Adjustment of reaching to change in object position by young infants

4-month-old infants manipulated and fixated an object less when it was presented in a new rather than a familiar place. Evidence was also found for persistence of manipulation and fixation at the empty place previously occupied by the object. At 5 months, changing the position of an object had no effect on the manipulation and fixation of the same infants, and there were no signs of persistence of manipulation and fixation at the object's original place. A comparison is made between these changes in reaching and changes in tracking behavior. 2 hypotheses are considered to account for these changes, 1 based on the development of an object concept and the other on improvement of motor skill.