Tonic and phasic orientation in full-term and preterm infants.

Thirty-three full-term infants and thirty-eight preterm infants (on average born at 30 weeks gestation) were tested for their latency to turn toward checkered stimulus patterns (phasic orienting or "attention-getting") and for the duration of their initial fixation (tonic orienting or "attention-holding"). Plotted against the logarithm of the subjects' postconceptional age, turning latency fell linearly between 36 and 120 weeks, while fixation time fell abruptly at 53 weeks. Preterm and full-term infants showed the same developmental trends, implying that both of these attentional behaviors are biologically timetabled and that neither is greatly affected by premature extrauterine experience. Unexpectedly, phasic orientation in the first 30 postnatal days was significantly faster in preterm than in full-term infants, and fixation times failed to differ. Despite the necessary functional integration of phasic and tonic orienting in mature visual scanning and attention, the present results suggest an independence in their early postnatal development and that neither is mature at birth.