Transcript Slide 1

Hemispheric Asymmetries In False Recognition May Depend on Associative Strength
Cathy S. Robinson & Christine Chiarello
University of California, Riverside
Introduction
Semantic Encoding
The cerebral hemispheres process language in a qualitatively different manner,
with hemisphere advantages shown under specific circumstances and
semantic relationships (Chiarello, 1998).
• The left hemisphere (LH) processes meaning with quicker, more focused
selection and integration processes when meaning is contextually close.
• The right hemisphere (RH) processes in a broader, more diffuse manner,
activating distantly-related meanings. Comprehenders may be unaware of
broader meanings, due to poor RH integration and selection (Beeman,
1998).
False Memory Paradigm
The Deese, Roediger, & McDermott task (DRM; 1995) is ideal for looking at
the consequences of one’s general knowledge of word meaning on memory.
• False memory = person remembers something that never happened.
• Task designed to examine how preexisting knowledge influences a person’s
memory for new information. Specifically, examining how errors occur.
DRM Task
• Study phase: participants study a list of words all associated to a critical
word that is not studied (e.g., BOOK: text, library, novel, author, etc.)
• Recognition test: participants make forced choice (old/new) for studied,
critical, and unrelated words, with a high probability of false recognizing the
unstudied critical word.
• During study: previous knowledge makes it more likely that people will
include information that was not part of the event, i.e., memorizing the
related words.
False Memory & Divided Visual Field Studies
Westerberg & Marsolek (2003), & Ito (2001) examined false memory with
two hemispheric memory theories and found:
•more false memory in the RH than in the LH.
•greater accuracy for studied words in the LH.
•Because of greater accuracy in the LH, Ito attributed his findings to the
RH processing in a more diffuse manner and the LH employing a
quicker, more focused selection process.
Experiment Design & Predictions
Design
Lateralized false-memory task with three conditions: list backwards
association strength (strong, weak), visual field (rvf-LH, lvf-RH), and
word type (critical, studied, unrelated).
Predictions
In setting up experimental conditions with relatively strong and weak strength
relationships between the critical words and their list words, it is expected
that:
Strong list hemispheric asymmetries:
•Critical words: more false recognition in LH than the RH
•Studied words: increased correct recognition in the LH than in the RH.
Weak list hemispheric asymmetries:
•Critical words: more false recognition in the RH than the LH.
•Studied words: more correct recognition in the RH than the LH.
Strong List (M = .447)
Weak List (M = .051)
Strong List Hemispheric Differences
BOOK
text (.88)
page (.45)
library (.79)
story (.41)
chapter (.61)
title (.37)
novel (.60)
shelf (.36)
publisher (.53) encyclopedia (.26)
author (.49)
magazine (.24)
literature (.48) fiction (.20)
reader (.48)
BOOK
journal (.13)
volume (.04)
dictionary (.13) fairytale (.03)
study (.08)
history (.02)
address (.07)
telephone (.02)
words (.06)
caption (.01)
passage (.05)
grammar (.01)
editor (.05)
printing (.01)
series (.05)
Critical Words (36)
ARMY*
BABY
BAD
BIRD
BOAT
BOOK
BREAD*
CAR*
CHAIR*
CHURCH
COLD*
DEATH
DOCTOR*
FIRE
FISH
FLOWER
FOOD
FRUIT*
GOD
HORSE
KING*
LIE
MONEY
MUSIC*
NEEDLE*
ROCK
SAD
SCHOOL
SHIRT*
SICK
SLEEP*
SMART
SMELL*
SMOKE
SWEET*
TREE
* Words used by Roediger & McDermott (19995); McDermott (1995).
Results
100
High associative strength = text – BOOK
Lower associative strength = fairytale – BOOK
In the false-memory task, list strength can modulate the probability of falsely
remembering the critical word (Roediger et al., 2001). Applied to a
lateralized task, a strength manipulation could:
•Further define the contribution of each hemisphere in the formation of
memory for words.
•Specifically, show how list strength can modulate the asymmetry for the
false-memory effect.
Method
Study Phase
•Studied 36 lists before test.
•“Remember each word for a later test.”
•Math distractor between lists, 20 s – manual “yes/no” judgments.
Recognition Test
•Lateralized – brief exposure = 145 ms each
•Presented unstudied critical words, studied words, and unrelated words
to the LH & RH
•Subjects responded “yes, I studied the word,” or “no, I didn’t study the
word.”
rvf-LH
lvf-RH
90
Percent Correct (%)
The strength of the relationship between words on the traditional falsememory lists is mixed. Not all are indexed as high strength through norming
(Nelson et al., 1998).
Weak List Hemispheric Differences
•Critical words, RH > LH in false recognition, but no significant
difference
•Studied words, RH > LH in correct recognition, but no significant
difference
Conclusions
Strong and weak list conditions result in differential hemispheric performance
…
•Found associate strength modulates the false-memory effect across
visual fields.
•Showed a pattern of higher meaning accessibility in both hemispheres
based on list strength.
•Accuracy for the studied words and false memory for the critical
words went hand in hand.
•Provides a further explanation of the false memory asymmetry
observed in previous divided-visual field research.
Future Directions
Probability of Recognizing a Word During Test
Effect of High Association Strength
•Critical words, LH > RH in false recognition
•Studied words, LH > RH in correct recognition
• In an attempt to provide a robust list strength manipulation, the weak lists may
have been to weak to produce the false-memory effect. New, slightly stronger
weak lists may produce the effect.
• Investigate other variables that may better predict the differences in hemispheric
processing of false memories, such as category lists and feature overlap.
80
References
70
60
50
40
30
20
Strong Weak
Strong Weak
Critical
Studied
Strong Weak
Unrelated
Beeman, M. (1998). Coarse semantic coding and discourse comprehension. In M. Beeman & C. Chiarello (Eds.),
Right hemisphere language comprehension (pp. 255-284). Mahwah, NJ: Lawrence Erlbaum associates.
Chiarello, C. (1998). On codes of meaning and the meaning of codes: Semantic access and retrieval within and
between hemispheres. In M. Beeman & C. Chiarello (Eds.), Right hemisphere language comprehension (pp. 141160). Mahwah, NJ: Lawrence Erlbaum Associates.
Ito, Y. (2001). Hemispheric asymmetry in the induction of false memories. Laterality, 6, 337-346.
Nelson, D. L., McEvoy, C. L., & Schreiber, T. A. (1998). The University of South Florida word association, rhyme,
and word fragment norms. http://www.usf.edu/FreeAssociation/.
Roediger, H. L., III, Watson, J. M., McDermott, K. B., & Gallo, D. A. (2001). Factors that determine false recall: A
multiple regression analysis. Psychonomic Bulletin & Review, 8, 385-407
Westerberg, C. E., & Marsolek, C. J. (in press). Hemispheric asymmetries in memory encoding as measured in a false
recognition paradigm. Cortex.