These experiments compared the maximum displacement and disparity limits (Dmax) for apparent motion and stereopsis in random-dot displays in adult and 12–28 week-old infant subjects. Both stereo and motion Dmax increased during development, from about 0.3 deg in the youngest infants to 2 deg in adults. Some of the younger infants (12–14 weeks) did not give a stereo threshold, probably because stereopsis had not yet developed; but otherwise, the values of Dmax in the two domains were close to each other throughout the age range. These results suggest that both stereo and motion Dmax are limited by some common factor. Possible factors include receptive field sizes and internal noise. Simulations in which these were varied showed that while changes in both could contribute to the development of Dmax, only an increase in receptive field size can fully account for the rise in Dmax with age.