Grand Rounds 5/15/2012

Transcription

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2 Grand Rounds 5/15/2012 Department of Neurology P Dr. John Shelley-Tremblay, USA Psychology P I have no financial disclosures P I discuss no medications nore off-label uses of medications

3 An Introduction to the use of Event-related Potentials for the Study of Semantic Memory John Shelley-Tremblay University of South Alabma Dept. Of Psychology

4 Types of memory P Within Long-term memory < Episodic < Semantic P Why study semantic memory? < Tells us about how the majority of our knowledge is stored < May help us to understand and remediate deficits, as in Epilepsy, Alzheimer s, Aphasia, and other disorders with language deficits < Tells us about an important part of the reading process: Our goal is to read for understanding

5 Schematic Representation of the Reader Comprehension processes Integration Text representation with prior context Text representation Meaning and form selection Word representation Word identification Lexical General knowledge Linguistic system Phonology, Syntax, Morphology Lexicon Meaning, Morphology, Syntax, -argument structure -thematic roles Ortographic Units Phonological Units Othographic System Mapping to phonolgy Visual input From Perfetti (2000), Adapted from Levelt (1989)

6 Schematic Representation of the Reader Comprehension processes Integration Text representation with prior context Text representation Meaning and form selection Word representation Word identification Post - Lexical General knowledge Linguistic system Phonology, Syntax, Morphology Lexicon Meaning, Morphology, Syntax, -argument structure -thematic roles Ortographic Units Phonological Units Othographic System Mapping to phonolgy Visual input From Perfetti (2000), Adapted from Levelt (1989)

7 Semantic Priming P Provides clues about the structure and proceses underlying semantic memory P Behavioral priming is the reaction time advantage when responding to a target when it is related to the prime

8 P Common Tasks < Task 1: Word/non-word judgement (lexical decision) < Task 2: Are these words related? (Semantic relatedness) < Task 3: Is prime in same category as target? (Category membership)

9 Example: SOA = 1000ms SOA = Stimulus onset asynchrony 0ms DOCTOR PRIME SOA = 1000ms 1000ms NURSE TARGET Response Priming 0ms TRUCK 1000ms NURSE Response

10 P Behavioral priming is the reaction time advantage when responding to a target when it is related to the prime P Priming effects differ at short (<250 ms), versus long (>750 ms) SOA s

11 < Short SOA: AUTOMATIC PROCESSES Not under conscious control; use no resources Spreading activation (Meyers & Schvanneveldt,1971) Semantic memory as a network, any node must reach threshold in order to be retreived for further processing DOCTOR NURSE

12 < Short SOA: AUTOMATIC PROCESSES Not under conscious control; use no resources Spreading activation (Meyers & Schvanneveldt,1971) Semantic memory as a network, any node must reach threshold in order to be retreived for further processing DOCTOR TRUCK NURSE

13 < Long SOA: CONTROLLED PROCESSES Under conscious control; conflict with other controlled tasks Expectancy generation; although controlled, is thought to be pre-lexical (occurs before target s meaning is accessed); The generation of a possible related set of words after prime presentation. SCALPEL SURGEON DOCTOR HOSPITAL NURSE

14 Seems straightforward...but: P Dagenbach, Carr, & Wilhelmson (1990) XXXXX DOCTOR XXXXX NURSE Response P Masking makes prime identification difficult P When primes are not identifiable, pattern of results changes

15 Negative Priming PIn addition to (+) priming, there is negative priming as well. < RT is slowed for a related prime, in comparison to a neutral (unrelated) baseline XXXXX DOCTOR DOCTOR XXXXX NURSE Slowing Response Response XXXXX TRUCK XXXXX NURSE Response

16 PHow do we account for negative priming? < Dagenbach et al. (1990) posit that prime becomes only weakly activated in lexicon. < Spreading activation would predict NO priming for weak primes, no inhibitory mechanisms DOCTOR < Dagenbach et al. (1990) suggest an alternative mechanism NURSE

17 Attentional Center-Surround Mechanism (CSM) Dagenbach & Carr (1994) < Lexical Level Effect (+) ROCK DOCTOR (-) NURSE

18 Retrospective Prime Clarification Theory (RPC) Kahan (1999) Pwhen a masked word is presented that is difficult to identify P then the target will be used to aid in the identification of the prime P A version of semantic matching; occurs after meaning of prime and target are processed

19 PTask: Is nurse a word? (*prime unretreivable) Unrelated NURSE DOCTOR? NO HOSPITAL?NO Generate possible matches (few) Response = NO End search Relatively fast Related + NURSE HOSPITAL? NO SCALPEL? NO BED PAN? NO NO Generate possible matches (many) Relatively slow

20 PHow does RPC account for negative priming? + NURSE PWhen prime is unclear, S uses target to aid in its retrieval P Subject matches task-relevant codes of the target to those of the prime P Greater number of partial matches resulting in a slow down in decision time

21 P Competing Hypotheses: < RPC: negative priming due delay in matching process: POST LEXICAL < CSM: negative priming due to inhibition of target s level of activation: LEXICAL

22 P Competing Hypotheses: < RPC: negative priming due delay in matching process: POST LEXICAL < CSM: negative priming due to inhibition of target s level of activation: LEXICAL P RT cannot easily differentiate these processes PEvent-related potentials provide a window into the sub-stages of mental processes

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24 Event-related Potential (ERP) P Necessary Components < Stimulus delivery device < Electrode Array Receives brain waves < Amplifier Magnifies tiny (~5-100 υv) signals < EEG recording computer W/ A to D sampling card < Post-recording software Turns EEG into ERP s SUBJECT! X 1,Y 1 X 2,Y 2 X 3,Y 3 X 4,Y 4

25 ERP Methods P Collection of continuous EEG

26 P From multiple points on the scalp NOSE

27 ERP Methods TREE DOG CAT DOCTOR NURSE (Preceded by SHRUB ) Functionally equivalent stimuli are combined.

28 TREE CAT TREE NURSE CAT NURSE Stimuli of the same type are combined (related with related) (unrelated with unrelated)

29 P Individual segments are sorted by stimulus type and averaged P Event-related activity becomes magnified (because its time-locked), while noise is reduced.

30 The N400 Component PThe N400 is a late negative component, elicited by words and legal non-words, which is smaller for words which are semantically primed than for those which are not (Bentin, McCarthy, & Wood 1985; Kutas & Hillyard, 1989). P First discovered in complete sentences, such as:

31 +3.5µV She spread the warm bread with butter. N400 Response Congruent Incongruent -3.5µV butter 1000ms

32 +3.5µV She spread the warm bread with socks. N400 Response Congruent Incongruent -3.5µV butter socks 1000ms

33 +3.5µV Priming N400 Response Congruent Incongruent -3.5µV 1000ms

34 P N400 also elicited by single words, and is sensitive to priming by a single prime word PDOCTOR - NURSE (Primed) PTRUCK - NURSE (Unprimed)

35 What does the presence of the N400 component tell us? (I.E., what is its functional significance?) PN400 reflects lexical/semantic processing. < N400 priming occurs at short SOA (Boddy,1986) < N400 priming when word is masked to below recognition threshold (Deacon, Hewitt, Yang, & Nagata,2000) < N400 priming when prime and target are being actively ignored (Shelley-Tremblay & Deacon, in preparation)

36 ERP Evidence for an Attentional Center-surround Mechanism John Shelley-Tremblay & Diana Deacon, PhD City University of New York PHow can we produce weakly activated primes without the trouble of masking? Barnhardt, Glisky, Polster, & Elam (1996) PExperimental Design < Training Phase: Learn new words (very rare) < ERP Phase: new (rare) words serve as primes < Final Recognition Test

37 PTraining Phase < Subjects presented with 104 novel words < One at a time for 7 seconds < Subjects train until 50% recal criterion Ready?

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39 PFactors involved Priming Primed Unprimed Claver-Rock Associate Claver-Gossip Synomym Claver-Chat CLAVER CHAT + CLAVER ROCK

40 P HYPOTHESES < LH will show priming for synonyms, but reverse priming for associates If N400 negative priming occurs (lexical level), CSM is supported LH RH < Lexical Level Effect CLAVER (+) CLAVER CHAT (-) CHAT ROCK GOSSIP ROCK GOSSIP < RH will show priming for associates, and may show priming for synonyms (NO INHIBITION)

41 LH Synonyms N400 F3 FZ F4 T3 C3 CZ C4 T4 T5 P3 PZ P4 T6 Primed Unprimed O1 OZ O2 +3.5µV 450 ms

42 LH Associates N400 F3 FZ F4 T3 C3 CZ C4 T4 T5 P3 PZ P4 T6 Primed Unprimed O1 OZ O2 +3.5µV 450 ms

43 HEOG RH Associates N400 F3 FZ F4 VEOG T3 C3 CZ C4 T4 T5 P3 PZ P4 T6 Primed Unprimed O1 OZ O2 +3.5µV 450 ms

44 RH Synonyms N400 F3 FZ F4 T3 C3 CZ C4 T4 T5 P3 PZ P4 T6 Primed Unprimed O1 OZ O2 +3.5µV 450 ms

45 Conclusions P N400 shows LH priming for synonyms (center) P N400 shows LH reverse priming for associates (surround) P In conjunction, this dissociation supports existence of CSM in LH P RH associative priming suggests a rich language network with qualitative differences from LH P *Excellent learners didn t show reverse priming... Does it activate and dissipate very rapidly, or do excellent learners lack this mechanism? Would adoption of good learners strategies lead to a dissapearance of reverse priming?

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47 Why ERP s How do ERP s complement RT as a cognitive measure? P Provides alternative source of evidence.

48 P Gives clues about the neural substrates of cognitive processes. N400 Subtraction wave for LH Associates What areas of scalp reveal most electrical activity?

49 P Allows for fine-grained analysis of time course of proposed cognitive operations.

50 P Can be combined with neuroimaging to determine sources of brain activity. Priming Effect: Voltage Map Unprimed Primed

51 Clinical Application Visual Evoked Potentian (VEP) Origins of Dyslexia Neurobiological Origin Impairment of Visual System Deficit in Magnocellular Pathway (M-Pathway) Dyslexia

52 M-Pathway in Visual System P One of three pathways in visual system P motion detection pathway P originates from the rod receptors located on the retina P very sensitive to low contrast and low spatial frequencies

53 Area MT

54 PATH Training P Uses a series of grayscale stripes that differ in width with each trial. P A target area in the shape of a fish is located in the middle of the background stripes. P The stripes in the fish move left or right; the child must discriminate which direction the stripes are moving in each trial

55 VEP RESULTS F V 0. 0 F V Electrode: O Electrode: OZ ms Time 1 VEP.avg Time 2 VEP.avg ms Electrode: O2 F V 0. 0 F V ms Electrode: PO2

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58 Questions?