Theory of Mind Development in Swedish Preschoolers: Relations with Language, Executive function, Temperament, and the Social Environment

Abstract: Understanding others in social situations is a cornerstone of any lifespan. A part of social understanding comes from appreciating other’s intentions, desires, and knowledge, which can be called an understanding of others’ Theory of Mind. However, the measurement of Theory of Mind has predominantly been performed using cross-sectional designs and one type of Theory of Mind test, measuring false belief. Other alternatives that capture a scale measure of Theory of Mind better reflecting a continuum of development across a wider age range are now available. The current thesis investigates this scale longitudinally in relation to previously affirmed, but also less or unexplored, individual and social factors. In brief, the present dissertation finds limited support for individual but some support for social factors. The crucial finding is that Theory of Mind is only marginally related to the investigated factors, apart from Theory of Mind itself. Three studies support the conclusions put forth. Study I is a psychometric investigation of the Theory of Mind scale in Swedish preschoolers ages 3–5. The scale was psychometrically examined longitudinally as a 3- and 4-step scale in separate age groups (i.e., at three, four, or five years of age) and for boys and girls, respectively. The results showed that the scale was longitudinally consistent for both versions of the scale. Concerning the separate age groups, the scale was reliable as a 3-step scale in almost all investigated groups. However, the 4-step scale was only reliable when including all age groups (i.e., 3–5-year-old children). This suggests that Theory of Mind scales that include more than three steps might not be appropriate for all preschool ages. Study II predominantly investigated the Theory of Mind scale in relation to individual factors, namely executive function, productive language, and temperament. Socioeconomic status was included as a control variable. The individual factors related to Theory of Mind ability were executive function (when analyzed against the 3-step scale) and the temperament variable Shyness (both for the 3- and 4-step scales). Socioeconomic status was also related to ToM at three years of age. Study III investigated relations between ToM development and social factors: socioeconomic status, number of siblings, and parental use of mental state words (i.e., mention of cognition, emotion, or desire words). The children’s executive function and productive language were included as control variables. Parental use of cognition words was most often found to be related to Theory of Mind, but emotion and desire words were also related, to a lesser extent. In addition, the parents' frequency of spoken cognition words and emotion vocabulary size were related to a faster Theory of Mind development in children. Socioeconomic status and children’s productive language were also associated with ToM at four years of age. In summary, social factors received continued support as factors in Theory of Mind development. However, barely any individual factors surfaced in controlled analyses with Theory of Mind. With a specific focus on longitudinal studies of the development of children’s ability to understand other minds, the current thesis uniquely contributes to our understanding of Theory of Mind development in the preschool ages.