The role of control functions in mentalizing: Dual-task studies of Theory of Mind and executive function

Abstract

Conflicting evidence has arisen from correlational studies regarding the role of executive control functions in Theory of Mind. The current study used dual-task manipulations of executive functions (inhibition, updating and switching) to investigate the role of these control functions in mental state and non-mental state tasks. The ‘Eyes’ pictorial test of Theory of Mind showed specific dual-task costs when concurrently performed with an inhibitory secondary task. In contrast, interference effects on a verbal ‘Stories’ task were general, occurring on both mental state and non-mental state tasks, and across all types of executive function. These findings from healthy functioning adults should help to guide decisions about appropriate methods of assessing ToM in clinical populations, and interpreting deficits in performance in such tasks in the context of more general cognitive dysfunction.

Introduction

Theory of Mind (ToM) is the ability to interpret another’s mental states – encompassing desires, beliefs, and intentions – which may conflict with the observer’s own knowledge or with reality. Effective ToM skills are important for normal social functioning (Baron-Cohen, 1995) because they underlie the understanding of others’ behaviour. An important set of cognitive processes supporting ToM skills are executive functions (EFs, see Perner & Lang, 1999 for a review), which include cognitive control mechanisms such as attentional flexibility, inhibition of prepotent information, and updating information in working memory (e.g., Miyake et al., 2000). Early conceptions of ToM emphasised the modular, domain-specific social processing involved, excluding the involvement of domain-general processes such as EFs, at least in adults (Baron-Cohen, 1995, Fodor, 1992, Leslie, 1994). More recent literature has argued that social understanding is likely to involve both modular processes and domain-general processes such as EFs (e.g., Leslie et al., 2004, Leslie et al., 2005).

Previous studies investigating the link between ToM and EFs have analysed correlations between the two types of task, or patterns of impairment in populations with poor social functioning. Children with autism or Aspergers Syndrome have difficulty interpreting cues to mental state (e.g., Baron-Cohen, 1995, Happe, 1994), whilst being unimpaired on matched tasks with similar EF demands but with no requirement to understand mental states (e.g., Charman and Baron-Cohen, 1995, Leslie and Thaiss, 1992). Studies with older adults reveal that whilst there are well-replicated age-related declines in EFs (e.g., MacPherson et al., 2002, Wecker et al., 2000), the effects of age on ToM tasks are unreliable: some studies indicate decline in ToM (e.g., Maylor, Moulson, Muncer, & Taylor, 2002), others stability (e.g., MacPherson et al., 2002) or advantage (Happe, Winner, & Brownell, 1998) with age. Maylor et al. (2002) showed that despite age-related decline in both ToM and EFs in the same sample, there was no relationship between the two impairments. Also, patient studies show spared ToM skills in the presence of EF impairments (Bird, Castelli, Malik, Frith, & Husain, 2004), poor mental-state reasoning in the presence of spared EF skills (Fine et al., 2001, Lough et al., 2001) or preserved ToM impairments when EF skills were covaried (Rowe, Bullock, Polkey, & Morris, 2001). These findings indicate independence of ToM and EF skills. However, as noted by German and Hehman (2006), these studies may underestimate fractionation within executive processes, so finding an association between ToM and EF may depend on the measures chosen.

A number of studies have challenged the modular view of ToM, based on evidence of relationships between ToM and EF performance in typically developing and autistic children (e.g., Carlson et al., 2002, Hughes, 1998, Hughes et al., 1994, Ozonoff et al., 1991, Sabbagh et al., 2006, Zelazo et al., 2002). German and Hehman (2006) found evidence from an aging sample for common processing in ToM and EF tasks, with age-related declines in reasoning both about mental and non-mental states overlapping statistically with decreased inhibitory control. Incrementing the executive demands of ToM tasks increased the magnitude of age deficits (see also McKinnon & Moscovitch, 2007). Finally, lesion and neuroimaging studies indicate that the prefrontal cortex is involved in both EFs and ToM (e.g., Channon and Crawford, 2000, Fletcher et al., 1995, Sabbagh, 2004, Stone et al., 1998, Stuss et al., 2001), suggesting that both processes may depend on a common neuroanatomical system. However, Apperly, Samson, and Humphreys (2005) note that many neuropsychological studies fail to separate belief reasoning from other processes necessary for completion of these tasks, raising doubts about strong claims regarding domain-specificity of ToM.

The current study utilises dual-task methodology with healthy adults to investigate the resource overlap between ToM tasks and EF. Using dual-task methodology, McKinnon and Moscovitch (2007) found that concurrent performance of an updating task impaired answering both first- and second-order ToM questions, with greater interference for the more complex second-order questions. However, this study did not include control non-mental state tasks, and so the specificity of the role of updating in ToM cannot be determined. Also, the role of other EFs such as inhibition and switching attention remains unexplored.

Although ToM has often been considered a unitary construct, it is likely that different methods of assessing social understanding place different demands on EFs. For example, Lough et al. (2006) found statistical overlap between EF and a ToM stories task, but not with a cartoon test of ToM. The current study examined two of the most widely used ToM tasks in adult populations. Stories tests of ToM (e.g., Channon and Crawford, 2000, Happe, 1994, Stone et al., 1998) assess understanding of faux pas, double bluffs, mistakes, and white lies, and typically involve considering the mental states and related behaviours of multiple characters, which might include false beliefs. In contrast, the Mind in the Eyes Test (Baron-Cohen, Wheelright, Hill, Raste, & Plumb, 2001) requires recognition of emotional states from pictures of eyes, and does not require coordination of multiple perspectives or the integration of mental states with behaviours.

Most studies examining the relationship between EF and ToM have used complex EF tasks that load multiple control skills. We aimed to delineate more precisely the nature of EF involvement in ToM tasks by administering separate tasks of inhibition, switching, and updating. Three issues will be investigated. First, if Eyes and Stories ToM tasks depend upon the same pool of cognitive resources as a range of EFs, there will be dual-task interference when a ToM task is performed concurrently with an EF task. Second, if interference between ToM and EF tasks is specific to interdependence between these two processes, dual-task costs should be present only when EF tasks are performed in combination with ToM items, and not in combination with non-ToM items. Third, to determine whether ToM tasks depend on specific EFs (inhibition, switching or updating) dual-task costs under separate EF secondary task conditions were examined, including a control condition which was attentionally demanding but had minimal EF load.