Introduction

Approximately 90% of the human population is right-handed [2]. Most of those individuals have left hemisphere dominance for handedness, as well as language [8]. This ‘typical’ pattern of asymmetrical lateralization is less pronounced and more often reversed in non-right-handers[3].

Hemispheric asymmetry is paradoxical and it is unclear how strong hand preference evolved, as studies of primate hand-use have yielded inconsistent findings [5]. Annett’s ‘Right Shift’ Theory is the most comprehensive hypothesis of how handedness is determined [1].

An increase in non-right-handedness has been observed in clinical schizophrenic populations and in healthy individuals with high scores on the Magical Ideation Scale (MIS) [4]. However, discordant findings are reported based on how hand preferences are measured and categorized [6].

With our growing acceptance that schizophrenia and potentially other disorders are related to a leftward shift in lateralization and weaker hand preferences, a standardized assessment for future studies will be a helpful tool for research into the genetic, developmental, and environmental foundations of lateralization and handedness.

Participants 176 students (135 female, 40 male, 1 unidentified) from St.

Mary’s College of Maryland, aged 17 – 41, participated in this study.

Materials Oldfield’s Edinburgh Handedness Inventory (EHI) consists

of 10 items, for which participants are asked to “indicate your preference in the use of hands in the following activities by putting ‘+’ in the appropriate [left or right] column. Where the preference is so strong that you would never try to use the other hand unless absolutely forced to, put ‘++.’ If in any case you are really indifferent put ‘+’ in both columns.” s on Scores range from -100 to 100, indicating strong left to strong right preference [7].

Annett’s Handedness Inventory assesses six identical tasks as the EHI: (1) writing; (2) throwing; (3) using scissors; (4) striking a match; (5) using a toothbrush; and (6) using a broom. It’s directions state “Please indicate which hand you habitually use for each of the following activities by writing ‘R’ (for right), ‘L’ (for left), or ‘E’ (for either).” Responses were scored on a scale from -12 to 12, from strong left to strong right preference [1].

Research Questions

1. Does the EHI or AHQ elicit a greater proportion of ‘Either hand’ responses?

2. Does the EHI or AHQ elicit a greater proportion of ‘Either hand’ responses on identical items?

3. Which assessment produces more ‘strong’ hand preference categorizations?

4. Which assessment accounts for more variation in MIS scores?

There were significantly more ‘strong’ hand preference classifications by the AHQ despite eliciting the same proportion of ‘Either Hand’ responses as the EHI, suggesting some initial evidence that the EHI is more effective at tapping into weak hand preferences.

Future comparisons of handedness inventories and measures of schizotypy should control demographic factors, such as gender and age, to improve generalizability.

Figure 4. A multiple linear regression was significant, F(2,173) = 3.44, p = .034. Only the EHI was a significant predictor of scores on the MIS, β = -.214, t(175) = 2.62, p = .01.

The Origin & Assessment of Hand Preferences: A Re-Evaluation of Clinical Implications

J.T. Bowers Mentor: Janet Kosarych-CoyDepartment of Psychology, St. Mary’s College of Maryland

Figure 2. The proportion of ‘Either Hand’ responses on identical items was not significantly different, t(175) = 1.37, p = .173.

Figure 1. The proportion of ‘Either Hand’ responses was not significantly different, t(175) = 1.92, p = .056.

Figure 3. There was a significantly higher proportion of ‘Strong’ hand preference categorizations made by the AHQ, t(175) = 2.49, p = .014.

[1] Annett, M. (1970). A classification of hand preference by association analysis. British Journal of Psychology, 61(3), 303-321.

[2] Annett, M. (1985). Left, right, hand and brain: The right-shift theory. Hove, U.K.: Erlbaum Ltd.

[3] Bourne, V. J. (2005). Lateralised processing of positive facial emotion: Sex differences in strength of hemispheric dominance. Neuropsychologia, 43, 953–956.

[4] Chapman, H. L., Grimshaw, G. M., & Nicholls, M. E. R. (2011). Going beyond students: An association between mixed-hand preference and schizotypy subscales in a general population. Psychiatry Research, 187(1-2), 89-93.

[5] Corballis, M. C. (2009). The evolution and genetics of cerebral asymmetry. Philosophical Transactions Of The Royal Society Of London. Series B, Biological Sciences, 364(1519), 867-879.

[6] Dragovic, M., & Hammond, G. (2005). Handedness in schizophrenia: A quantitative review of evidence. Acta Psychiatrica Scandinavica, 111(6), 410-419.

[7] Oldfield, R. C. (1971). The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia, 9(1), 97-113.

[8] Perelle, I. B., & Ehrman, L. (2005). On the other hand. Behavior Genetics, 35(3), 343-350.

[9] Winterstein, B. P., Silvia, P. J., Kwapil, T. R., Kaufman, J. C., Reiter-Palmon, R., & Wigert, B. (2011). Brief assessment of schizotypy: Developing short forms of the Wisconsin Schizotypy Scales. Personality and Individual Differences.

EHI AHQ0.12

0.16

0.2

Handedness Assessment

Prop

ortio

n of

Res

pons

es

EHI AHQ0.21

0.215

0.22

0.225

0.23

0.235

0.24

0.245

0.25

0.255

0.26

Handedness Assessment

Prop

ortio

n of

Res

pons

es

EHI AHQ0.56

0.58

0.6

0.62

0.64

0.66

0.68

0.7

0.72

0.74

Handedness Assessment

Prop

ortio

n of

Res

pons

es

Valid short-forms of the Magical Ideation Scale (MIS) and the Physical Anhedonia Scale (PAS) from the Wisconsin Schizotypy Scales were used [9]. The MIS consisted of 15 true/false items. For instance, “I have sometimes felt that strangers were reading my mind.” The PAS consisted of 15 true/false items. For instance, “The beauty of sunsets is greatly overrated.” Both inventories were scored from 0-15 [9].

Procedure Participants took one of two versions of a composite

survey containing the two handedness inventories and a mixture of the two schizotypy scales. Version A was ordered EHI-MIS/PAS-AHQ. Version B was ordered AHQ-MIS/PAS-EHI.

Raw totals on the EHI and AHQ were converted to absolute values; EHI scores were categorized as ‘right-handed’ if they were equal to or greater than 70 and ‘non-right-handed’ if they were below 70. Absolute scores on the AHQ were derived likewise using the cut-off point of 9. Both cut-offs were in accordance with the literature.

Results

Conclusions

Methods

References