On Specifying Specificity: Facial Expressions at 4 Months.

Izard (2004/this issue) clarifies the position of differential emotions theory by proposing a distinction between hard and soft versions of event-emotion expression relations. We concur that the best design to examine situational specificity in facial expressions is one that utilizes multiple stimulus situations assessed over multiple occasions and ages. However, the problem of how to identify, a priori, a family of stimulus situations remains. We offer an example from our own recent work demonstrating how facial expressions and physiological indexes may converge to indicate the presence of a meaningful family of stimulus situations. Specifically, we found evidence for a family of frustrating, goal-blocking events that elicited expressions and cortisol responses indicative of anger at 4 months. Yet, individual differences exist in that these situations also elicited expressions and cortisol changes indicative of sadness. Identification of a more comprehensive set of such situations throughout infancy will allow researchers to more systematically examine the degree to which situational specificity of emotions is present.