Working together to orient faster: The combined effects of alerting and orienting networks on pupillary responses at 8 months of age.

Multiple visual attention mechanisms are active already in infancy, most notably one supporting orienting towards stimuli and another, maintaining appropriate levels of alertness, when exploring the environment. They are thought to depend on separate brain networks, but their effects are difficult to isolate in existing behavioural paradigms. Better understanding of the contribution of each network to individual differences in visual orienting may help to explain their role in attention development. Here, we tested whether alerting and spatial cues differentially modulate pupil dilation in 8-month-old infants in a visual orienting paradigm. We found differential effects in the time course of these responses depending on the cue type. Moreover, using Principal Component Analysis (PCA) we identified two main components of pupillary response, which may reflect the alerting and orienting network activity. In a regression analysis, these components together explained nearly 40 % of variance in saccadic latencies in the spatial cueing condition of the task. These results likely demonstrate that both networks work together in 8-month-old infants and that their activity can be indexed with pupil dilation combined with PCA, but not with raw changes in pupil diameter.