Infants' recognition memory has been shown to be related to individual differences in look duration and level of heart period variability. This study examined the effect of individual differences in these 2 measures on infants' recognition of briefly presented visual stimuli using a paired-comparison recognition-memory paradigm. A sample of 35 full-term infants was studied longitudinally at 14, 20, and 26 weeks of age. Recognition memory for briefly presented stimuli was tested in 6 experimental conditions, with delays corresponding to different heart-rate-defined phases of attention. The 20-and 26-week-old infants, and infants with high levels of heart period variability, generally showed more evidence of recognition memory for briefly presented visual stimuli. Greater evidence of recognition memory was observed when stimuli were presented during sustained attention. Infants with more mature baseline physiological responses show greater evidence of recognition memory, and stimulus and procedural factors may be more important for the study of individual differences in infant visual attention than has previously been suggested.
2001 International Society on Infant Studies.