La. Symons et al., LOOK AT ME - 5-MONTH-OLD INFANTS SENSITIVITY TO VERY SMALL DEVIATIONSIN EYE-GAZE DURING SOCIAL INTERACTIONS, Infant behavior & development, 21(3), 1998, pp. 531-536
Infants' sensitivity to small shifts of gaze was assessed. An adult in
teracted with 5-month-olds then averted her eyes 5 degrees horizontall
y (infant's ear) or vertically (top of head or chin) while continuing
the interaction. Attention and smiling declined when the eyes were ave
rted horizontally but not vertically.