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Sex Differences in Visual Field Lateralization:
Where are they?
Christine
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Chiarello ,
Laura K.
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Halderman ,
Suzanne
University of California,
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Riverside ,
Introduction
Method
Janelle
University of Florida,
Multiple Regression:
• Hierarchical regressions were performed for each DVF task on Accuracy
and RT Asymmetry Scores with the predictors Sex, Handedness score,
Reading Subtests, VIQ, PIQ, and the asymmetry scores for the other tasks.
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Females
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• Accuracy: when Sex was entered as the first predictor, it accounted for
significant variance in only two tasks - Category Generation (19.6%) and
Nonword Naming (2%), p < .05. Of this variance only 2.7% was unique to
Sex, and only for Category Generation, p < .01.
• RT: when Sex was entered as the first predictor, it accounted for no
significant variance for any of the tasks. Sex accounted for unique variance
only for Semantic Decision (2.7%), p < .05.
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Cross-Task Asymmetry Correlations:
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Le xical
De cis ion
Mas k e d Word
Re cognition
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Wor d
Nam ing2
Nonw or d
Nam ing
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Ge ne r ation
Cate gor y
Ge ne r ation
• Accuracy: out of 34 possible task correlations, males demonstrated
stronger cross-task correlations for 12 task comparisons, and females
demonstrated stronger cross-task correlations for 12 other task comparisons.
• RT: out of 34 possible task correlations, males demonstrated stronger
cross-task correlations for 10 task comparisons, and females demonstrated
stronger cross-task correlations for 9 task comparisons.
Task
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Females
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• There is no evidence for sex differences in the strength of cross-task
asymmetry correlations.
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Conclusions
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Le xical
De cis ion
Mas k e d Word
Re cognition
Wor d
Nam ing1
Wor d
Nam ing2
Nonw or d
Nam ing
Se m antic
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Ge ne r ation
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Task
PARTICIPANTS:
• 100 male, 100 female native English speakers
• 18-34 years of age
• 28 (14%) are not right-handed
Christiana M.
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Leonard
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Gainesville
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Accuracy Asymmetry
The current study, part of the Biological Substrates for
Language Project, affords the opportunity to explore this issue in
another large-scale investigation. In this project 200 individuals
were tested in eight divided visual field tasks exploring different
aspects of lexical processing. This multi-task approach enables a
powerful test of the hypothesis that women have more bilateral
language lateralization. This position would be supported if women
show reduced asymmetries for all or most of the tasks. We
employed three analytic approaches to address this issue. First, we
used analysis of variance to investigate the reliability of sex X visual
field interactions across our tasks. Second, multiple regression was
used to examine whether sex was a significant predictor of
asymmetry in each of our tasks. Finally, we computed the cross-task
asymmetry correlations separately for males and females, in order to
determine whether lexical asymmetries would be more strongly
intercorrelated for males than females.
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Results
RT Asymmetry
It is frequently claimed that women have a more bilateral
organization for language as compared to men. However,
experimental support for this claim has been mixed. Although sex
differences are sometimes obtained in divided visual field
experiments, they rarely replicate, and a recent large-scale study
found little evidence for sex differences in functional lateralization
(Boles, 2005). In that study, across six laterality tasks (both verbal
and nonverbal material) sex accounted for less than 1% of the
variance in lateral asymmetry.
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Accuracy (above) and RT (below) Asymmetry Scores for males and
females by task.
This large-scale investigation provided little evidence for sex differences
in the lateralization of language processing. Across a range of lexical tasks
with varying degrees of asymmetry, no across-the-board sex differences were
observed. If there are sex differences in language lateralization, these are
highly task- and measure-specific, and account for little systematic variance.
These results do not support the view that women have a more bilateral
organization for language, and confirm Boles’ (1995) earlier findings with
different tasks. Occasional reports in the literature of sex X VF interactions
may be due to inadequate sample sizes that are unrepresentative of the
wider population.
Positive scores indicate a RVF/LH advantage.
DVF TASKS:
• Lexical Decision
• Masked Word Recognition (2 AFC procedure)
• Word Naming (administered twice with different stimuli)
• Nonword Naming
• Semantic (manmade vs natural) Decision
• Verb Generation
• Category Generation
PROCEDURE:
• DVF tasks administered across 4 sessions
• RT and Accuracy (% correct) recorded
Analysis of Variance:
• Accuracy: there was no Sex X Visual Field interaction, but the Sex X Task
X Visual Field Interaction was reliable, F(7,1385) = 3.05, p<.01. Separate
analyses by Task indicated that males had stronger asymmetries for Nonword
Naming, F(1,198)=4.68, p<.05 and Category Generation, F(1,198)=4.28, p
<.05.
• RT: there was no Sex X Visual Field interaction, nor was Sex X Task X
Visual Field reliable (Fs < 1). Separate analyses by Task indicated no Sex X
Visual Field interactions for any task.
References
Boles, D.B. (2005). A large-sample study of sex differences in functional
cerebral lateralization. Journal of Clinical and Experimental
Neuropsychology, 27, 759-768.
Acknowledgment
This research was supported by NIDCD grant 5R01DC6957.