relationships between performance and hemispheric asymmetry on lexical tasks suzanne e. welcome 1,...
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Relationships between performance and hemispheric asymmetry on lexical tasksSuzanne E. Welcome1, Christine Chiarello1, Laura Halderman2, & Christiana Leonard3
1University of California, Riverside2University of Pittsburgh
3University of Florida, Gainesville
Participants200 university students (100 female, 100 male; 14% non-right handed)Psychometric Measures•Verbal and Performance IQ (Wechsler, 1999)•Word Identification, Word Attack, and Passage Comprehension (Woodcock, 1998)Divided Visual Field Tasks•Word Naming•Nonword Naming•Masked Word Recognition•Lexical Decision•Semantic Decision•Category Member Generation•Verb Generation•Average Z-scored asymmetry for each task used as Composite Asymmetry Score Asymmetry Indices: Correlations between asymmetry index and percentile ranks on psychometric measures calculatedMultiple RegressionPredict performance on psychometric measures from DVF difference score with average DVF performance partialled out
Signed indices and their absolute values were tested separately
Methods
Results
Conclusions
• Do individuals who show stronger lateralization of word recognition processes perform better on reading and IQ measures?
-Previous study showed positive correlations between asymmetry and performance on dichotic listening tasks (Boles, Barth, & Merrill, 2008). We investigated whether this relationship extends to performance on standardized measures of verbal ability. - Do different types of word recognition tasks show different degrees of relationship?
• Do different statistical approaches to evaluating asymmetry identify same relationships between asymmetry and psychometric performance?
-Are measures of direction of asymmetry (signed) or degree of asymmetry (absolute value) more predictive?-Asymmetry index calculates ratio of difference to average RT or accuracy
-Focus is on relationship between asymmetry and average RT or accuracy
-Multiple regression with average RT or accuracy partialled out
- Focus is on variance accounted for by difference score once variance due to average RT or accuracy has been removed
Introduction
References
This research was supported by NIH grant DC006957.
•Within the normal population, individuals who show greater lateralization in word recognition processes perform better on standardized measures of verbal ability.
-Degree of asymmetry relates slightly more strongly to psychometric performance than directional measure.
•For accuracy, multiple regression reveals relationships between asymmetry and psychometric performance relationships that correlations with asymmetry indices do not
-Average task accuracy shows positive relationship with psychometric performance independent of task asymmetry-This relationship is treated differently in different statistical approaches - variance due to average task accuracy is controlled for in multiple regression approach but contributes to asymmetry index
Relationship between visual field difference and average accuracy (asymmetry index) is not predictive of reading or IQ scoresIf variance due to average task accuracy is accounted for, visual field difference is predictive of reading and IQ scores
•Tasks showing strongest relationship with performance on standardized tests of verbal ability are word recognition tasks, especially masked word recognition RT and lexical decision accuracy.
- Stronger lateralization of single word recognition processes may confer an advantage for reading and verbal IQ.
Boles, D.B., Bart, J.M. & Merrill, E.C. (2008). Asymmetry and performance: toward a neurodevelopmental theory. Brain and Cognition, 66(2), 124-139.
Wechsler, D. (1999). Wechsler Abbreviated Scale of Intelligence. San Antonio, TX: The Psychological Corporation.
Woodcock, R.W. (1998). Woodcock Reading Mastery Test-Revised Normative Update (WRMT-R). Circle Pines, MN: American Guidance Service, Inc.
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Verbal
IQ
Performance
IQ
Word
Identification
Word
Attack
Passage
Comp.
Correlation NS NS NS .034* .034*
Mult. Regress. .020* NS NS .034* .031*
For both correlational analyses and multiple regression (presented below), absolute values of asymmetry account for a slightly higher percentage of variance in verbal performance than signed measures.
Verbal
IQ
Performance
IQ
Word
Identification
Word
Attack
Passage
Comp.
Correlation NS NS NS NS NS
Mult. Regress. .049* NS .027* .035* .040*
For RT, composite asymmetry accounts for similar amounts of variance in psychometric test performance when using multiple regression approach (semi-partial r2) and correlations with asymmetry indices (squared correlation coefficients).
Composite Asymmetry
Measure
Verbal
IQ
Performance
IQ
Word
Identification
Word
Attack
Passage
Comprehension
Signed Acc. .038 NS .047 .034 .032
Abs. Val. Acc. .049 NS .027 .035 .040
Signed RT NS NS NS NS .032
Abs. Val. RT .020 NS NS .034 .031
For accuracy, multiple regression approach reveals asymmetry/performance relationships that correlations with asymmetry indices do not
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120
-1.5 -1 -0.5 0 0.5 1 1.5 2
Residualized Accuracy Asymmetry (Absolute Value)
Passage Comprehension (Percentile)
Where relationships between lateralization of word recognition and performance on standardized measures of verbal ability exist, individuals who show greater asymmetry perform better.
Verbal IQ
Word ID
Word Attack
Passage Comp.
Nonword Naming RT
Masked Word Recog. Acc
Word Naming Acc
Nonword Naming Acc
Masked Word Recog. RT
Lexical Decision Acc
Tas
k A
sym
met
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Per
form
ance
Mea
sure
Asymmetry of some individual word recognition tasks predicts performance on standardized measures.