Developmental changes of oculomotor characteristics in infants when awake and in the 'active state of sleep'.

Since the principal criterion for identifying sleep in the young infant is eye closure, a study was undertaken to ascertain whether fast or 'saccadic-type' movements which occur in the eyes-closed condition differ in any respect from those which are observed in the eyes-open (awake) state. Specific parameters included the amplitude-velocity relationship, the numbers and types of non-conjugate movements (disjunctive and monocular), directionality and densities (EM/min). Measurements were made on 12 infants at 4-week intervals as they progressed in age from 4 weeks to 12 weeks. The results disclosed that in the main as the infants developed, a change, if any, of ocular characteristic in the awake state was paralleled by a similar change in the eyes-closed state, although the absolute number of eye movements was higher in the eyes-open state compared to the eyes-closed state. This suggests that the eye movement characteristics, whether the eyes were open or shut, were dictated primarily by oculomotor development and the mechanics of eye closure rather than by different mechanisms of neural control effected through different states of consciousness. Of special interest was the finding that the velocity-amplitude relationship in the infant's eyes-open state was almost identical to that reported for adults in the eyes-open state whereas the value for the eyes-closed state was comparable to that of the adult's eyes-closed awake state rather than to the value obtained for adults in REM sleep.