Chapter 14:
Cognitive Functions
Lateralization of Function
• Lateralization of function refers to the idea
that each hemisphere of the brain is
specialized for different functions.
• Each hemispheres controls the contralateral
(opposite) side of the body.
– Example: skin receptors and muscles
mainly on the right side of the body.
– Each hemisphere sees the opposite side of
the world.
Lateralization of Function
• The left and right hemisphere exchange
information primarily through a set of axons
called the corpus callosum.
• Other areas that exchange information
include:
– The anterior commissure.
– The hippocampal commissure.
– A few other small commissures.
• Information crosses to the other hemisphere
with only a brief delay.
Fig. 14-2, p. 418
Lateralization of Function
• The two hemispheres are not mirror images
of each other.
• Division of labor between the two
hemispheres is known as lateralization.
– In most humans the left side is specialized
for language.
• The corpus callosum allows each hemisphere
of the brain access to information from both
sides.
Lateralization of Function
• Each hemisphere of the brain gets input from
the opposite half of the visual world.
• The visual field is what is visible at any
moment.
• Light from the right half of the visual field
shines into the left half of both retinas.
• Light from the left visual field shines onto the
right half of both retinas.
Lateralization of Function
• The left half of each retina connects to the left
hemisphere.
• The right half of each retina connects to the
right hemisphere.
• Half of the axons from each eye cross to the
opposite side of the brain at the optic chiasm.
• The auditory system is arranged differently in
that each ear sends the information to both
sides of the brain.
Fig. 14-3a, p. 419
Lateralization of Function
• Damage to the corpus callosum interferes
with the exchange of information between
hemispheres.
• Epilepsy is a condition characterized by
repeated episodes of excessive synchronized
neural activity.
– Mainly due to decreased release of the
inhibitory neurotransmitter GABA.
• Physicians once cut the corpus callosum to
prevent the seizure from spreading to the
opposite side of the body.
Lateralization of Function
• People who have undergone surgery to the
corpus callosum are referred to as split-brain
people.
• Spit brain people maintain normal intellect
and motivation but they tend to:
– Use hands independently in a way others
cannot.
– Respond differently to stimuli presented to
only one side of the body.
Fig. 14-4, p. 420
Lateralization of Function
• Sperry (1974) revealed subtle behavioral
differences for spilt brain people.
• Because the left side of the brain is dominant
for language in most people, most split brain
people:
– Have difficulty naming objects briefly
viewed in the left visual field.
• A small amount of information can still be
transferred via several smaller commissures.
Fig. 14-5, p. 422
Lateralization of Function
• Immediately after surgery, each hemisphere
can only quickly and accurately respond to
information that reaches it directly.
– Smaller commissures allow a slower
response.
• The brain later learns use the smaller
connections:
• Difficulty integrating information between both
remains.
Fig. 14-6, p. 423
Lateralization of Function
• Right hemisphere is better at perceiving
emotions.
• Damage to parts of the right hemisphere
causes difficulty perceiving other’s emotions,
failure to understand humor and sarcasm,
and a monotone voice.
• Left hemisphere damage increases ability to
accurately judge emotion.
– Associated with decreased interference
from the left hemispheres.
Lateralization of Function
• The right hemisphere is also better at
comprehending spatial relationships.
• In general, the left hemisphere seems to
focus more on visual details, and the right
hemisphere focuses more on visual patterns.
Lateralization of Function
• Some anatomical differences exist between
the hemispheres of the brain.
• The planum temporale is an area of the
temporal cortex that is larger in the left
hemisphere in 65% of people.
– Difference are slightly greater for people
who are strongly right handed.
• MRI studies indicate that the a big difference
in the ratio of left to right planum temporale is
related to increased language performance.
Fig. 14-9, p. 425
Lateralization of Function
• Damage to left hemisphere often results in
language deficiencies.
• Left side seems to be specialized for
language from the very beginning in most
people.
• The corpus callosum matures gradually
through the first 5 to 10 years.
– Thus, young children have difficulty
comparing information from the left and
right hand.
Lateralization of Function
• Being born with a condition where the corpus
callosum does not completely develop results
in extra development of the following:
– Anterior commissure - connects the
anterior parts of the cerebral cortex.
– Hippocampal commissure - connects the
left and right hippocampus.
• Allows performance on some tasks that
differs from split-brain people.
Lateralization of Function
• The left hemisphere is dominant for speech in
95% of right-handed people.
• Most left-handers have left-hemisphere or
mixed-dominance for speech.
– Few people have strong right hemisphere
dominance.
Lateralization of Function
• Recovery of language after damage to the
brain varies.
• Age affects extent of recovery.
– Brain is more plastic at an early age.
• Right hemisphere reorganizes to serve some
of the left-hemisphere function.
Lateralization of Function
• Rasmussen’s encephalopathy is a rare
condition in which the immune system initially
attacks the glia and then the neurons of one
hemispheres of the brain.
– Usually begins in childhood or
adolescence.
• Surgeons eventually remove or disconnect
the side of the damaged brain.
• Language recovers slowly but substantially.
– Slow deterioration allows the other side of
the brain to compensate and reorganize.
Lateralization of Function
• Language recovery after brain damage is
also influenced by how language was initially
lateralized for the given person.
• Individuals with partial representation of
language in both hemispheres recover better
than those with language dominance in one
hemisphere.
Evolution and Physiology of Language
• Human language is a complex form of
communication.
• Compared to other species, human language
has high productivity.
– Productivity - the ability to produce new
signals to represent new ideas.
Evolution and Physiology of Language
• Human language is most likely a modification
of a behavior also found in other species.
• Chimpanzees use language but it differs from
humans:
– Seldom use symbols in new original
combinations.
– Use of symbols lacks productivity.
– Use of symbols is primarily used to request
and not describe.
– Production of requests is better than
understanding other’s requests.
Evolution and Physiology of Language
• Bonobos or pygmy chimpanzees show an
increased comprehension of human
language:
– Understand more than they can produce.
– Use symbols and names to describe
objects.
– Request items not seen.
– Use symbols to describe past events.
– Make original, creative requests.
Lateralization of Function
• Non-primates also display some aspects of
spoken language.
• Elephants imitate sounds they hear, including
the vocalizations of other elephants.
• Dolphins respond to gestures and sounds.
• The African gray parrot show a great ability
for imitating sounds and also using sounds
meaningfully.
– Example: Alex the gray parrot.
Evolution and Physiology of Language
Studies of nonhuman language abilities:
• Give insights to how best to teach language
to those who do not learn it easily.
– Examples: Brain damaged people or
children with autism.
• Illustrate the ambiguity of our concept of
language.
– Allows for more precise definition.
Evolution and Physiology of Language
•
Two categories of theories attempt to
explain the human ability to learn language
more easily than other species.
1. “Language evolved as a by-product of
overall brain development.”
2. “Language evolved as an extra part of the
brain.”
Evolution and Physiology of Language
•
Problems associated with the “language as
a by-product of increased intelligence”
theory:
1. People with a full-size brain and normal
overall intelligence can show severe
language deficits.
2. People with impaired intelligence can
have normal language skills.
• Williams syndrome characterized by
metal retardation but skillful use of
language.
Fig. 14-14, p. 433
Evolution and Physiology of Language
• Evidence suggesting language evolved as an
extra brain module specialization includes:
– Language acquisition device is a built in
mechanism for acquiring language.
• Evidence comes from the ease at which
most children develop language.
– Chomsky (1980) further suggests the
poverty of stimulus argument: children do
not hear many examples of some of the
grammatical structures they acquire.
Evolution and Physiology of Language
• Most researchers agree that humans have a
specially evolved “something” that enables
them to learn language easily.
– Certain brain areas are indeed necessary
for language.
– But same areas are also necessary for
other tasks (memory and music
perception).
• Exactly how humans evolved language is
unknown but is perhaps due to the pressure
for social interaction.
Evolution and Physiology of Language
• Research suggests a critical period exists for
the learning of language.
• Learning of a second language differs as a
function of age:
– Children are better at learning
pronunciation and unfamiliar aspects of
grammar.
• No sharp cutoff exist for second language
learning.
– Adults learn a second-language vocabulary
better.
Evolution and Physiology of Language
• Rare cases of children not exposed to
language indicates limited ability to learn
language later.
• Deaf children unable to learn spoken
language and not given the opportunity to
learn sign language while young reveals:
– Little development of skill at any language
later.
– Early exposure to some language
increases ability to learn another language
later.
Evolution and Physiology of Language
• Most knowledge of brain mechanisms of
language come from the study of people with
brain damage:
– Broca’s area is a part of the frontal lobe of
the left cerebral cortex near the motor
cortex.
• Damage results in some language
disability.
– Aphasia refers to a condition in which there
is severe language impairment.
Evolution and Physiology of Language
• Broca’s aphasia/nonfluent aphasia refers to
serious impairment in language production,
usually due to brain damage.
• Omission of most pronouns, prepositions,
conjunctions, auxiliary verbs, tense and
number endings during speech production.
• People with Broca's aphasia have trouble
understanding the same kinds of words they
omit (prepositions and conjunctions).
Evolution and Physiology of Language
• Broca’s aphasia is usually accompanied by
comprehension deficits when:
– The sentence meaning depends on
prepositions, word endings or unusual
word order.
– Sentence structure is complicated.
• Broca’s area thus seems to be critical for the
understanding of some, but not all, aspects of
grammar.
Fig. 14-15, p. 435
Fig. 14-16, p. 436
Evolution and Physiology of Language
• Wernicke’s area is an area of the brain
located near the auditory part of the cerebral
cortex.
• Wernicke’s aphasia is characterized by the
impaired ability to remember the names of
objects and also impaired language
comprehension.
– Sometimes called “fluent aphasia” because
the person can still speak smoothly.
• Recognition of items is often not impaired;
ability to find word is impaired.
Evolution and Physiology of Language
•
Typical characteristics of Wernicke’s
aphasia include:
1. Articulate speech / fluent speech except
with pauses to find the right word.
2. Difficulty finding the right word - anomia
refers to the difficulty recalling the name
of objects.
3. Poor language comprehension - difficulty
understanding spoken and written speech
(especially nouns and verbs).
Table 14-1, p. 438
Evolution and Physiology of Language
• Dyslexia is a specific impairment of reading in
a person with adequate vision and adequate
skills in other academic areas.
– More common in boys.
– Research suggests a genetic influence.
Evolution and Physiology of Language
• In some cases, dyslexia is associated with
mild abnormality in the structures of various
brain areas.
– More likely to have a bilateral symmetrical
cerebral cortex.
– Language–related areas in the right
hemisphere are larger in some.
– Weak connections exist among other
areas.
Evolution and Physiology of Language
• Different kinds of dyslexics have different
reading problems.
• “Dysphonic dyslexics” have trouble sounding
out words.
– Attempt to remember them as a whole.
• “Dyseidetic dyslexics” fail to recognize a word
as a whole.
– Read slowly and have particular trouble
with irregularly spelled words.
Evolution and Physiology of Language
• Most severe cases of “dyseidetic dyslexia”
result from brain damage that restricts the
field of vision.
• Characterized by the following:
– only seeing one letter a time.
– short eye movements.
– very slow reading.
– difficulty with long words.
Evolution and Physiology of Language
• One hypothesis to explain dyslexia
emphasizes a hearing impairment rather than
visual impairment.
– Less than normal response to speech
sounds in the brain.
– Lack of ability to pay close attention to
sounds.
Evolution and Physiology of Language
• Another hypothesis to explain dyslexia is
connecting vision to sound.
• Brain scans indicate that reading strongly
activates areas of the left temporal and
parietal cortex for most people.
– Areas are associated with connecting
visual and auditory information.
• Only weakly activated for people with
dyslexia.
Evolution and Physiology of Language
• A final hypothesis relates dyslexia to
differences in attention.
• Reading requires the shifting of attention.
• People with dyslexia do not shift their
attention in the same way.
• Effective treatment may be for dyslexics to
focus on one word at a time.
Fig. 14-17, p. 440
Attention
• Attention is a multi-dimensional process and
related to consciousness.
• Attention relates to increased brain activity in
the areas responsive to a stimulus.
• Stimuli destined to become conscious or
unconscious produce about the same brain
activity in the first 200-250 milliseconds.
• In the next few milliseconds, the brain
enhances activity for stimuli that become
conscious.
Attention
• Enhancement of activity can be due to
intensity of the stimulus, similarity to past
important stimuli, or other features of the
stimulus itself.
• Enhancement of activity can also be due to
shifting of attention.
• Research suggests that attention pertains
more to the enhancing of relevant activity
than inhibiting irrelevant activity.
Attention
• “Inattention” or “neglect” is the opposite of
attention.
• Spatial neglect is a tendency to ignore the left
side of the body and its surroundings or the
left side of objects.
– Often associated with damage to the right
hemisphere of the brain.
Attention
• Exact location of the damage to the right
hemisphere can affect the details of what the
person neglects.
– Damage to the inferior part of the right
parietal cortex leads to the neglect of
everything to the left of their own body.
– Damage to the superior temporal cortex
neglect the left side of objects, regardless
of location.
Fig. 14-19, p. 444
Attention
• Problems of neglect are associated with
attention and not sensation.
• Someone with neglect can see an entire letter
enough to say what it is.
• The same person ignores the left half when
asked to cross out all the letters that compose
a word.
Attention
• Several procedures can increase attention to
the neglected side:
– telling the person to pay attention to the left
side.
– telling the person to look left while feeling
an object with the left hand or hearing a
sound from the left side.
• A touch stimulus briefly increases attention to
one side of the body or the other.
• Crossing of the hands in front of the body
also decreases neglect to the left side.
Fig. 14-20, p. 444
Attention
• Many patients with spatial neglect also have
deficits with spatial working memory and with
shifting attention, even when location is
irrelevant.
• Thus, problems associated with neglect
extend to many aspect of attention rather
than simply the left-right dimension.
Attention
• Attention-Deficit Hyperactivity Disorder
(ADHD) is characterized by the following:
– Attention deficits (distractibility).
– Hyperactivity (fidgetiness).
– Impulsiveness.
– Mood swings.
– Short temper.
– High sensitivity to stress.
– Impaired ability to make and follow plans.
Attention
• ADHD affects social behavior and school
performance.
• Some have occupational problems and
antisocial behaviors in adulthood.
• Estimates range from 3%-10% of children
• Twice or three times as likely in males.
• Research is complicated by the ability to
make reliable diagnoses.
Attention
•
Three example of tasks which people with
ADHD differ:
1. “The choice delay task” - more likely than
others to choose a smaller but quicker
reward (impulsiveness).
2. “The stop signal task” - difficulty inhibiting
behaviors.
3. “The attentional blink task” - indicates
trouble controlling attention and difficulty
shifting it when needed.
Attention
• Twin studies suggest fairly high heritability
(Thapar et al., 2003).
– Several genes have been identified which
influence performance on tests of attention.
• ADHD probably depends on multiple genes
as well as environmental influences.
• Probability of ADHD is elevated among
children of women who smoked cigarettes
during pregnancy.
Attention
• Structural brain differences include a smaller
than average prefrontal cortex and
cerebellum.
– Cerebellar dysfunction is known to be
associated with difficulty switching
attention.
• Structural differences in the brain are small
and inconsistent between cases.
– Brain scans do not provide reliable results
for diagnoses.
Attention
• The most common treatment for ADHD is
stimulant drugs or amphetamines.
– Example: methylphenidate/Ritalin.
• Stimulant drugs increase attentiveness,
improve school performance and social
relationships, and decrease impulsiveness.
• Also improve scores on laboratory tests, such
as the “stop signal task”.
• Justifying the benefits derived from taking the
drugs is a complex and controversial issue.
Attention
• Amphetamines and methylphenidate increase
the availability of dopamine to the
postsynaptic receptors.
• Maximum benefit occurs 1 hour after
ingestion and benefits last for a few hours.
• Several studies have found that stimulant
drugs enhance certain aspects of learning
and attention for all people, not just those
with ADHD.
Attention
• Behavioral techniques are available as
supplements or substitutes for stimulant
drugs:
– Reduce distractions.
– Use lists, calendars, and other
organizational techniques.
– Practice strategies to pace yourself.
– Learn to relax; tension and stress can
magnify attention deficits.