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

0

20

40

60

80

100

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

ry

Per

form

ance

Mea

sure

Asymmetry of some individual word recognition tasks predicts performance on standardized measures.