Infants Use Compression Information to Infer Objects’ Weights: Examining Cognition, Exploration, and Prospective Action in a Preferential-Reaching Task


  • This research was supported by the Max-Planck-Institute for Human Cognitive and Brain Sciences, Munich, Germany, where the experiments were conducted; by Grants from CFI (203229) and NSERC (322013) to Petra Hauf; and by a Grant from NICHD (HD-021104) to Renée Baillargeon. We thank Kris Onishi for helpful suggestions; the Max-Planck-BabyLab Team, Kailee MacDonald, and Charlene Parker for their help with the data collection and coding; and the parents and infants who made this research possible.

concerning this article should be addressed to Petra Hauf, Department of Psychology, St. Francis Xavier University, PO Box 5000, Antigonish, NS, Canada B2G 2W5. Electronic mail may be sent to


The present research used a preferential-reaching task to examine whether 9- and 11-month-olds (n = 144) could infer the relative weights of two objects resting on a soft, compressible platform. Experiment 1 established that infants reached preferentially for the lighter of 2 boxes. In Experiments 2–4, infants saw 2 boxes identical except in weight resting on a cotton wool platform. Infants reached prospectively for the lighter box, but only when their initial exploratory activities provided critical information. At 11 months, infants succeeded as long as they first determined that the platform was compressible; at 9 months, infants succeeded only if they also explored the boxes and thus had advance knowledge that they differed in weight.