Courage, M.L., Reynolds, G.D., & Richards, J.E. (2006). Infants' visual attention to patterned stimuli: Developmental change and individual differences from 3- to 12-months of age. Child Development, 77, 680-695. (PDF)
To examine the developmental course of look duration as a function of age and stimulus type, infants aged 14-, 20-, 26-, 39-, and 52 weeks were shown static and dynamic versions of achromatic geometric stimuli, faces, and Sesame Street material for 20 seconds of accumulated looking. As duration of a look does not reflect a unitary attentional process but can be parsed according to corresponding heart-rate defined phases (i.e., stimulus orienting, sustained attention, attention termination), infants’ HR change was also measured. Analysis of the look duration data indicated that prior to 26 weeks, infants’ looks decreases linearly for all stimuli. For the older infants, look durations continued to decline for the geometric patterns but increased for the Sesame Street and face stimuli. On-line measures of heart-rate confirmed this greater engagement with the more complex stimulus types. Individual differences in look duration and baseline heart rate variability were independently related to stimulus type. Infants with short look durations and those with high heart rate variability showed larger HR decelerations in sustained attention to Sesame Street and face stimuli than to the achromatic geometric patterns. Infants with long look durations did not differ in their deceleration to the stimulus types and also spent more time in the phase of attention termination relative to phases of orienting and sustained attention. The results suggested that short lookers and those with high HRV showed greater engagement with complex stimuli that did long lookers and those with low HRV.