Development of looking with head and eyes.

Research into stabilization of gaze has concentrated on how the eyes counterrotate to compensate for head rotation. There is little information on how head movements function as an integral part of gaze stabilization. The head and eye coordination of six adults and six infants was tested under two conditions: tracking a moving target when the body was stationary; fixating a stationary target when the body was turning. Under each condition, both infants and adults turned their heads more than their eyes in stabilizing gaze. The infants were tested at 3-week intervals between the ages of 11 and 28 weeks. During this period, the precision with which head turning was coupled to their own or the target movement developed to near adult level, showing rapid growth between 11 and 16 weeks. However, the infants' ability to couple the eyes onto the target did not change over the tested period, remaining much less precise than the adults'. These findings have important implications for the assessment of abnormal gaze stabilization, which could facilitate the early diagnosis of perceptuomotor dysfunction.