Investigating how infants learn to search in the A-not-B task

Investigating how infants learn to search in the A-not-B task Hanna Popick, 1 Melody Dye, 1 Natasha Kirkham 2 & Michael Ramscar 1 Department of Psychology, Stanford University Department of Psychological Sciences Birkbeck College, University of London Abstract Piaget (1954) first described what are often called “A- not-B errors” in infants: 8- to 12-month infants will generally search successfully for an object in one location (A), but then fail to search for it when it is conspicuously hidden in a new location (B). Subsequent studies have confirmed that in actively searching for hidden objects, infants robustly make prototypical A-not-B errors, ignoring the most recent location of objects when they search for them after a switch (Marcovitch & Zelazo, 1999; Wellman, Cross, Bartsch, & Harris, 1986). In seeking to explain this, accounts often focus on the possibility that infants’ errors stem from problems associated with implementing a correct search, such as limited working memory and inhibitory control, or from weak memory traces for the object and hiding location (e.g. Baillargeon, Graber, Devos, & Black, 1990; Diamond, 1988; Diamond, Cruttenden, & Neiderman, 1994; Munakata, 1997; Thelen, Schoner, Scheier, & Smith, In what follows, we explore an alternative, though complementary approach. Rather than assuming that a child already understands how to search, we consider what might be expected if a child were learning how to search. As noted above, in learning how to successfully seek out objects, children have to figure out that some things may be more likely to be where they were last seen, and others where they are most often seen, and they have to learn which strategy is most appropriate in each context. How might children learn search strategies, and their appropriate application? One way to consider these questions is within the framework provided by formal learning theories (e.g. Rescorla & Wagner, 1972), which see learning as the process of acquiring information about the relationship between events (outcomes) in the environment, and the cues that allow them to be predicted. From this perspective, children learn to search via a process of trial and error, strengthening or weakening the value of cues depending on their predictive successes and failures. This takes time. Infants must make, and learn from, more or less successful predictions before they can “master” search, and begin to match search strategies to context. As we shall show, while to an adult, children’s search behavior may appear to be erroneous (“perseverative”) from this perspective, a child’s A-not-B “errors” can be seen as a rational, inevitable part of the process of learning to search. In searching for hidden objects, infants younger than 12 months frequently commit the classic “A-not-B error,” in which they successfully search for an object in one location (A) and then fail to search for it when it is conspicuously hidden in a new location (B). The question is why they fail to make the switch and perseverate at the first location. While these errors have often been attributed to cognitive limitations or stages of neurological development, we propose that they are consistent with the early stages of learning. We present a context-learning model of “A-not-B” search, in which learning to adopt the appropriate search strategy involves attending to appropriate contextual cues. We then present the findings of an eye-tracking experiment with 9 month-olds that behaviorally supports the predictions of our learning model. Keywords: A-not-B, Learning Modeling, Causal Reasoning Theory, Computational Introduction It’s Monday morning. You haven’t seen your car keys since Friday. How do you find them? In an ideal world, you might just go look where you last saw them. You’ve learned, after all, that keys don’t usually move on their own, and that what best predicts a key’s location is the conjunction of a given spot and you having last seen the key at that spot. (So you might even attempt this search pattern if that “last spot” is a very strange place for keys to be.) But what if the world is less than ideal—what if you’re not sure where you last saw the keys? You may have other memories of them—clear recollections of them hanging on the hook reserved especially for your car keys, for example—which might compete with your memories from Friday. Indeed, if you aren’t sure where you last saw them, you may still check the hook first, because you know that searching at a location where the keys are seen frequently can be a successful search strategy. This characterization of adult “expertise” when it comes to looking for keys sheds light on the task facing a child learning how to find things in the world. A child must learn that things are likely to be at the location they were last seen, that things are also likely to be at the location they are most often seen, and that a successful search will involve weighing these considerations against what the child can remember about the last and most likely locations of an object. From this perspective, “perseverative errors,” in which a child searches for an object in a likely location rather than in the hiding location they just witnessed might be seen as a misapplication of what in other circumstances might be a completely rational strategy. The A-not-B Task In the classic A-not-B task (Piaget, 1954), 7 to 12-month- old children search for a small object in one of two identical hiding spots. The object is first hidden in plain view of the