Lacan's concept of the mirror stage was strongly inspired by earlier work by psychologist Henri Wallon, who speculated based on observations of animals and humans responding to their reflections in mirrors. Wallon noted that by the age of about six months, human infants and chimpanzees both "seem" to recognize their reflection in a mirror. While chimpanzees rapidly lose interest in the discovery, human infants typically become very interested and devote much time and effort to exploring the connections between their bodies and their images. In a 1931 paper, Wallon argued that mirrors helped children develop a sense of self-identity. However, later mirror test research indicates that while toddlers are usually fascinated by mirrors, they do not actually recognize themselves in mirrors until the age of 15 months at the earliest, leading psychoanalytically trained critic Norman N. Holland to declare that "there is no evidence whatsoever for Lacan's notion of a mirror stage". Similarly, physician Raymond Tallis notes that a literal interpretation of the Lacanian mirror stage contradicts empirical observations about human identity and personality: "If epistemological maturation and the formation of a world picture were dependent upon catching sight of oneself in a mirror, then the stage theory would predict that congenitally blind individuals would lack selfhood and be unable to enter language, society or the world at large. There is no evidence whatsoever that this implausible consequence of the theory is borne out in practice."