The development of visual preferences for direct versus averted gaze faces in infant macaques (Macaca mulatta)

Human and nonhuman primates show a preference for looking at faces with direct gaze. In humans, this preference emerges shortly after birth, but little is known about the development of gaze preferences in monkeys. This study tracked the development of gaze preferences in infant monkeys from birth through 6 months of age using infrared eye-tracking. Although absent in the first week, a strong significant preference for direct compared to averted gaze faces emerged rapidly, peaking around 2 months of age. When looking at the eyes, the monkeys' fixations were equivalent in duration for both gaze types in the first 2 months, but thereafter remained longer for the averted gaze faces. Therefore, the infants spent a greater proportion of time overall, but made shorter fixations, when looking at the direct compared to averted gaze faces. These results suggest that monkeys develop an efficient strategy when viewing the preferred direct gaze faces that involves longer viewing times, but shorter fixations.