Download MODULE 2.5 The Divided Brain: Specialization of Function

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Chapter 2 Biological Foundations of Behavior
MODU LE 2.5
The Divided Brain: Specialization of Function
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What are the major differences between the left and right hemispheres?
What determines handedness?
What can we learn about brain lateralization from studies of “split-brain” patients?
What are the major causes of brain damage, and what effects do they have on
psychological functioning?
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Concept 2.27
In most people, the left hemisphere is
specialized for use of language and
logical analysis, while the right hemisphere is specialized for spatial processing and other nonverbal tasks.
Lateralization of Brain Function The
right hemisphere is dominant for spatial
tasks, such as solving jigsaw puzzles,
whereas the left hemisphere is dominant
for verbal tasks, such as speaking, reading,
and writing.
f you stub your left toe, cells in your right parietal lobe will “light up,” producing sensations of pain. Conversely, a blow to your right toe will register in
your left parietal lobe. This is because the sensory cortex in each hemisphere is
connected to sensory receptors on the opposite sides of the body. Likewise, the
motor cortex in your right frontal lobe controls the movements of the left side
of your body, and vice versa. Thus, if we were to stimulate your left motor cortex in a certain spot, the fingers on your right hand would involuntarily contract. As we see next, evidence indicates that the right and left hemispheres are
also specialized for certain types of functions.
The Brain at Work: Lateralization and Integration
The term lateralization refers to the division of functions between the right and
left hemispheres (see Concept Chart 2.5). Generally speaking, the left hemisphere
in most people appears to be dominant for language abilities—speaking, reading,
and writing (Blakeslee, 1996; Gazzaniga, 1999). The left hemisphere also appears
to be dominant for tasks requiring logical analysis, problem solving, and mathematical computations. The right hemisphere in most people appears to be dominant for nonverbal processing, such as understanding spatial relationships (e.g.,
piecing together puzzles, arranging blocks to match designs, reading maps), recognizing faces, interpreting people’s gestures and facial expressions, perceiving
and expressing emotion, and appreciating music and art.
Despite such differences, people are not “left-brained” or “right-brained”
(Gazzaniga, 1995; Hellige, 1993). The functions of the hemispheres largely overlap, and messages rapidly zap back and forth across the corpus callosum, the bundle of nerve fibers that connects the hemispheres. In fact, though one hemisphere
or the other may be dominant for a particular task, both hemispheres share the
work in performing most tasks.
Language dominance is associated with handedness. For about 95 percent of
right-handed people and even for about 70 percent of left-handed people, the left
hemisphere is dominant for language functions (Damasio & Damasio, 1992;
Pinker, 1994; Springer & Deutsch, 1993). For about 15 percent of left-handed people, the right hemisphere is dominant for language functions. The other 15 percent of left-handers show patterns of mixed dominance.
CONCEPT CHART 2.5
Lateralization of Brain Functions
Areas of Left-Hemisphere Dominance
Areas of Right-Hemisphere Dominance
Verbal functions (for right-handers and most left-handers), including
spoken and written use of language, as well as logical analysis, problem
solving, and mathematical computation
Nonverbal functions, including understanding spatial relationships (as
presented, e.g., in jigsaw puzzles or maps), recognizing faces and interpreting gestures, perceiving and expressing emotion, and appreciating
music and art