Research Article: Measuring Mentalizing Ability: A Within-Subject Comparison between an Explicit and Implicit Version of a Ball Detection Task

Date Published: October 10, 2016

Publisher: Public Library of Science

Author(s): Annabel D. Nijhof, Marcel Brass, Lara Bardi, Jan R. Wiersema, Tiziana Zalla.


The concept of mentalizing has been widely studied, but almost exclusively through tasks with explicit instructions. Recent studies suggest that people also mentalize on a more implicit level. However, to our knowledge, no study to date has directly contrasted the effects of implicit and explicit mentalizing processes on an implicit dependent measure within-subjects. We implemented this by using two versions of an object detection task, differing only on secondary catch questions. We hypothesized that if explicit mentalizing relies on complementary processes beyond those underlying implicit mentalizing, this would be reflected in enhanced belief effects in the explicit version. Twenty-eight healthy adults watched movies in which, during the first phase, both they themselves and another agent formed a belief about the location of a ball, and although irrelevant, these beliefs could influence their ball detection reaction times in the second phase. After this response phase, there were occasional catch questions that were different for the explicit and implicit task version. Finally, self-report measures of autism spectrum disorder (ASD) symptomatology were included, as the literature suggests that ASD is related to a specific deficit in implicit mentalizing. Both in the explicit and implicit version, belief conditions had a significant effect on reaction times, with responses being slower when neither the participant nor the other agent expected the ball to be present compared to all other conditions. Importantly, after the implicit version, participants reported no explicit mentalizing awareness. In our neurotypical sample, ASD symptoms were not found to correlate with either explicit or implicit mentalizing. In conclusion, the reaction time patterns in the explicit and implicit version of the task show strikingly similar effects of mentalizing, indicating that participants processed beliefs to the same extent regardless of whether they mentalized explicitly or implicitly, with no additional effects for explicit processing.

Partial Text

Theory of Mind (ToM; [1]), also called mentalizing, refers to the ability to attribute mental states (such as beliefs, desires and intentions) to oneself and others. It is needed in order to understand and predict other people’s behavior, and therefore it is thought to underlie all human social interaction [2]. The initial tests that were developed to measure ToM ability are false-belief tests such as the Sally-Anne task [3]. In these tasks participants are required to explicitly reason about the beliefs of another agent. Studies have shown that explicit mentalizing is cognitively demanding, as increased cognitive load and impaired executive functioning interfere with explicit belief reasoning [4–6]. Children are able to perform well on these mentalizing tasks only from about four years of age onwards [7]. Because of this, ToM was thought to be an ability that requires explicit reasoning, that is cognitively demanding and appears relatively late in a child’s development. However, two recent lines of research, discussed below, have questioned these features of ToM, which in turn has led to the claim that humans can also mentalize implicitly. An implicit form of mentalizing is thought to develop early and to be fast, cognitively efficient but inflexible, whereas explicit mentalizing processes would develop later and would be slower, more deliberate and flexible, but therefore also more cognitively demanding [8]. One line of argument for the existence of an implicit form of mentalizing comes from developmental studies. Several researchers have shown, by means of eye-tracking, that children show signs of tracking other people’s beliefs at a much younger age than four years [9–13]. In the study by Kovács and colleagues, infants as young as seven months old showed evidence of processing the true or false beliefs of an agent in a movie, since these beliefs affected their looking times to an object [13]. Given that these infants were obviously not instructed to track others’ beliefs, this can be taken as initial evidence for the existence of implicit mentalizing processes alongside, or instead of, the more established explicit mentalizing. In their study, the same paradigm was also applied to a group of adults, who showed a similar effect; in their case it was indicated by reaction times to the (expected or unexpected) presence of the object. In a different study, adults showed implicit processing through their eye movement patterns as well [14]. A second line of argument against a solely explicit definition of mentalizing can be found in the literature on autism spectrum disorder (ASD). The socio-communicative problems associated with this developmental disorder have often been explained in terms of deficits in ToM [15–17]. Still, two findings in the ASD population are inconsistent with this ToM deficit explanation, but the existence of implicit mentalizing may explain these inconsistencies. Firstly, explicit ToM ability develops around the age of four years [3], yet autistic symptoms are present in children at a much younger age [18]. Therefore, the socio-communicative impairment in ASD cannot exclusively be explained by an explicit ToM deficit. Implicit mentalizing is thought to be present at birth or to appear very early in development [8,19], hence a deficit in implicit mentalizing may explain early observed impairments in ASD [20]. Secondly, traditional ToM tests, such as first- and second-order false-belief tasks, are often passed by high-functioning children and adults with ASD (see [21], for an overview), despite the fact that they do experience severe difficulties with social cognition and mentalizing in daily life. Their successful performance on false-belief tests has been claimed to be dependent on compensatory strategies [22,23]. As implicit mentalizing is thought to act fast and inflexibly, it would offer fewer possibilities for such strategies. Indeed, recent findings in adolescents and adults with ASD suggest that ASD is related to a deficit in implicit mentalizing, even in the absence of explicit mentalizing problems [24–27]. This brings up an important point about the nature of implicit and explicit mentalizing processes. If a deficit in implicit mentalizing is possible without a deficit in explicit mentalizing, this seems to be in line with the suggestion that humans have two distinct systems for mentalizing (“two-system account”; [8,19,28]), and that both would have their own, perhaps partially overlapping, underlying neural architecture [29]. Still, studies investigating implicit mentalizing processes, and their similarities and differences to explicit processes, are relatively scarce, and from the above findings the question arises of whether there really are two separate systems for mentalizing. An alternative hypothesis, and one that we would like to investigate further in the current study, is that the mentalizing system is in principle implicit, and that on explicit tasks people simply recruit additional, non-mentalizing processes such as executive functioning and/or language skills [30], depending on the specific task requirements. This is also in line with the hypothesis that people with high-functioning ASD use their executive functioning skills to solve explicit ToM tasks in test situations, thus circumventing their mentalizing deficits [31]. In order to investigate whether two separable forms of mentalizing exist, what processes make them unique and during what kinds of tasks they are involved, research directly contrasting explicit and implicit mentalizing is needed [21]. The aim of the current study was to do just this, by comparing the effects of using implicit and explicit mentalizing processes directly, on the same (implicit) dependent variable and using a within-subjects design, thus circumventing the limitations of previous studies of implicit mentalizing. An important limitation is that most studies to date tested only implicit mentalizing and made no comparison with explicit mentalizing (e.g. [13,32]). Other studies did compare implicit and explicit mentalizing, but with tasks that were different in terms of the nature of the tasks themselves and/or the stimuli that were used (e.g. [24,25,27]), making it difficult if not impossible to attribute a differential pattern of results to the mere addition of explicit processes. In recent years, some attempts have been made to contrast implicit and explicit mentalizing on more comparable tasks [33,34], or even on the same dependent variable [35], and all these studies interpreted their results as evidence for the existence of two separate kinds of mentalizing.

All statistical analyses were conducted with IBM SPSS Statistics 20 (SPSS Inc., Chicago, IL, USA).

In recent years, evidence for an implicit form of ToM has been accumulating, and this has been taken as indirect evidence for a two-system account of mentalizing as proposed by Apperly and Butterfill [8]. However, direct comparisons of implicit and explicit mentalizing are scarce. Therefore, if mentalizing problems can be solved at an implicit level, it is still unclear what difference it would make to use explicit processing instead of, or on top of the implicit mentalizing processes. The current study was intended to make such a direct comparison, by testing the effects of implicit and explicit processing of beliefs on the same implicit dependent measure, using a within-subjects design.