Unformatted text preview: Lecture 20 (March 13th): Language & Lateralization Lecture Outline 1) Evidence for Lateralization (i.e., Hemispheric Specialization) 2) Language: Lesion Studies Demonstrating the Left Hemisphere's Dominance for Language Broca's Aphasia, Wernicke's Aphasia 3) Right Hemisphere's Role in Language 4) Split-Brain Patients and Lateralization 5) Development of Language Lateralization 6) Other Non-Language Lateralizations LATERALIZATION (HEMISPHERIC SPECIALIZATION): Left and Right hemispheres involved in different functions Ways to Study Lateralization: 1) People with Lesions in One Hemisphere 2) Isolate Activity in One Hemisphere Capitalize on Contralateral Input in Sensory Systems Each hemisphere of the brain receives from: - the opposite side of the body (Left-Hand vs. Right-Hand) - the opposite visual field (Left Visual Field (LVF) vs. RVF) ..... but this is not perfect, because the commisures connect the two hemispheres (e.g., Corpus Callosum) So, what would be Perfect for Method (2)? Split Brain Patients (severed Corpus Callosum, come back to later today) LANGUAGE (Humans) Psychologists, Philosophers, Linguists, Cognitive Scientists, Neuroscientists AGE-OLD debate: What constitutes a "language"? - Communication? Gestures? - Intelligence Needed? No, because: "William's Syndrome" - Common View: semantics (symbols, meaning) syntax (structure) Acquisition of LANGUAGE has a critical period The Story of "Genie" (1970, Susan Curtiss, UCLA) Language is (Generally) Left Hemisphere-Dominated LESION (STROKE) STUDIES (Broca & Wernicke, 1800s): Left Hemisphere Lesions -> APHASIA BROCA'S AREA (frontal lobe) BROCA'S APHASIA - Problems in language production - Problems in comprehension of complicated sentences (e.g., "The man was killed by the lion") Because.......trouble with "closed class" words (prepositions and conjunctions), involved in SYNTAX - No trouble with "open class" words (nouns and verbs), involved in SEMANTICS Bottom Line: Semantics okay, Syntax impaired WERNICKE'S AREA (temporal lobe) WERNICKE'S APHASIA - Trouble with comprehension - Can produce fluent speech, but often non-sensible and/or the grammar is incorrect. DEAF Individuals (American Sign Language, ASL) (Bellugi, Salk Institute) Other Aspects of Language Are Right Hemisphere-Dominated Specifically, production and comprehension of prosody The story of "The President's Speech" (Oliver Sachs): LH vs. RH aphasics But for Chinese (tonal) languages, prosody is a LH function! WHY? Aspects of language that are critical for understanding language get "captured" by the LEFT HEMISPHERE (Ma = Horse/Mother/Scold/Hemp) More evidence from Contralateral Input Method: Visual Motion Processing in DEAF vs. HEARING subjects First, remember.... Left Visual Field (LVF) -> RH Right Visual Field (RVF) -> LH In hearing people, visual motion better in LVF (RH) In deaf signers, visual motion better in RVF (LH) If language is (mainly) LH, how can we talk about things that are "experienced" (i.e., received) by the RH? Answer: Connections between hemispheres allow information received by the RH to be sent to the LH (so you can talk about it) 1) corpus callosum (massive) 2) anterior commisure (connects parts of frontal cortex) 3) hippocampal commisure (connects hippocampi) Hippocampal commisure 7-13 msec transmission But what if you are a Split-Brain Patient? Testing Split Brain Patients using Contralateral Input Method (pretty close to Perfect Isolation)
HATBAND x HATBAND x "BAND" x 2) However, can use their Left Hand to feel for the object they saw in their LVF, because both involve the RH. LOTS OF QUESTIONS 1) Can only name the word or item in the RVF (i.e., LH). Testing Split Brain Patients using Contralateral Input Method (con't) 3) What happens when show a movie in the LVF (RH)? MOVIE x How does the "emotional" content of the film get to the LH so you can talk about the emotion? Maybe via the "hippocampal commisure", which is part of the LIMBIC system, and closely tied to the "amygdala". Amygdala Development of Language Lateralization Evidence that LH dominance for Language is INNATE: 1) In 12/14 infants (3 months), the planum temporale (part of Wernicke's area, and involved in language) is twice as large in the LH as compared to the RH (like adults) 2) Babbling infants (6 months) use the Right Side of their mouths more than the Left Side (Petitto et al. 2002). What happens when those same babies SMILE (two slide ahead)? Non-Language Lateralizations The best documented difference (from studies of people with LH vs. RH strokes) (from fMRI studies of intact-brains) LEFT HEMISPHERE: specialized for local visual processing RIGHT HEMISPHERE: specialized for global visual processing What Letter? Draw this house Non-Language Lateralizations (con't) RIGHT HEMISPHERE: "holistic" (last slide), emotional, creative - Emotional Facial Expressions And.... when infants (6 months) SMILE, they use the Left Side of their mouths more than the Right Side (Petitto et al. 2002). - Creativity? Are Left-Handers (RH dominant people) more creative? (controversial) LEFT HEMISPHERE : Analytical, sequential Music? (controversial) ...
View Full Document
- Winter '07
- Biological Psychology, left hemisphere, Lateralization of brain function, Split-brain