Research on the early development of auditory localization responses is reviewed and the existence of a U-shaped developmental function is described. It has been reported that many newborns turn towards off-centred sound sources reliably at birth and will perform well for approximately the first month of life, poorly during the second and third months, and well again during the fourth month. This trend was confirmed in three of four infants who were tested extensively throughout their early months. The fourth baby failed to show reliable orientation towards sounds until the fourth month of life. During the period of temporary performance decrement, attempts to reinstate reliable responding by either introducing meaningful acoustic stimuli or eliminating possible auditory-visual conflicts were not successful. Potential explanations for this temporary decline in auditory orientation responses are discussed.*We wish to thank A. Muir, J. Rodger, and P.C. Dodwell for their helpful criticisms of this paper; M.K. Buell, H. Killen, B. Pater, and M. Sinclair who helped us test some of the babies; L. Paterson who helped score tapes; Rachel Clifton who helped us acquire a low-light-level videocamera; and A. Lister who typed the manuscript. We would also like to thank the mothers and their infants (J-H.

This research reports a first attempt to study adaptation to laterally displacing prisms in human infants of ages six to ten months. Twenty infants were tested over four days under conditions similar to those used in adult adaptation studies. Evidence was found of vigorous adaptation when infants were exposed to base-right prisms under conditions of active exposure. Detailed consideration is given to the conditions and methods of studying adaptation in infants and implications for adult studies.

This study replicated a previous demonstration of prism-induced aftereffects in 5-9-month-old infants. Aftereffects were considered to be changes in direction of reaching for visual targets following prism exposure. The present study employed a longitudinal design. In the experimental group, infants were exposed to 25-diopter lateral displacing prisms once each month from 5 to 9 months. Since many of the subjects were unable to complete testing at 5 months, data for that age level were not included in the main analyses. In a control group, infants were tested each month but were exposed to prisms only at 9 months of age. The magnitude of aftereffects for control subjects at 9 months was not significantly greater than aftereffects obtained for experimentals at 6 months, so there was little evidence of changes in adaptability due to age or repeated exposure to the prisms. The finding of an increase in the frequency of reaching with the left hand during exposure to leftward-deviating prisms was replicated. Such a shift in hand preference probably represents an alternative form of adaptation which for methodological reasons has not been observed in adults. The aftereffect and frequency results were complementary and provide a clear demonstration of adaptation to prismatic displacement between 6 and 9 months.

This study replicated a previous demonstration of prism-induced aftereffects in 5-9-month-old infants. Aftereffects were considered to be changes in direction of reaching for visual targets following prism exposure. The present study employed a longitudinal design. In the experimental group, infants were exposed to 25-diopter lateral displacing prisms once each month from 5 to 9 months. Since many of the subjects were unable to complete testing at 5 months, data for that age level were not included in the main analyses. In a control group, infants were tested each month but were exposed to prisms only at 9 months of age. The magnitude of aftereffects for control subjects at 9 months was not significantly greater than aftereffects obtained for experimentals at 6 months, so there was little evidence of changes in adaptability due to age or repeated exposure to the prisms. The finding of an increase in the frequency of reaching with the left hand during exposure to leftward-deviating prisms was replicated. Such a shift in hand preference probably represents an alternative form of adaptation which for methodological reasons has not been observed in adults. The aftereffect and frequency results were complementary and provide a clear demonstration of adaptation to prismatic displacement between 6 and 9 months.

No abstract