Lifespan Theory of Mind

While on a plane, you notice your seatmate looking out the window. What is she thinking? Is she worried about the flight or eager to arrive in a new location? Researchers refer to such mentalizing as theory of mind (ToM). We use ToM to explain and predict our own and others’ behavior based on mental states such as beliefs, knowledge, intentions, and desires. ToM research has increased steadily since Premack and Woodruff (1978) introduced the term. A quick Google Scholar search for “theory of mind,” with citation to Premack and Woodruff (run December 7, 2017) yielded 5,940 papers. This conservative estimate does not include ToM’s many aliases, including mentalizing, mind-reading, and mental-state reasoning.

Early ToM research focused mostly on preschoolers’ understanding of false belief. For example, show a child a crayon box, and ask her what’s inside. Once she says “crayons,” open the box to reveal ribbons. Close the box and ask, “When I first showed you this box, what did you think was inside?” Young preschoolers say “ribbons.” Ask them what another person will think is inside and, again, they’ll say “ribbons.” By around 4.5 years of age, children say “crayons” when asked these questions. This dramatic shift in responding indicates that ToM becomes fully elaborated at around 4.5 years of age (see Wellman, 1990; Wimmer & Perner, 1983). In the crayon-box task, children must ignore their knowledge of reality (there are ribbons in the box) to understand what they first thought or what a naïve other would think is inside (crayons).

A 2005 study reporting false-belief understanding in infants challenged the idea that this concept develops around age 4, ushering in a torrent of work on infant false-belief reasoning (Onishi & Baillargeon, 2005). This work incorporates implicit measures such as anticipatory eye gaze and looking time. Presently, the ToM literature can be divided into age-related groups. Most work is on preschoolers, but there is growing work on infants and older adults. There is relatively little work on older children and younger adults; most of the latter work involves neuroatypical individuals (e.g., those with autism, schizophrenia). There is also ample literature on non-human ToM (see Heyes, 2015).

From a lifespan perspective, the human ToM literature shows possible ToM in infants (at least at an implicit level), marked ToM improvements from 3 to 5 years of age, gradual ToM improvements throughout adolescence, relatively stable ToM in younger adults, followed by gradual ToM decline in older adulthood (Miller, 2012). This developmental picture rests mostly on cross-sectional research using age-appropriate tasks. ToM research would benefit from using the same tasks across age groups. Examples include nonverbal false-belief tasks, and tasks permitting continuous rather than discrete measurement of ToM (e.g., Kovács, Téglás, & Endress, 2010; Sommerville, Bernstein, & Meltzoff, 2013).

Most researchers agree that ToM develops in early childhood, or perhaps even infancy. Most researchers also agree that ToM continues to develop beyond early childhood. What we don’t know is how ToM develops, changes, and expresses itself after early childhood and across the lifespan. Indeed, even high-functioning adults occasionally make ToM errors when reasoning about naïve minds. Some have compared ToM to a tool that one has and may use, but not always use properly (Keysar, Lin, & Barr, 2003).

The collection of papers in this topical issue of Zeitschrift für Psychologie reflects the diversity of ToM research that uses different ages, populations, and methods. The issue’s six articles comprise two review articles, two original articles, and two opinion pieces.

Derksen, Hunsche, Giroux, Connolly, and Bernstein (2018) systematically review longitudinal ToM research. After failing to find suitable studies on adults, the authors focus on children. Their review identifies several precursors to ToM development, including cognitive abilities (e.g., attention skills, executive function, and language ability) and behavioral experiences (e.g., quality of interaction with parents and older siblings). The authors call for longitudinal studies of ToM in younger and older adults.

Marchetti, Manzi, Itakura, and Massaro (2018) focus on human – robot interaction, and discuss its roots in philosophy, mainstream literature, film, and the scientific literature. The authors note how humans of all ages ascribe mental states to robots. Marchetti and colleagues pose and ponder heady questions about humans’ interaction with increasingly complex machines. The authors conclude that the more human a robot appears and acts, the more “like me” we view and treat it.

Rafetseder and Perner (2018) report a robust correlation between counterfactual (“what if”) reasoning and ToM in a sample of 3- to 7-year-old children. Testing predictions according to three theories, the authors find support for a teleological theory showing that counterfactual reasoning is an integral part of belief attribution. The data also show that mastery of counterfactual reasoning and belief attribution develop gradually, implying development “far into an individual’s life.” (p. 110).

Lagattuta, Tashjian, and Kramer (2018) test associations among age, executive function, and what they call “life history ToM”: recognition that prior life experiences influence how individuals think, feel, and make decisions about the future. By presenting stories in which characters have positive or negative interactions on two occasions, the authors find that age and executive function independently predict higher life history ToM in 4- to 10-year-old children and adults.

Finally, Mahy (2018) and Wellman (2018), respectively, opine from a junior- and senior-career perspective. They each highlight directions for future research. Mahy calls for more (1) lifespan developmental work on affective ToM and (2) studies of individual differences in older adults’ ToM. Wellman calls for more (1) developmentally-sensitive measures, such as multi-item ToM scales for children and adults and (2) studies of how humans understand ordinary and extraordinary (e.g., robot) minds.