Children's comprehension and production of transitive sentences is sensitive to the causal structure of events

Children’s comprehension and production of transitive sentences is sensitive to the causal structure of events Melissa E. Kline 1 , Jesse Snedeker 2 , & Laura E. Schulz 3 (mekline@mit.edu, snedeker@wjh.harvard.edu, lschulz@mit.edu) Department of Brain and Cognitive Sciences 1,3 Massachusetts Institute of Technology 43 Vassar Street, Cambridge, MA 02139 Department of Psychology 2 Harvard University 33 Kirkland Street,Cambridge, MA 02138 Abstract such sentences are likely to describe events which have prop- erties of physical causation: motion, contact, exertion of force, and causation (Kako, 1998). Young children learn about causal structure not only from ob- servation, but also from the language they hear. Two novel- verb studies show that preschoolers expect transitive sentences like ‘Sarah broke the lamp’ to express relationships between cause and effect. Previous work has conflated causation with other semantic features, presenting children with coarse con- trasts between scenes varying on multiple dimensions. The current studies used minimal-pair scenes that varied on a sin- gle causally-relevant feature, the spatiotemporal contiguity be- tween action and outcome. Preschoolers were more likely to produce transitive descriptions (She wugged it) to describe causal versions of events. They also reliably selected causal versions when asked to find where she wugged [it]. Transitive syntax thus provides children with a rich source of evidence about the verbs they learn and the events they encounter in the world. Keywords: Language acquisition; Causality; Argument structure Introduction Information about causal relationships is embedded in the structure of the language that young children hear every day. In addition to explicitly causal constructions like ‘The ham- mer made the lamp break’, children hear many transitive sen- tences like ‘Sarah broke the lamp.’ Although these sentences are argued to express causation in adult grammars (in con- trast to intransitive sentences like ‘The lamp broke’, Levin & Rappaport-Hovav 2005), causal transitive sentences are syn- tactically identical to noncausal transitives like ‘Sarah sees the lamp’ and ‘Sarah resembles her sister.’ Thus, transitive syntax does not provide a deterministic cue to causal struc- ture. Despite this variation, there are several reasons to believe that adults and children have a bias to interpret transitive sen- tences causally. First, across languages, verbs of direct ex- ternal causation are consistently expressed with transitives, whereas the encoding of noncausal verbs is more variable. For instance, in Russian sentences like ‘The supervisor man- ages the department’ must be expressed in a non-transitive sentence (‘The supervisor manages over the department’; Levin & Rappaport-Hovav, 2005). Second, when adults are asked to guess the meaning of ‘jabberwocky’ transitive sen- tences like ‘The glob blebbed the meemor,’ they report that Critically, young children also show signs of this bias: they make and accept transitive overregularizations (‘The rab- bit disappeared’ → *‘The magician disappeared the rabbit’) more readily with verbs that describe a (caused) change of state or motion (Ambridge, Pine, Rowland & Young, 2008; Pinker, 1989). Even children as young as 28 months prefer to associate a new transitive sentence with an event involving causation (e.g., break) rather than one that simply involves contact (e.g., touch; Naigles, 1996). This suggests that there may be early links between causal semantics and transitive syntax. In the present studies, we explore whether 3- and 4-year- old children’s expectations about novel transitive sentences are specifically sensitive to causality. To do this, we control other event features and vary only a single dimension that is relevant to causal relationships, namely the presence or ab- sence of a spatiotemporal gap between an agent’s action and a physical outcome. In nonlinguistic tasks, we know that even young infants are sensitive to spatiotemporal cues in distin- guishing causal and noncausal events (Leslie & Keeble, 1987; Muentener & Carey, 2010). These abilities allow children to learn about the world and design effective interventions on causal processes. However, although children learn a great deal about the world around them through the testimony of others (Harris & Koenig, 2006), relatively little is known about how chil- dren map causal relationships into language. This is surpris- ing, given that testimony about causal properties can make a significant difference to children’s understanding of causal events. Children shift from perceptually-based to causally- based categorization if causal language is used to describe objects (Nazzi & Gopnik, 2000; Nazzi & Gopnik, 2001), preschoolers explore perceptually identical objects with dis- parate causal properties more if the objects share a common label (Schulz, Standing, & Bonawitz, 2008), and 2-year olds who have learned that event A predicts event B only inter- vene on A to try to cause B if the events are described with