| Because infant care is essential to human survival and reproductive success, it has been hypothesized that humans have evolved biological and cognitive mechanisms to facilitate adults' interest in and responsiveness to infants in ways leading to care-giving. Evidence for such mechanisms comes from studies showing that adults have attentional-emotional biases, and make distinctive physiological, neural, and hormonal responses, to infants, specifically to those physical features and behaviors that distinguish them from older humans. These biases also are normally stronger in women than in men, consistent with the hypothesis that women, due to their central role in infant care, have evolved a greater and more stable sensitivity to infants. However, despite evidence that infants constitute a special stimulus category, the nature of the cognitive mechanisms underlying interest in infants is still largely unexplored. This dissertation examines whether one such mechanism is visual attention toward infants, and, if so, how it is expressed (e.g., in overall looking time, face-recognition, and initial deployment of attention) and whether and how it is associated with adults' self-described interest in infants. Seven studies with young adults were conducted to address these questions. Studies 1-5 were preliminary and assessed the reliability/validity of three questionnaire-based measures of interest in infants and the characteristics of the sample of faces used in the main studies. Study 6, the first main study, used eye-tracking to measure subjects' visual attention while they viewed an adult face (a man or woman) paired with an infant face (a boy or girl). Subjects also completed the interest-in-infants questionnaires and a face recognition test. As indexed by the number and length of fixations, the results showed that women looked more at infant than at adult faces of either sex, whereas men looked more at infant faces only when paired with an adult male face. Women also reported greater interest in infants than men. The interest scores, however, were consistently associated with visual attention toward infants only for men (possibly due to a range restriction in women's interest scores). The results thus suggest that women's interest in infants as indexed by visual attention and self-report is more stable and higher than men's. Face recognition scores were not associated with interest-in-infants scores, perhaps because of the difficulty of the recognition task. Study 7, the second main study, examined whether infant faces have a greater effect than adult faces on the initial deployment of attention -- the so-called "prior-entry effect". The results suggested that infant faces do not have this effect or at least that it is smaller than that reported for other emotional stimuli, such as angry faces. There also was no association between individuals' point of subjective simultaneity and their self-reported interest in infants, consistent with the negative evidence from the prior entry task. The results thus suggest that the attentional and neural effects reported in other studies are unlikely to appear during the initial deployment of attention. Overall, the results suggest that women's interest in infants is more stable than men's, consistent with the hypothesis about the evolution of sex differences. They also show that oculomotor behavior can be successfully used to assess individual differences, including sex differences, in interest in infants. |
