PAPER One-month-old human infants learn about the social world while they sleep Bethany C. Reeb-Sutherland, 1 William P. Fifer, 2,3,4 Dana L. Byrd, 5 Elizabeth A.D. Hammock, 6,7 Pat Levitt, 8 and Nathan A. Fox 1 1. Department of Human Development, University of Maryland, USA 2. Department of Psychiatry, Columbia University, USA 3. Department of Pediatrics, Columbia University, USA 4. Developmental Neuroscience, Sackler Institute, USA 5. Department of Psychology, University of Florida, USA 6. Department of Pediatrics, School of Medicine, Vanderbilt University, USA 7. Vanderbilt Kennedy Center, Vanderbilt University, USA 8. Zilkha Neurogenetic Institute & Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, USA Abstract Although infants display preferences for social stimuli early in their lives, we know relatively little about the mechanisms of infant learning about the social world. In the current set of studies, 1-month-old infants underwent an adapted eyeblink conditioning paradigm to examine learning to both ‘social’ and non-social cues. While infants were asleep, they were presented with either a ‘social’ stimulus (a female voice) or one of two non-social stimuli (tone or backward voice) followed by an airpuff presented to the eyelid. Infants in the experimental groups displayed increased learning across trials, regardless of stimulus type. However, infants conditioned to the ‘social’ stimulus showed increased learning compared to infants conditioned to either of the non-social stimuli. These results suggest a mechanism by which learning about the social world occurs early in life and the power of ecologically valid cues in facilitating that learning. Introduction Much about how we think of infant abilities has changed since William James described their perception of the world as one of ‘blooming buzzing confusion’. We now know that even newborn infants are capable of associa- tive learning (for reviews, see Fitzgerald & Brackbill, 1976; Rovee-Collier & Lipsitt, 1982). Although such learning takes place within a social context very early in life, much of the research on infant associative learning has been conducted using non-social stimuli (e.g. a tone or light). There have been many studies on infants’ per- ception and discrimination of social stimuli (i.e. faces, voices), but it is unknown whether young infants who are challenged with an associative learning task will exhibit enhanced performance when exposed to social versus non-social stimuli. Newborns display heightened interest and attention toward social stimuli shortly after birth (Cassia, Simion & Umilta, 2001; DeCasper & Fifer, 1980; Goren, Sarty & Wu, 1975; Johnson & Morton, 1991; Macfarlane, 1975), suggesting that infants may have evolved over time to treat social stimuli in a privileged manner compared to other stimuli (Grossman & John- son, 2007). Studies that directly examined the role of context on learning within the first year of life have demonstrated that the social context influences language learning (Kuhl, Tsao & Liu, 2003) as well as the development of speech production (Goldstein, King & West, 2003). In addition, changes in social context can disrupt memory formation (Learmonth, Lamberth & Rovee-Collier, 2005) as well as learning to imitate a difficult task (Nielson, 2006). Within the first weeks after birth, most infants displayed conditioned learning to social stimuli, orienting toward an odor paired with touch (Sullivan, Taborsky-Barba, Mendoza, Itano, Leon, Cotman, Payne & Lott, 1991) and a tone paired with a face and voice (Koch, 1967). However, none of these studies directly compared the efficacy of non-social versus social stimuli on learning during early infancy. A robust learning paradigm that has emerged from the animal literature (McCormick, Clark, Lavond & Thompson, 1982; McCormick & Thompson, 1984) and has been used successfully in infants prior to 6 months of Address for correspondence: Bethany C. Reeb-Sutherland, Department of Human Development, Universityof Maryland, College Park, MD 20742, USA; e-mail: breeb@umd.edu Ó 2011 Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. Developmental Science 14:5 (2011), pp 1134–1141 DOI: 10.1111/j.1467-7687.2011.01062.x