Sensorimotor activity is important to the processes by which infants acquire knowledge from the environment. In this study, infants' reaching behavior to moving objects in the light and dark was used to evaluate 4 components of perceptual-motor processing: attention/motivation (number of reaches); speed of processing (time to achieve contact); auditory localization(number of misses); object recognition (number of closed grasps on first contact). Subjects included 18 term infants (7.5 to 8.5 months); 8 exposed to cocaine and/or opiates in utero (EXP) and 10 nonexposed (NONEXP). Sixteen trials were presented to the infants in which 4 objects emitting sounds moved clockwise into the infant's reaching space in the light and dark. The session was videotaped using infrared sensitive cameras for later coding of reaching activity by research assistants masked to the exposure status of the infants. Compared to the light condition, both groups reached and contacted the object less often, missed more often, and took longer to contact the object in the dark (P<.01 in all cases), reflecting the difficulty of the task when only auditory cues were available to elicit and guide reaching. In both the light and dark, object contacts made with a closed grasp were significantly faster than those involving open-handed touches(P<.05). While both groups reached for the object equally often in the light, EXP infants reached less than NONEXP infants in the dark(P<.05). When a reach was made, however, both groups missed the object equally often in the light and dark. While the time to contact the object was similar in both groups in the light, EXP infants were significantly slower to make contact with the object in the dark compared to NONEXP infants(P<.05). Both groups used a closed grasp equally often in the light, however EXP infants were more likely to use a closed grasp in the dark(P<.05). In sum, the reaching behavior of EXP infants did not differ from NONEXP infants when the task was relatively easy, but EXP infants showed less engagement in sensorimotor activity when the task was more demanding. Given that EXP infants localized objects as well as NONEXP infants when they tried, the decrement in reaching behavior may reflect attentional or motivational deficits that could affect the cognitive development of EXP infants.