Genes Take Over When the Input Fails: A Twin Study of the Passive

1. Genes Take Over When the Input Fails: A Twin Study of the Passive Jennifer B. Ganger1, Sabrina Dunn1, Peter Gordon2 1University of Pittsburgh, 2Columbia University Participants Results Heritability (h2) and shared environment (c2) by actionality MZ and DZ correlations by actionality Replication of actionality effect t = 17.321; P < .0001 • Genes and Environment in Syntactic Development • Are individual differences in the timing of syntactic development determined by environmental or genetic factors? • Do these two influences differ depending on the availability of appropriate linguistic input? • Heritability and Twin Studies • Twin studies can address these questions by comparing the effects of heritability and shared environment for performance on linguistic tasks • The Twin Method • Subjects: 69 Identical (MZ) and 117 fraternal (DZ) twins reared together • Correlations between twins: • r(MZ) = 100% shared genes + shared environment • r(DZ) = 50% shared genes + shared environment • Heritability (h2): Twice the difference between MZ and DZ correlations • = Influence of genetic factors:r(MZ) - r(DZ) x 2 • Shared environment (c2): MZ correlation minus heritability • = Influence of shared experience, such as linguistic input: r(MZ) - h2 • Summary of Results • Actional Passives • Show no heritability and strong effects of shared environment • Non-actional Passives • Show high heritability and no effect of shared environment Example Procedure(from Gordon & Chafetz, 1990) “John’s favorite movie is the Wizard of Oz. It was on TV, so he stayed inside to watch it.” Was the TV watched by John? Was John watched by the TV? (Children trained in advance to answer each pair of questions with one “yes” and one “no.”) • Acquisition of Passives • Passives are acquired gradually during the pre-school years and beyond • Actional passives (kicked, eaten) are mastered before non-actional passives (seen, liked) • 3 Theoretical Interpretations of Actionality Effect • Pinker, LeBeaux, & Frost (1987). Affectedness constraints on passivization.Child initially restrict passives to action verbs, then admits narrow classes of non-action verbs as passivizable • Gordon & Chafetz (1990) Predominance of actional passives in linguistic input. Verbal passives in children’s language input are almost exclusively actional. Non-action verbs occur only as adjectival (stative) passives. Non-actional passives are slower to be acquired because acquisition occurs on a verb-by-verb basis in the early stages with only limited generalization • Borer & Wexler (1987). Maturation of A-chains / Universal Phase Hypothesis. Action passives are interpreted as adjectival lacking A-chains. Non-action passives cannot be interpreted as adjectival and therefore reveal lack of A-chains that are subject to maturational constraints • Interpretation of Results • Not predicted by affectedness account • Consistent with FREQUENCY explanation • Actional passives frequent in linguistic input: External environment predicts rate of acquisition • Non-actional passives rare in linguistic input: Requires internal/cognitive processes which show influence of genetic differences • Consistent with A-chain maturation • Actionals acquired initially as adjectival passives • Non-actionals acquired as verbal passives lacking A-chains. Maturation of A-chains predicts genetic influences on rate of acquisition • 9 actional full passives: • dropped, eaten, carried, kissed, held, washed, shaken, hugged, kicked • 9 non-actional full passives: • Watched, forgotten, heard, known, remembered, believed, liked, seen, hated Participants References Gordon, P. & Chafetz, J. (1990). Verb-based versus class-based accounts of actionality effects in children’s comprehension of passives. Cognition, 36, 227-254. Borer, H., & Wexler, K. ) (1987). The maturation of syntax. In Roeper & Williams (eds), Parameter Settting, 23-172. Dordrecht: Reidel. Maratsos, M., Fox, D.E.C., Becker, J.A., Chalkley, M.A. (1983). Semantic restrictions on children’s early passive. Cognition, 19, 167-191. Pinker, S., LeBeaux, D.S., & Frost, L.A. (1987). Productivity and constraints in the acquisition of the passive. Cognition, 26, 195-267.