Figure 2. Hypothesized developmental timelines.

Core processes (depicted in blue), object categorization (in green), and emotion understanding (in purple). The core processes belong to developmental cascades that might contribute to the development of categorization, including emotion categorization. At each point in time, multiple abilities are emerging; for example, at 9 months, infants may be crawling, are sensitive to contextual cues and functional inferences, and can match affective facial and vocal signals. Each of these reflect development within their own “domain” (e.g., colored row), but they may also reflect potential cascades across rows. For example, the limitations in the newborn visual system, which bias infants to look more at faces than at other stimuli, influence their developing perceptual abilities. Similarly, infants’ increased ability to interact with the world through visual-manual exploration provides them with opportunities to learn new properties of objects (e.g., their weight, how they sound when dropped), as well as to learn facial expressions, vocalizations, and other cues related to emotion during object explorations with caregivers and others. “Bias for stereotyped fear configurations” refers to the wide-eyed gasping face that is the stereotype in western cultures (for discussion, see Box 4).