Eyes play a prominent role in our daily social encounters and are sometimes metaphorically referred to as windows to our souls. There now is compelling evidenceto support the notion that much information about another person’s mind can be gleaned from his or her eyes. In one proof of concept, the Reading the Mind in the Eye Test (RMET), developed by Simon Baron-Cohen and his group at Cambridge University in the UK, has documented our ability to identify inner states from the eyes and the region surrounding the eyes. The extent of information that eyes communicate about other minds might be somewhat limited, yet evidence argues against the longheld view of philosophers in the skeptical tradition that the contents of other minds cannot be directly observed. Instead, human eyes form a bridge between self and other by providing direct access to another person’s inner state.
The phenomenon is unique to humans alone. Indeed, after comparison with nearly half of all primate species, the human eye has been shown to be morphologically and responsively unique. Humans not only show the greatest horizontal elongation of the eye outline and the largest amount of exposed tissue (called sclera) around the eyeball, but are also the only species with sclera that is white. When compared with our closest living primate relatives, chimpanzees, we humans focus more steadily on the eye region when scanning faces. By 14 months of age, the human gaze follows eyes almost exclusively whereas other great apes rely more on head direction.
The sensitivity to eyes emerges early in human development. From birth, newborn infants show a preference for faces, despite their poor visual acuity. Human infants prefer to look at faces that have eyes open versus eyes closed. Newborns exhibit a preference for faces only with naturally appearing eyes, including black iris and white sclera, versus control faces with white iris and black sclera. And infants appear to glean emotional information about other minds by gazing at eyes, literally recruiting brain regions that, in adults, are involved in understanding another person’s mental state. Strikingly, by seven months of age, infants detect emotional cues and distinguish between direct and averted gaze solely on the basis of the eye whites.