Previous studies have shown that adults exhibit the strongest attentional bias toward neutral infant faces when viewing faces with different expressions at different attentional processing stages due to different stimulus presentation times. However, it is not clear how the characteristics of the temporal processing associated with the strongest effect change over time. Thus, we combined a free-viewing task with eye-tracking technology to measure adults' attentional bias toward infant and adult faces with happy, neutral, and sad expressions of the same face. The results of the analysis of the total time course indicated that the strongest effect occurred during the strategic processing stage. However, the results of the analysis of the split time course revealed that sad infant faces first elicited adults' attentional bias at 0 to 500 ms, whereas the strongest effect of attentional bias toward neutral infant faces was observed at 1000 to 3000 ms, peaking at 1500 to 2000 ms. In addition, women and men had no differences in their responses to different expressions. In summary, this study provides further evidence that adults' attentional bias toward infant faces across stages of attention processing is modulated by expressions. Specifically, during automatic processing adults' attentional bias was directed toward sad infant faces, followed by a shift to the processing of neutral infant faces during strategic processing, which ultimately resulted in the strongest effect. These findings highlight that this strongest effect is dynamic and associated with a specific time window in the strategic process.
Keywords: Attentional bias; Eye tracking; Facial expression; Infant faces; Time processing.
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