Hemispheric Asymmetries In False Recognition May Depend on Associative Strength

Cathy S. Robinson & Christine ChiarelloUniversity of California, RiversideIntroduction

Semantic EncodingThe 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.

Effect of High Association StrengthThe strength of the relationship between words on the traditional false-memory lists is mixed. Not all are indexed as high strength through norming (Nelson et al., 1998).

High associative strength = text – BOOKLower 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.

False Memory & Divided Visual Field StudiesWesterberg & 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.

DesignLateralized false-memory task with three conditions: list backwards association strength (strong, weak), visual field (rvf-LH, lvf-RH), and word type (critical, studied, unrelated).

PredictionsIn 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.

Experiment Design & Predictions

MethodStudy 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.”

Weak List (M = .051)

BOOKjournal (.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)

Strong List (M = .447)

BOOKtext (.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)

Critical Words (36)

ARMY* CHURCH GOD SCHOOLBABY COLD* HORSE SHIRT*BAD DEATH KING* SICKBIRD DOCTOR* LIE SLEEP*BOAT FIRE MONEY SMARTBOOK FISH MUSIC* SMELL*BREAD* FLOWER NEEDLE* SMOKECAR* FOOD ROCK SWEET*CHAIR* FRUIT* SAD TREE

* Words used by Roediger & McDermott (19995); McDermott (1995).

ResultsProbability of Recognizing a Word During Test

20

30

40

50

60

70

80

90

100

Strong Weak Strong Weak Strong Weak

Critical Studied Unrelated

Per

cen

t C

orr

ect

(%)

rvf-LHlvf-RH

Strong List Hemispheric Differences

•Critical words, LH > RH in false recognition•Studied words, LH > RH in correct recognition

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

ConclusionsStrong 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

ReferencesBeeman, 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. 141-160). 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.

•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.