Date of Award

Fall 11-26-2013

Degree Type


Degree Name

MS Experimental Psychology




Dr. Amy Joh

Committee Member

Dr. Kelly Goedert

Committee Member

Dr. Michael Lewis


sex differences, infants, still-face, socialization


Sex differences in human behavior have frequently been explored by researchers. Although there are numerous studies documenting sex differences between boys and girls from childhood into adulthood, few studies have adequately examined how genetics and environment interact in infancy to promote sex differences in infant behavior. Therefore, the present study sought to examine how sex differences in maternal behavior interact with differences in infant behavior. Maternal and infant behaviors were analyzed within the still-face paradigm, a paradigm which allows for examination of mother-infant interaction in normal, stressful, and recovery situations. It was hypothesized that infant boys would react with more negativity than girls to the stressful phases of the paradigm. It was also hypothesized that mothers would continuously treat their girl infants with more positivity, and maternal behavior would not be consistent across the phases of the still-face paradigm, ultimately becoming more negative by the end of the procedure. It was expected that these sex differences in maternal behavior, coupled with maternal increases in negativity, would translate to greater negativity in boys versus girls by the end of the procedure. Infant and maternal behavior was videotaped within the still-face paradigm and behaviors and facial expressions were later coded. All of the hypotheses were supported. Infant behavior differed by sex, with boys demonstrating more negative emotionality than girls in the recovery phase. Furthermore, mothers of girls treated their infants with more positivity than mothers of boys throughout the entire procedure. Maternal behavior also became more negative by the end of the procedure, which likely contributed to increased negativity seen in boys but not girls by the end of the procedure.

Approval.pdf (23 kB)