Handedness and schizotypy in non-clinical populations: Influence of handedness measures and age on the relationship

This study aimed to evaluate the relation of handedness to schizotypal personality, with the influence of different handedness measures and age on the relationship investigated as well among representative samples of school students and community adults in Taiwan, where social pressure against certain left-handed actions was strong. In a total of 175 primary school students, 1020 junior high-school students, and 342 adult participants aged 20 to 65 years, all the participants completed the 12-item Annett handedness questionnaire, and the latter two groups further completed the Schizotypal Personality Questionnaire (SPQ) and the Perceptual Aberration Scale (PAS). There was a trend of increasing non-right handedness with younger age groups. Two classification methods in handedness, Annett's or Briggs-Nebes' three-category classification, led to very different frequency distribution and relation to schizotypy. For the adolescents, either Annett's classification or quantitative measures (Hand Preference Index and either-hand use scores) in handedness exhibited an association with schizotypy, whereas for the adults the either-hand use score was the only measure that did so. In contrast, no such difference was found using the Briggs-Nebes' classification method. The association of the non-right or mixed handedness was more consistent and of greater magnitude with the positive aspect of schizotypy, especially the PAS and the Cognitive-perceptual Dysfunction of the SPQ. The results highlight the potential of adolescents for future investigation on certain common causes underlying atypical cerebral lateralisation and positive schizotypy.