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Michael Gazzaniga
Helena Yeung and Brian Zhao
Background Born on December 12, 1939 Graduated from Dartmouth College in 1961, received his
Ph.D at Cal Tech in 1964 Worked under Sperry as a his protégé
Sperry was a pioneer of human split-brain research Theories regarding functional lateralism in the brain had
already been established
Findings (split hemispheres) 1967
Experiment on split-brain patients Concluded that split-brain patients
possessed two hemispheres that acted independently
Findings (nonverbal right hemisphere) 1967
Experiment in split-brain patients Flashed a picture of spoon to participant’s right
hemisphere Asked participant to identify the object: participants
generally replied with “I don’t know.” Asked participant to choose the object from a pile of
objects: participants would generally choose correctly.
Concluded that the right hemisphere in split-brain patients was “nonverbal”
Findings (isolated hemispheres) Case study: WJ (epileptic patient with split-
brain) Held apple to WJ’s right eye, and WJ would say, “I
see an apple” Held apple to WJ’s left eye, and WJ would say, “I
don’t see anything,” but would be able to pick out a pictorial representation w/ left hand
Concluded that two hemispheres of the split brain do not communicate with each other
Findings (the interpreter) Gazzaniga labeled the left hemisphere as
“the brain’s interpreter” (1998) Researchers noticed that, when information is
sent to the right-hemisphere to control the left hand, the left hemisphere, when it sees this, interprets this event, and consolidates it with its “ongoing mental monologue”
Gazzaniga proposed that the left hemisphere rationalizes the actions, protecting the holistic nature of the individual’s mind, giving the individual a sense of self
Findings(the “gist” capacity) Experiment: participants were asked to bet
on which of two events would occur, one having an 80% chance of occurring, and the other having a 20% chance of occurring. Instead of choosing the event that repeatedly
occurred, humans often attempted to discern patterns within the frequency of the events
A rat would lose less money than a human through the same process, as they rely more on the right hemisphere
Concluded that right brain takes events and images at face value, while the left brain made theories.
Findings(right hemisphere) Perceptual grouping:
You know that a specific object is at the bottom of a pile, and you go directly for it, without searching
You see a deer in the woods; you can only see parts of the deer, but your brain mentally puts the missing pieces together
Methodology Experiments: Performed on patients who had
undergone split-brain procedures Studied with an apparatus that took advantage of
separate visual fields If a split-brain patient is seated in front of a screen and told
to look at an “X” in the middle of the screen, and if the picture is flashed on the screen too quickly for an eye movement to occur, then everything to the left of the X will go to the right hemisphere. Everything to the right of the X will go to the left hemisphere
Displayed HE*ART on a screen, asked participants to stare at dot When asked what word they saw, participants generally
replied with “ART” When asked to identify the word with their left finger,
participants pointed at “HE”
Case study: WJ (split-brain patient)
Evaluation(findings) Strengths:
Supports concept of lateralization in the brain Provides details regarding the lateralized nature of each
hemisphere Left hemisphere is the “interpreter,” while right hemisphere
deals with perceptual grouping Weaknesses:
Not necessarily applicable to all humans, as experimentation was done on split-brain patients Split-brain is not a naturally occurring affliction
America-centered; cultural biases are not taken into consideration (eg. For language processing in Chinese speakers)
Methodology Strengths:
Experimented on a large population of split-brain patients
Tested both sides of the brain; did not assume control between the hemispheres
Limitations: Used case studies (WJ) that aren’t necessarily
applicable to everyone Extraneous variables not considered (culture,
gender, handedness)
Works Cited Myers, D. G. (2007). Psychology. New York,
NY: Worth Publishers. http://www.abc.net.au/rn/allinthemind/stories/
2008/2276587.htm http://www.downstreamer.com/mindspast.htm
l http://www.psywww.com/intropsych/ch02_hu
man_nervous_system/dual_consciousness_in_split-brain.html