Haptic memory and handedness in 2-month-old infants.

This study examined the robustness of infant haptic memory, asymmetry between hands, and sex differences in haptic memory in infancy. A total of 96 2-month-old infants (half males, half females) were habituated haptically to an object with their right and their left hand, out of the field of view. Haptic memory was then tested under three conditions: after haptic interference, after a 30-second delay, or after no delay. The results show that haptic habituation occurred for both hands. The girls needed more time to habituate with their left hand than with their right hand, and they habituated more slowly than the boys did. Discrimination was also found in both hands and in both sexes. Haptic delayed recognition memory was only found in young boys mainly after a short delay and under certain conditions after interference. In young girls, recognition memory was found after interference only with the left hand. This result seemed to depend on the information processing speed. Thus, for memory performance, a sex difference was clearly observed. Moreover, the infants' left hand retained better information on object shape than did the right hand for both the sexes. Asymmetries in infancy are discussed in connection with the difference in brain maturation rate.