Chapter 14: Cognitive Functions

1. Chapter 14:Cognitive Functions

2. 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.

3. 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.

5. 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.

6. 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.

7. 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.

9. 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.

10. 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.

12. 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.

14. 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.

16. 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.

18. 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.

20. 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.

22. 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.

23. Lateralization of Function • 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.

24. 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 better performance on some tasks compared split-brain people.

25. Lateralization of Function • 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

26. 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.

27. 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.

29. Evolution and Physiology of Language • 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.

31. Evolution and Physiology of Language • 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

32. Lateralization of Function • 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.

35. 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. • 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.

36. Evolution and Physiology of Language • Two categories of theories attempt to explain the human ability to learn language more easily than other species. • “Language evolved as a by-product of overall brain development.” • “Language evolved as a brain specialization.”

37. Evolution and Physiology of Language • Problems associated with the “language as a by-product of increased intelligence” theory: • People with a full-size brain and normal overall intelligence can show severe language deficits. • People with impaired intelligence can have normal language skills. • Williams syndrome characterized by metal retardation but skillful use of language.

39. 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.

40. 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.

41. Evolution and Physiology of Language • 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

42. 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.

43. 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.

45. Evolution and Physiology of Language • 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).

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

48. 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/ 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.

49. Evolution and Physiology of Language • Typical characteristics of Wernicke’s aphasia include: • Articulate speech / fluent speech except with pauses to find the right word. • Difficulty finding the right word - anomia refers to the difficulty recalling the name of objects. • Poor language comprehension - difficulty understanding spoken and written speech (especially nouns and verbs).

50. Broca’s Aphasia and Wernicke’s Aphasia