Browsing by Subject "Toddlers"
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Item Biosocial Influences on Toddler Gender-Linked Behavior(2012-02-14) Saenz, JanetThere is increasing evidence that biological factors (i.e., hormones) support the development of sex differences in behavior by organizing brain systems in prenatal life. However, the behavioral significance of the surge in reproductive steroids that results from the transient activation of the hypothalamic-pituitary-gonadal (HPG) axis around 3-months of age is largely unknown. The goal of the present study was to investigate the role of early postnatal activation of the HPG axis in the development of sex differences in human behavior. Participants included 54 children between 18 and 24 months (32 males and 22 females) and their parents. Infants and their caregivers participated in two, eight minute play sessions that were video-taped and later coded for children?s aggressive behavior and vocal ability. During each session, children wore an actigraph (Actiwatch, Philips Respironics) to provide a nonbiased assessment of activity levels. In addition, toddler?s temperament was measured using the Brief Infant Toddler Social-Emotional Assessment (BITSEA). Saliva samples from each infant were collected at 3-4 months of age and levels of testosterone were measured. Digit ratio levels were also measured at 3-4 months and used as a marker of prenatal androgen levels. The data indicated that boys were more aggressive, engaged in higher levels or activity, and showed less developed language ability. In addition, our results demonstrated that hormone markers associated with higher (i.e., more male-typical) testosterone were related to more aggressive behaviors, higher activity levels, expression of fewer total words, and a shorter duration of time spent vocalizing. A novel finding was that higher testosterone (i.e., more male-typical) levels in early postnatal life predicted less time spent vocalizing, for both sexes together and within males. The present research suggests that hormone levels in early postnatal life may contribute to the development of gender phenotypes, potentially making this a critical period for the development of language and other gender-linked behaviors.Item Mothers' emotions as predictors of toddlers' autonomous behaviors(2010-12) Bryan, Amy E.; Dix, Theodore H.; Anderson, Edward; Bigler, Rebecca; Hazen-Swann, Nancy; Jacobvitz, DeborahAutonomy is a critical component of early childhood with important implications for children’s competence and well-being (e.g., Erikson, 1963; Mahler, Pine & Bergman, 1975; Sroufe & Rutter, 1984). Although parental autonomy support is associated with the development of early autonomy (e.g., Endsley, Hutcherson, Garner & Martin, 1979; Frodi, Bridges & Grolnick, 1985; Landry, Smith, Swank & Miller-Loncar, 2000), the mechanisms underlying these associations are largely unexplored. Mothers’ emotions and the affective climate of parent-child interactions may be critical factors by which parenting influences early autonomy. This study (a) examined the degree to which discrete, naturally occurring maternal emotions regulate four indicators of autonomy during toddlerhood: co-regulated goal-directed behavior, low aimlessness, self-assertion, and positive initiative, (b) explored mechanisms through which maternal emotion exerts an influence on children’s autonomous behaviors, and (c) isolated the contribution of mothers’ emotions to children’s autonomous behaviors over that of mothers’ autonomy-supportive behavior. Several important findings emerged. First, maternal emotions, both felt and expressed, were related to children’s autonomous behaviors--mostly in ways predicted by emotion and relationship theories. In general, mothers’ frequent joy and infrequent anger, sadness, and fear predicted high autonomy. Second, the affective climate of mothers’ interactions with their toddlers predicted children’s autonomous behaviors over and above mothers’ autonomy-supportive behavior, suggesting that parental emotion is a unique aspect of autonomy support. Finally, different forms of early autonomy were predicted by different emotions in mothers, emphasizing the complexity of autonomy and the need to better define and measure this construct.Item Ontogeny of bipedalism : pedal mechanics and trabecular bone morphology(2013-12) Zeininger, Angel Diane; Shapiro, Liza J.A unique pattern of pedal loading from heel-strike at touchdown to hallucal propulsion at toe-off is a distinct feature of mature human bipedalism, however, its first appearance in the fossil record is debated. The main goal of this dissertation is to identify anatomical correlates to a modern human heel-strike, rigid foot, and propulsive hallucal toe-off. First, a biomechanical analysis of toddler walking is used as a 'natural experiment' to investigate the influence of non heel-strike (NHS, n = 11) and immature heel-strike (IHS, n = 7) on the location of the center of pressure and orientation of the ground reaction force resultant in relation to specific foot bones during stance phase. With an expanded knowledge of foot bone loading in toddlers, a microarchitectural approach is used to test the influence of a heel-strike, rigid foot, and propulsive hallucal toe-off on trabecular bone fabric properties in an ontogenetic series of human and African ape (chimpanzee, bonobo, and gorilla) calcanei, tali, first metatarsal heads and hallucal distal phalanges. This dissertation presents the first ontogenetic analysis of pedal trabecular bone in primates. Heel-strike and toe-off are developmentally independent from one another. Although most toddlers lack a hallucal toe-off, NHS and IHS apply equally high propulsive forces when the entire width of their forefoot is in contact with the ground. Biomechanical and fossil evidence suggest that a generalized active propulsion may have preceded the evolution of a propulsive hallucal toe-off. Although pedal trabecular fabric properties are more complex than predicted, trabecular correlates to heel-strike and hallucal toe-off are identified within adult human foot bones. Compared to toddlers and African apes, adult humans have a unique combination of relatively thick trabecular struts and an anteroplantar to posterodorsal primary trabecular orientation in the plantar aspect of the calcaneal tuber. In the calcaneal tendon volume of interest, adult humans have a unique anteroplantar to posterodorsal primary trabecular orientation associated with a propulsive hallucal toe-off. This dissertation provides the comparative context necessary to begin assessing the evolution and developmental timing of foot function and specific bipedal gait events in juvenile and adult fossil hominins.