On average, infants were 12.5 months old at the conclusion of the study, but depending on how many sessions they contributed, infants ranged in age from 11.5 to 14 months when the study ended. All SCH 900776 nmr infants were born at full term and were in good health. All families but one were urban and of middle to upper-middle socio-economic status. Both mothers and fathers had on average 17 years of education. Mothers’ average age at the start of the study

was 33 years; fathers’ average age was 35 years. Families were recruited to participate in the study by posting fliers about the research around the university where the research was conducted and by leaving fliers at healthcare centers. Participants were also recruited via “snowball” technique where participants mentioned the research via word-of-mouth to friends or contacts. Families received disks with the movies from each observation session and a children’s book as thank you gifts. Based on prior studies of hand and reaching preference in infancy, we used a semi-structured reaching procedure

at each session to test one- or two-handed reaching preference (e.g., Corbetta & Bojczyk, 2002; Corbetta & Thelen, see more 1999; Corbetta et al., 2006; Fagard & Lemoine, 2006; Hinojosa et al., 2003; Michel, Ovrut, & Harkins, 1985; Michel et al., 2002, 2006; Morange-Majoux, Pezé, & Bloch, 2000; Rönnqvist & Domellöf, 2006). The items used in the reaching task were a Fisher Price® two-part car and doll (7.5 cm long × 3.5 cm wide × 7 cm high), a plastic toy block with ribbons on top (5 cm long × 5 cm wide × 5 cm high), a plastic rattle (14 cm long × 14 cm circumference at the widest part × 3 cm wide at the handle), and a cup with a plastic egg inside (5.5 cm long × 5.5 cm wide × 6.5 cm high; see Figure 1). Because there is evidence that large objects provoke bimanual task performance in comparison with smaller objects, we chose objects that could feasibly be grasped with one hand to assess changes in reaching preference (see Greaves, Imms, Krumlinde-Sundholm, Dodd, & Eliasson, 2012 for a review). Infants

sat in a baby chair with a plastic tray. Before each presentation, we performed a check to ensure symmetrical body alignment of the trunk and hands to prevent any biases in reaching and acquisition Dimethyl sulfoxide of the toys (e.g., slightly turned to one side, one hand beneath the tray, etc.). The experimenter sat out of camera range to the side of the baby chair facing the infant. The camera was placed on a tripod, opposite the infant, at a distance of approximately 2 m. An experimenter presented each toy five times, for a total of 20 presentations per session (Tronick et al., 2004). Using Michel et al.’s (1985) procedure, we presented the objects in two ways: (1) three of the four toys were presented at midline directly in line with the infant’s nose so that the objects were equally accessible to each hand (e.g.