Infants have an innate desire to form social bonds and jealousy protests are observed when an infant is trying to regain attention lost by a caregiver to a social competitor. The current study examined jealousy responses during the first year of life, between 6- to 9-months of age and 12- to 18-months of age, in response to loss of exclusive maternal attention, in addition to exploring implications for mother-infant attachment, EEG asymmetry, and cortisol reactivity and regulation. At both age groups, infants demonstrated increased approach behaviors when infants are faced with a social rival, in addition, left-frontal EEG asymmetry was associated with maternal-directed approach behaviors during the social rival condition. In the 6- to 9-month sample, left-frontal EEG asymmetry also demonstrated an association with infants regulatory abilities, measured by salivary cortisol. This study provides further evidence for the emerging links between social and emotional responses in infancy due to loss of exclusive maternal attention. / Includes bibliography. / Thesis (M.A.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection