Traditional studies on the developmental onset of jealousy, including classical studies on the developmental ontogeny of emotions (Bridges, 1932), studies of secondary emotions (Izard, 1977; Plutchik, 1980), emotions of self-awareness (Lewis; 1986), and studies of the first-born sibling’s triviality against later-born (Dunn & Kendrick, 1982) have all concluded that jealousy emerges around the second-birthday. However, recently, evidence from the “jealousy evocation” procedure, in which mothers attended exclusively toward a lifelike baby doll on their lap with positive emotions, while ignoring their infants (Hart & Carrington, 2002; Hart et al., 2004), have suggested that infants as young as 6-months express jealousy.
Although the discovery of infant jealousy is significant, above studies have failed to consider two important issues: Firstly, because jealousy is an emotion related to triangular relationships (White & Mullen, 1989), the jealousy evocation situation should be comparable with similar triangular relationships. However, in the above studies, the jealousy evocation situation has been compared with dyadic mother-infant situations, such as the mother reading a book, or a still-face perturbation. Secondly, whereas jealousy may be expressed directly toward the immediate unfaithful behavior of the beloved, it may also carry over to later dyadic relationships with the same person. However, the carry-over effect was not considered in the above studies.
Therefore, in this study, 12 seven- and ten-month-old infants and their mothers participated in a serial session consisting of four 3-minute situations: Mother-infant free-play (BL), Jealousy evocation (JE), Re-engagement during a second free-play (RE), and an Infant-mother-stranger situation (TR), in which mothers talked exclusively with a stranger, while ignoring the infants.
Results from a cross-context comparison between infants’ reactions to JE and TR indicated that in JE infants in both age groups stared fixedly at the mothers’ behaviors, but they were characteristically absorbed in self-regulation behaviors during TR. This tendency was clearer in older infants. These findings suggest that the infants differently discriminated between the two types of exclusion contexts, depending on the degree of threat to the relationship between them and the mother. That is, self-regulation behavior in TR appeared to be a situational response to fit their behavior to the context. The carry-over effect of JE was also clearly observed in RE. All infants showed eye-aversion when mothers tried to resume interactions. These findings suggest that infant jealousy may be observed more clearly as a carry-over effect in RE than in JE itself.
These findings should provide a new direction to studies on infant jealousy and lead to the re-consideration of the conclusions from recent studies suggesting that infant jealousy is differentiated by the expression of sadness in the jealousy evocation situation (Hart et al., 2004), as well as by the display of jealousy by infants between 3 and 6 months of age, when they were excluded in infant-mother-stranger triangular contexts (Legerstee et al., 2010).