown by studying headtrauma patients. These two principles coordinate to insure most
people in our society are quite logical, and not very creative.”
• from http://www.mitra.net.id/business/course/171098.htm
Examples of "popular" view
• “… Betty Edwards, director of the center and author of the best selling
book "Drawing on the Right Side of the Brain," insists anyone can
learn to draw provided they use their right brain functions, as opposed
to the left.... Edwards realized that those who could draw were using
images formed in the right side of the brain and those who could not
were attempting to draw from the logical left side.”
• “… Edwards’ first step in teaching students to draw from the right side
of the brain begins by having students recreate a picture while the
picture is upside down..”
• from http://www.acs.csulb.edu/~d49er/Issue28/28nbrain.html
Hemispheric Specialisation:
Methods of Studying
1. Individuals with unilateral lesions
2. WADA Technique
3. "Split Brain" patients
4. Lateralised presentation
(e.g. visual half-field technique)
1. Individuals with Unilateral
Lesions
• Compare effects of damage to RH and
LH
Does damage result in different types of
impairments in each case?
Left hemisphere damage
•Bill Reiger had been a rising star in high school academically talented and a top athlete. But then
his mother died unexpectedly. Confused by her
death, he turned down a scholarship to college and
joined the army. During a combat mission in
Vietnam, he was hit by shrapnel that damaged the
left hemisphere of his brain. When asked to tell his
story, he said:
•"My mother died...uh... me... uh fi'tenn. Uh, oh, I
guess six month... my mother pass away. An'uh...
Right hemisphere damage
•Thirty years ago, Lincoln Holmes was in a car accident
that rendered him completely "face blind". "In those
moments when I am suddenly alone, and I don't know
where anybody that I am with is, there can be a surge of
fear, and it is lonely in that sense" When shown a series of
slides of inanimate objects, he is able to identify them
correctly - but finds it completely impossible to recognise a
picture of Marilyn Monroe. Even when shown a picture of
himself, he has to be prompted before he realises he is
staring at his own image. "For me it is a face, it is not my
face, and there is some sense of incompleteness there. So
be it." "When I am asked by people, 'do faces all look the
same?', the answer to that question is 'no' - they don't all
Right hemisphere damage
Poor on visuospatial tasks e.g. Block design
Other findings
•
More often affected after LH
damage:
More often affected after RH
damage:
Language (90%)
Face processing
Reading & writing
Visuospatial tasks
Arithmetic
Melody (“amusica”)
Complex movements
e.g. opening can
Intonation
Limitations
• - Can’t compare R/L hemispheres in same
person
• - Can’t get data on small sub-samples
(e.g. left-handers)
Hemispheric Specialisation:
Methods of Studying
1. Individuals with unilateral lesions
2. WADA Technique
3. "Split Brain" patients
4. Lateralised presentation
(e.g. visual half-field technique)
2. The WADA Technique
• Sodium Amytal
injected into
carotid artery
• Anaesthetises
one hemisphere
• Creates
temporary
unilateral "lesion"
The WADA Technique (cont)

can compare hemispheres in same person

good for studying "unusual" subgroups
• Example: Language localisation in r. and l.
handers
LH
Bilateral
RH
Right handers
96%
0%
4%
Left handers
70%
15%
15%
Total
84%
7%
9%
Hemispheric Specialisation:
Methods of Studying
1. Individuals with unilateral lesions
2. WADA Technique
3. "Split Brain" patients
4. Lateralised presentation
(e.g. visual half-field technique)
3. Split Brain Patients
• Corpus callosum is cut
• LH/RH intact, but don't communicate
The Split Brain Syndrome
•Patients who have undergone this procedure recover to
perform at a normal intellectual and social level. In fact,
they may be totally unaware of having a deficit. One
patient, WJ, was described as "living happily in Downey,
California, with no sense of the enormity of the findings or
for that matter any awareness that he had changed."
•Nevertheless, these patients have some unusual traits….
They sometimes give evidence of having two differing
minds. For example, one patient found his left hand
struggling against his right hand when trying to pull up his
pants in the morning. While the right hand tried to pull them
up, the left was trying to pull them down. On another
Split Brain Studies
• Present stimulus to one hemisphere only:
If ball presented on left
side of screen:
Could P name the item? No
Could he pick the
right object?
Yes
Which hand could he use?
Left right or both?
Stimulus processed by
______
left hemisphere
Left only
Split Brain Studies (cont.)
•
E:
“What was it?”
“What goes on it?"
P:
“I don't know."
E:
“Can you draw it?”
Split Brain Studies (cont.)
Can demonstrate asymmetries in other domains:
•
Other findings
Language Tasks:
• LH can produce and understand all words,
even the most complex sentences
• RH can’t produce speech, but understands
some concrete words, simple sentences
• BUT Beware: split-brain P's may have different
brains premorbidly
Hemispheric Specialisation:
Methods of Studying
1. Individuals with unilateral lesions
2. WADA Technique
3. "Split Brain" patients
4. Lateralised presentation
(e.g. visual half-field technique)
4. Lateralised Presentation in
Normals
 Hemispheres communicate
 BUT first hemisphere to process has
advantage (e.g. accuracy, RT)
 Example: Visual half-field technique
+
CAT
Presentation is brief (< 200msec). Why?
Lateralised Presentation (cont.)
Applications:
 word recognition tasks e.g. lexical decision
 face processing e.g. same-different matching
Can use in other modalities
e.g. dichotic listening
 RH advantage for music
 LH advantage for words
Lateralised Presentation (cont.)
Advantages:
 normals, no pre-existing conditions
 can be performed anywhere, anytime
Drawbacks:
 what do the RT differences actually mean?
Theories of Hemispheric
Specialisation
A. Type of Material: verbal vs. visual
B. Nature of Processing: analytical vs.
holistic
Analytical vs. Holistic theory:
Evidence
•
1. Split-brain studies: visual matching
tasks
Match by visual
similarity
= RH advantage
Target picture
Match by function
= LH advantage
Analytical vs. Holistic theory:
Evidence
• 2.
Normals:
Discrimination of grossly diff. faces = RH
Discrim. of faces differing by one feature = LH
Analytical vs. Holistic theory:
Evidence
• 3. Patients with unilateral brain
damage
"Hierarchical" stimuli:
LH damage (relies on RH)
RH damage (relies on LH)
Alternative models
Dangers of "dichotomies" -> circularity
• Kosslyn: language-driven specialisation:
• * Language specialisation is cause of
asymmetries
• * Other asymmetries reflect categorical nature of
language