Modulation of saccade-rate in infants during their first year of life

As predominantly visual creatures, humans rely on visual exploration to study their environment. This behavior undergoes a substantial development during the first year of life, shifting from a disorganized sampling process to an organized, top-down-controlled one. Research on the development of visual exploration focused mainly on its spatial, rather than temporal aspects: where rather than when the eyes move. In adults, it is known that visual stimulation leads to an inhibition of saccades, followed by a large rebound of saccade rate before returning to baseline. The characteristics of this saccade-rate modulation are affected by both top-down and bottom-up factors. Here, we examine, for the first time, the developmental course of the temporal dynamics of saccade rate. In one experiment, three groups of participants, 3, 6, and 12 months old (N=20 each), were presented with black-and-white checkerboards, shortly followed by a video of a face. Findings showed that saccade rate was modulated in response to the checkerboard stimulus, in all three groups of infants. In contrast, the saccade rate was modulated by filmed faces only in infants 6 months old and above. In a second experiment, we presented 3 and 12-month-old participants (N=12 in each group), with black-and-white drawings of meaningful and abstract objects. Findings showed a pronounced modulation of saccade rate for both types of images in infants of both groups. An effect of object meaningfulness (higher rebound for meaningful vs. abstract objects) was found only for older infants. We conclude that the temporal modulation of visual exploration is present in very early infancy but only when stimuli are simple and of high contrast. Saccade-rate modulation reflects top-down recognition of semantic contents in 12-month-old, but not younger, infants. We suggest that studying saccade-rate modulation is a promising novel approach for studying the development of perceptual and cognitive processes in infancy.