TWIN STUDY OF VERBAL AND SPATIAL ABILITIES

Verbal and spatial abilities are recognized as highly heritable specif ic cognitive abilities. The purpose of this study was to perform the f irst behavioral genetic analysis of these abilities in a Croatian samp le. A total of 160 same-sex twin pairs took part in the investigation. Their ages ranged from 15 to 19 years. Pairs with doubtful zygosity w ere excluded from the analysis, so the final analysis was carried out on 71 monozygotic (35 male and 36 female) and 78 dizygotic (43 male an d 35 female) twin pairs. The twins were tested in small groups with fo ur tests designed to measure two factors of verbal abilities (vocabula ry and word fluency) and two factors of spatial abilities (spatial vis ualization and spatial orientation). For each of the tests substantial heritable variation was found. Respectively, intraclass correlations for monozygotic and dizygotic twins were 0.75 and 0.44 for visualizati on, 0.58 and 0.33 for spatial orientation, 0.67 and 0.41 for word flue ncy, and 0.74 and 0.41 for vocabulary. In addition, data were compared with several univariate LISREL models. Univariate model fitting resul ted in heritability estimates of 63, 49, 52 and 61% for visualization, spatial orientation, word fluency and vocabulary, respectively.