Visually elicited finger movements in infants.

The relationship between visual stimulus intensity and finger movements was examined in infants from 10 to 15 weeks of age and from 20 to 25 weeks of age who were shown a cone that varied in size, brightness, and distance from them. 2 hypotheses derived from Schneirla's approach-withdrawal theory were examined; (1) that responses of the younger infants would be directly related to stimulus intensity, with finger extension (approach) movements elicited by weak stimuli and flexion (withdrawal) movements elicited by more intense stimuli; and (2) that stimulus dimensions such as distance, size, and brightness would make additive contributions to stimulus intensity, so that combinations of weak intensity would elicit finger extension and combinations of strong intensity would elicit flexion. Analyses of variance indicated no significant main effects of distance, size, or brightness, but significant age, intensity, and age x intensity effects. Older infants tended to extend their fingers more than younger infants. However, as intensity increased, the younger infants' responses showed decreases in extension and increases in flexion, while the older infants' responses indicated no clear relationship between intensity and response direction. That younger infants were responsive to the quantitative rather than the qualitative aspects of stimulation has important implications for understanding how various stimulus dimensions affect infant responses.