Macaques but not lemurs co-orient visually with humans.

The ability to engage in visual co-orientation (VCO) is suggested by naturalistic observations of primates, but experimental comparisons of different species are lacking. This study compared the propensity of lemurs (Eulemur macaco) and macaques (Macaca arctoides) to engage in VCO, defined as turning to look in the same direction as another individual whose focus of attention changes. The macaques consistently showed VCO whereas the lemurs showed no such response. This species difference has implications for understanding the evolutionary origins of more advanced abilities that build upon VCO, such as shared visual attention and theory of mind.