- Temperament
- Biologically rooted individual differences in emotional reactivity and self-regulation that are observable from early infancy. Thomas and Chess (1977) identified nine temperamental dimensions (activity level, rhythmicity, approach/withdrawal, adaptability, intensity, mood, distractibility, threshold, and persistence) and described three broad profiles: easy (~40%), slow-to-warm-up (~15%), and difficult (~10%). Kagan added the important concept of behavioural inhibition — a stable temperamental trait characterised by intense wariness in novel social situations, with biological correlates (amygdala reactivity, cortisol, heart rate) and longitudinal links to anxiety disorders.
- Goodness of fit
- Thomas and Chess's concept that developmental outcomes depend not on temperament alone, but on the match between a child's temperamental characteristics and the demands and expectations of the environment — particularly parenting style. A child with a difficult temperament raised by patient, responsive parents may develop well; the same temperament in an impatient, punitive environment predicts poorer outcomes. This concept shifted attention from temperament as a fixed destiny to the interaction between child characteristics and caregiving context.
- Social referencing
- The infant's use of a caregiver's emotional expression to regulate their own response to an ambiguous or uncertain situation. Emerges at around 8–9 months, coinciding with joint attention. Classic demonstration: Sorce et al. (1985) showed that infants looking across the visual cliff would cross the deep side if their mother posed a happy expression (74% crossed) but not if she posed fear (0% crossed). Social referencing is an early form of emotional communication that shapes fear learning, exploration, and the infant's understanding of which situations are safe.
- Emotional regulation
- The processes by which individuals influence which emotions they have, when they have them, and how they experience and express them (Gross, 1998). In infancy, regulation is initially external — co-regulated by caregivers through contact, vocal soothing, and contingent responding. As the prefrontal cortex matures, children progressively develop internal regulatory strategies: distraction, reappraisal, suppression. The quality of early co-regulation in the attachment relationship scaffolds the development of internal regulatory capacity. Poor regulatory development is a transdiagnostic risk factor across multiple forms of psychopathology.
- Theory of Mind (ToM)
- The capacity to attribute mental states — beliefs, desires, intentions, emotions, knowledge — to oneself and others, and to use these attributions to understand and predict behaviour. Typically assessed using the false-belief task (Wimmer & Perner, 1983; Baron-Cohen et al., 1985): children must predict where a character will search for an object given that the character holds a false belief about its location. Children typically pass at around 4 years. Autistic children often show delays on ToM tasks (Baron-Cohen's "mindblindness" hypothesis), though this account has been substantially nuanced by more recent research.
- Empathy and prosocial development
- Empathy involves both affective (feeling with another) and cognitive (perspective-taking) components. Zahn-Waxler and Radke-Yarrow (1992) demonstrated empathic concern and rudimentary prosocial responses — sharing, comforting — in infants as young as 14–18 months. Eisenberg's longitudinal research established that empathic concern combined with adequate emotional regulation predicts prosocial behaviour and positive social adjustment into adulthood. Children who are highly empathic but poorly regulated tend to become personally distressed rather than acting prosocially.
- Self-concept development
- Susan Harter's developmental model traces a shift from global, undifferentiated, and unrealistically positive self-perceptions in early childhood toward multidimensional, more accurate, and domain-specific self-evaluations in middle childhood and adolescence. Young children describe themselves in concrete, physical terms and show inflated self-perceptions because they cannot integrate contradictory self-relevant information. By 8–12 years, children use psychological trait terms, make social comparisons, and hold differentiated competence beliefs across specific domains (academic, athletic, social, physical appearance, behavioural).
- Self-conscious emotions
- Michael Lewis's term for emotions that require self-awareness and social comparison: shame, guilt, embarrassment, and pride. Unlike primary emotions (fear, joy, anger), self-conscious emotions require a representation of the self, knowledge of social standards, and an evaluation of the self against those standards. They emerge in the second year of life as self-representation develops. The shame–guilt distinction is clinically important: shame (global negative self-evaluation) is associated with psychopathology and aggression; guilt (focused on a specific behaviour) is associated with empathy and reparative action.