Outline for Nov. 21, 2000

1) Announcements:

2) Chapter 15, cont'd.

Chapter 16, Human Communication - pp 496-507 I will not cover in lectures (reading, writing), but you are responsible for these).

4 videos: (2 on memory that we didn't have time for last week), Scientific American Frontiers "Talkin' Babies" (12 min.) and The Mind 2nd ed. #26 "The Bilingual Brain" (7.5 min.), if we have time.

Speech Disorders

Aphasia

• Speech Disturbance - can be mainly in production or mainly in comprehension (Broca's and Wernicke's aphasias, respectively)
• Not the result of lack of motivation for talking or sensory/motor deficits
• Usually associated with left-hemisphere damage

Broca's Aphasia (or motor or production aphasia)

• Damage to left inferior frontal lobe
• Distinct from dysarthria or apraxia of speech
• Evidence for hemispheric lateralization
• Characteristics

Wernicke's Aphasia (sensory or receptive aphasia)

• Word recognition disrupted by damage to superior left temporal gyrus
• Poor speech comprehension

• Evident in nonverbal tasks ('point to object ')
• Cannot repeat statements
• Fluent but meaningless speech ('word salad')
• Lack of use of content words, inappropriate grammar

• Patients are unaware of their deficit
• Speech comprehension deficits

• • Damage to posterior lang. area
  • Can repeat statements (but can't understand!)
  • Suggests dissociation between speech recognition/comprehension

• • Involves conversion of sensory memories, associations, into spoken language. If certain areas of assoc. cortex are damaged (spatial deficit example in text) then certain specific comprehension deficits can result.

• • Information about sounds of words is conveyed by arcuate fasciculus from Wernicke's to Broca's area
  • Patients with disruption exhibit fluent and meaningful speech, good word comprehension, but difficulty repeating words

• • word-finding difficulty in the absence of other deficits
  • Patients exhibit circumlocutions
  • Can be for nouns or verbs

• • Proper nouns - involves temporal pole
  • Common nouns - involves inferior temporal area caudal to pole
  • Verbs - involves area surrounding Broca's area in frontal lobe

The Wernicke-Geschwind Model of Language Processing

• Single most influential theory of language localization
• Spawned a great deal of research, much of which has shown that the model as originally put forth is not an accurate description of what is going on (serial, not parallel, for one thing)

• There were many opponents to the early (Broca, Geschwind) localizationist approach to language, who took a more holistic approach, and they prevailed until Norman Geschwind revived Wernicke's ideas in about 1965.
• 

Evaluation of the W-G model

• Initially based on case studies
• Damage is usually diffuse, not really localized
• Broca's and Wernicke's aphasias rarely if ever occur in their 'pure' forms
• Several studies don't support the model

Effects of removal of brain tissue in specific areas on language-related abilities

Cortical stimulation studies (early - Penfield; later; Ojemann and colleagues). Lots of individual variability in cortical areas subserving language.

a) areas that caused interference with language processing when stimulated electrically - Penfield

b) variability in language representation - Ojemann - numbers are percentage of patients showing interference - many of the sites are outside the classical Broca's and Wernicke's areas.

Prosody

• The melodic aspects of language that help to inject it with emotional meaning
• This aspect of language is generally a right-hemisphere function
• Dichotic-listening studies can determine lateralization for prosody
• Bower-tower-dower-power spoken in 4 different affective tones (16 tokens)

• 2 basic ways to administer the test
• 1-dimensional target (word OR affect)
• 2-dimensional target ("circle 'yes' every time you hear bower spoken in a happy tone of voice"), and analysing false positives

Language processing in the Deaf

• Subserved by the left-hemisphere, in spite of its obvious spatial nature
• Studying acquisition of signing can tell us much about the fundamental nature of language

• Video: Scientific American Frontiers "Talkin' Babies" (12 min.)

Critical Periods in Language Development

• Normally we acquire language without working too hard at it
• The earlier the better
• There's probably an age beyond which we can't acquire normal language skills no matter how hard we work at it (Genie, E.M. are examples)