Ppt Chap 14

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 is connected to the contralateral (opposite) side of the body.– Example: skin receptors and muscles on

the right side of the body are connected to the left hemisphere

– Each hemisphere processes visual information from the opposite side of the world.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.

• 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.


• 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 better performance on some tasks

compared split-brain people.


• The left hemisphere is dominant for speech in 95% of right-handed people.

• Left-handers are more variable• Most left-handers have left-hemisphere• Some have right-hemisphere or mixed-

dominance for speech.• also reversed for spatial perception• Research on hemisphere dominance should

not be over-emphasized– Behaviors require use of both

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.


• 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.


• Bonobos or pygmy chimpanzees resemble humans more than other primates.

• show better comprehension of human language:– Understand more than they can produce.– Use symbols/names to describe objects.– Request items not seen.– Use symbols to describe past events.– Make original, creative requests.


• Explanations include:• Perhaps bonobos have greater language

potential than other chimpanzees• Language training began early with subjects• Subjects were also allowed to learn through

observation and imitation in addition to formal training


• Non-primates also display some aspects of spoken language.

• The African gray parrot show a great ability for imitating sounds and also using sounds meaningfully.– Example: Alex the gray parrot.


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.• Indicate that language evolved from a

precursor found in other species• Illustrate the ambiguity of our concept of

language.– Creates demand for more precise

definition.


• 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 a brain specialization.”


• 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.


• 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.


• 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.


• Research suggests a sensitive period exists for the learning of language.– No early language exposure can lead to

permanent impairment• Learning of a second language differs as a

function of age:– Children excel at learning pronunciation

and unfamiliar aspects of grammar.• No sharp cutoff exist for second language

learning.– Earlier the better


• 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.


• 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.


• Broca’s aphasia/nonfluent aphasia refers to serious impairment in language production, usually due to brain damage.

• Also have comprehension deficits when sentence structure is complex

• Omission of most pronouns, prepositions, conjunctions, auxiliary verbs, tense and number endings during speech production.

• Difficulty understanding the same kinds of words they omit (prepositions and conjunctions).


• Broca’s aphasia is usually accompanied by comprehension deficits when: – The sentence meaning depends on

prepositions, word endings or unusual word order.

• Broca’s area thus seems to be critical for the understanding of some, but not all, aspects of grammar.


• Wernicke’s area is an area of the brain located near the auditory part of the cerebral cortex.

• Wernicke’s/ fluent aphasia is characterized by impaired language comprehension and the impaired ability to remember the names of objects

• Sometimes called “fluent aphasia” because the person can still speak smoothly.

• Recognition of items is often not impaired; ability to find word is impaired.


• 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).

Broca’s Aphasia and Wernicke’s Aphasia

Type Pronunciation Content of Speech

Comprehension

Broca’s aphasia

Poor Mostly nouns and verbs, omits prepositions and other grammatical connectives

Impaired if the meaning depends on complex grammar

Wernicke’s aphasia

Unimpaired Grammatical but often nonsensical; has trouble finding the right word, especially names of objects

Seriously impaired


• Bilingual speakers process multiple languages in the same areas of the brain.

• Languages are not kept in separate areas• Language areas in temporal and frontal

cortex grow thicker than average in those that are fluent in two languages from early childhood.


• Bilinguals (con’t)• Those that are more adept at one language,

show greater brain activity for the second language.

• Switching between languages activates the frontal cortex, temporal cortex and basal ganglia

• Brain must work hard to prime one set of words while inhibiting another


• No other species develops music to the same extent

• Has many parallels to language• Broca’s area strongly activated • Suggest we use language areas of the brain

when we compose music.


• Dyslexia is a specific impairment of reading in a person with adequate vision and adequate skills in other academic areas.– More common in boys.– Linked to at least four genes that produce

deficits in cognition or hearing


• In some cases, dyslexia is associated with mild abnormality in various brain structures.– More likely to have a bilateral symmetrical

cerebral cortex.– Less arousal in the parietal and temporal

cortex while reading


• Research and literature is often confusing:• Different people have different types of

reading problems• Small number have impaired control of eye

movements • Most have auditory problems


• Some researchers distinguish:• “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.


• 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


• Most people with dyslexia have auditory problems

• Brain scans show less than normal response to speech sounds

• Trouble detecting the temporal order of sounds

• But not just impaired hearing• Perhaps connecting vision to sound or paying

attention to different aspects of sound.


• 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.

Attention

• Conscious is a difficult concept to define• Researchers use the operational definition:• “If a person reports the presence of one

stimulus but can not report the presence of the second, he or she was conscious of the first and not the second”

• Almost synonymous with attention

Attention

• Psychologist have noted the phenomenon of inattentional blindness:

• Of all that your eyes see, you are conscious of only those few things to which you direct your attention

• While observing a complex scene, you will not notice if something changes slowly

Attention

• Exploration of which types of brain activity are conscious are to present a single stimulus and differentiate brain activity between the occasions with and without consciousness.

• Stimulus initially activates primary visual cortex in both conditions

• More strongly activated in the conscious condition and activity spreads to several additional areas.

Attention

• Consciousness depends upon the amount of brain activity.

• Increasing attention to a stimulus also increases brain activity.

• A conscious stimulus also induces a precise synchrony of responses in neurons over various areas of the brain

Attention

• Binocular rivalry are slow and gradual shifts of the eye sweeping form one side to another.

• Stimulus seen by each eye evokes a particular pattern of brain responses.

• Research shows that switching to each stimulus is accompanied by a shift in a pattern of activity over a large portion of the brain.

Attention

• Research suggest consciousness is a threshold phenomenon

• If a stimulus activates enough neurons to a sufficient extent, the activity reverberates, magnifies, and extends over much of the brain.

• If a stimulus fails to reach that level, the pattern fades away.

Attention

• Meaningful stimuli capture our attention faster than meaningless stimuli.

• Somehow brain has to know that it was meaningful before it became conscious.

• Indicates: • Much of brain activity is unconscious• Subtle effects on behavior by unconscious

stimuli can exist.

Attention

• Delays exist between an event and our consciousness of it.

• Phi phenomenon occurs when we see a dot in one position alternating with a similar dot nearby

• Appears as if the dot is moving back and forth.

• Reveals that perceptions of events after can also alter changes in event that occurred before.

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.

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.

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.

Ppt Chap 14

Technology

Transcript of Ppt Chap 14