Mental object rotation and motor development in 8- and 10-month-old infants.

Recent evidence indicates that 6-month-old infants' mental rotation of objects profits from prior manual experience, whereas observational experience does not have the same beneficial effect. The current study investigated whether older infants, at 8 and 10 months, succeed in a mental rotation task after observational experience only and whether performance is related to infants' motor development. Using the violation-of-expectation paradigm, infants (N = 40) were presented with an asymmetrical object that was moved straight down behind an occluder. After the occluder was lowered, infants saw either the original object (possible event) or a mirror image of the original object (impossible event) in one of five different orientations (0° to 180° in steps of 45°). Results indicated that it was not until 10 months of age that infants looked longer at the impossible outcome. Analyses including parent questionnaire data showed that mental rotation performance was related to infants' motor development, emphasizing the importance of action experience for early cognitive development.