Effective action by infants to contact objects by reaching and leaning.

The ability of infants aged 8-12 months to coordinate their arm and trunk movements to contact an object located in different positions was investigated in 2 experiments. In the first, 8- and 10-month-old infants reached for near objects but both reached and leaned for more distant ones indicating that they perceived that forward leaning extends the range of contact beyond that of reaching alone. In addition, arm and trunk movements were initiated simultaneously; visual information concerning object distance was sufficient to activate an integrated reaching-and-leaning response. Object distances were increased and a mechanical aid was provided on half the trials in the second experiment with 10- and 12-month-old infants. For both age groups the degree of leaning was reduced for objects that were out of reach without the aid. Only older infants were able to use the aid to extend partially their range of contact. Overall the results support the conclusions that, by at least 8 months, infants perceive that leaning extends their effective reaching space; by 10 months they perceive the limits within which reaching together with leaning is likely to be effective; and by 12 months they begin to perceive how this space may be extended by a mechanical aid.