Development of self-knowledge: Tactile localization to self-recognition
These two studies focused on the development of infants’ functional body knowledge. Many aspects of infant body knowledge have been researched extensively. For example, body parts are mapped onto the somatosensory cortex at least coarsely in infants as young as a few days old or older (Le Cornu Knight, Cowie, & Bremner, 2016; Milh et al., 2007). Infants also have some integration of sensory inputs and motor outputs, as evidenced by their ability to look toward the source of a sound during the first half-year of life (Ashmead, Davis, Whalen, & Odom, 1991; Morrongiello, Fenwick, Hillier, & Chance, 1994). Additionally, infants have some knowledge of body structure, as they can detect discrepancies in the arrangement of the configuration of these body parts and distortions in body part size as early as 3.5 months of age (Zieber, Kangas, Hock, & Bhatt, 2015). Most previous research has focused on nervous system structure, knowledge of body structure, or reactive responses to the environment. Less is known about the development of the agentive response of infants localizing targets on their bodies. In a longitudinal study, vibrating targets were placed on eight different face locations approximately every other week starting as young as 2 months of age to test the development of infants’ ability to reach to targets on the surface of the body. The primary findings were that the ability to reach to targets on the face improved with age, and infants could reach to the mouth earlier than the other face locations. In a second study, these infants then received additional experience with a visual-proprioceptive-tactile contingency in the mirror, which accelerated mirror self-recognition relative to two control group.