A Computational Developmental Model of the Implicit False Belief Task

A Computational Developmental Model of the Implicit False Belief Task Vincent G. Berthiaume (Vincent.Berthiaume@McGill.ca) Department of Psychology, 1205 Dr. Penfield Avenue Montreal, Qc, H3A 1B1 Canada Kristine H. Onishi (Kris.Onishi@McGill.ca) Department of Psychology, 1205 Dr. Penfield Avenue Montreal, Qc, H3A 1B1 Canada Thomas R. Shultz (Thomas.Shultz@McGill.ca) Department of Psychology and School of Computer Science, 1205 Dr. Penfield Avenue Montreal, Qc, H3A 1B1 Canada years and eight months (Wellman, Cross, & Watson, 2001) will typically say that Sally will search in the box, an expectation that is consistent with an omniscient ToM – i.e., Sally will search in the actual location of the object. An older child will instead typically say that Sally will search in the basket, an expectation that is consistent with a representational ToM – i.e., Sally will search for the object in accord with her mental representation of its location. Recently, 15-month-olds were shown to solve a visual, implicit version of the task (Onishi & Baillargeon, 2005). Because it avoids the complexities of language, the implicit task is more amenable to computational modeling. This paper introduces a connectionist model that learns to solve the implicit false-belief task and that reproduces the omniscient-to-representational ToM transition when training contained more true- than false-belief trials. Abstract Do children understand that others have mental representations, for instance, mental representations of an object’s location? This understanding, known as a representational Theory of Mind (ToM) has typically been studied using false-belief (FB) tasks. Standard, verbal FB tasks test whether a child can use protagonists’ beliefs to say that they will search for objects where they last saw them. Whereas children under 3.5 years typically fail the task and expect protagonists to search where objects are (expectation consistent with an omniscient ToM), older children expect protagonists to search where they last saw the objects (expectation consistent with a representational ToM). Recently, 15-month-olds were shown to succeed at a visual, implicit version of the task. We present a sibling-descendant cascade-correlation connectionist model that learns to succeed at an implicit FB task. When trained on twice as many true- as false-belief trials, our model reproduced the omniscient-to- representational transition observed in explicit tasks. That is, networks first had expectations consistent with an omniscient ToM, and after further training had expectations consistent with a representational ToM. Thus, our model predicts that infants may also go through a transition on the implicit task, and suggests that this transition may be due in part to people holding more true than false beliefs. The Implicit False-Belief Task Onishi and Baillargeon (2005) used a violation-of- expectation paradigm to show that 15-month-olds could pass an implicit, language-free version of the false-belief task. This paradigm uses looking time as a dependent measure of surprise. Infants – just like adults – look longer at the unexpected. Infants were seated on their parent’s lap and watched an actor performing actions with two boxes (one green and one yellow) and an object (Onishi & Baillargeon, 2005). First in familiarization trials, infants were shown the actor puting the object in the green box, as if to hide it there. Then on two trials the actor searched in the green box as if to retrieve the object (without actually revealing it) to convey to infants that she wanted it. Next, infants saw one of four belief- induction trials designed to cause the actor to hold either a true belief (TB) or a false belief (FB) that the object was either in the green or yellow box. For instance, in the TB- yellow trial, infants saw the actor watching as the object moved from the green box to the yellow box, thus causing the actor to hold a TB that the object was in the yellow box. By contrast, in the FB-green trial, another group of infants saw, as the actor was absent from the scene, the object move from the green into the yellow box, thus causing the actor to Keywords: False beliefs; theory of mind; connectionism. Background Do children understand that others have mental representations, for instance, mental representations of an object’s location? This understanding – known as a representational Theory of Mind (ToM, Wimmer & Perner, 1983) – has been found, using explicit false belief tasks, to go through a developmental transition between 3 and 4 years of age. In this task, children see a puppet named Sally put a marble in a basket that is next to a box. While Sally is gone, another puppet, Anne, moves the marble from the basket to the box, thereby leaving Sally with the false belief that the marble is still in the basket. To predict that Sally will search for the marble in the basket, children must understand that she has a mental representation of the scene that is not consistent with reality (Dennett, 1978). A child under three