**Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect**

Takeo Tsujii and Kaoru Sakatani *Nihon University School of Medicine, Japan* 

## **1. Introduction**

34 Advances in Brain Imaging

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The course of dissociation for patients with borderline personality disorder and axis II comparison subjects: a 10-year follow-up study. *Acta Psychiatrica*  Recent neuroimaging studies have increasingly focused on the neural mechanisms of human deductive reasoning (see Goel, 2006 for recent review). Deductive reasoning is the cognitive process of drawing valid conclusions from a given set of premises. Although it should be performed independently of prior knowledge and intuitive beliefs, actual human reasoning often relies on them. Sometimes such beliefs provide valid solutions to problems, though they can also bias our judgment. This tendency toward bias in human reasoning has been experimentally studied through the demonstration of belief-bias effect in syllogistic reasoning (De Neys, 2006a, 2006b; Tsujii et al., 2006).

Belief-bias effect refers to the tendency of subjects to be more likely to accept the conclusion to a syllogism if they find it believable than if they disbelieve it, irrespective of its actual logical validity (De Neys, 2006a, 2006b; Tsujii et al., 2006). The experiment of belief-bias effect includes two types of syllogisms: one in congruent trials, in which the logical conclusion is consistent with beliefs about the world (valid-believable and invalidunbelievable), the other in incongruent trials, in which the logical conclusion is inconsistent with beliefs (valid-unbelievable and invalid-believable). A typical material design was presented in Fig.1. Belief-bias thus facilitates logical responses in congruent trials, while it opposes logically correct responses in incongruent trials (De Neys et al., 2008; De Neys & van Gelder, 2009b; Goel & Dolan, 2003; Tsujii & Watanabe, 2009, 2010; Tsujii et al., 2010a, 2010b, 2011).

One explanation for the belief-bias effect is offered by the dual-process theory of reasoning, which proposes the existence of two different human reasoning systems (Evans, 2003, 2008; De Neys, 2006a, 2006b). The first system, often called the heuristic system, tends to solve problems by relying on prior knowledge and belief. The second system, often called the analytic system, engages in reasoning according to logical standards. The schematic representation of the dual-process theory was presented in Fig. 2. The heuristic default system is assumed to operate rapidly and automatically, whereas operations of the analytic system are believed to be slow and heavily demanding of computational resources (De Neys, 2006a, 2006b; Tsujii & Watanabe, 2009, 2010). The aim of this chapter was to summarize the recent neuroimaging findings which supported the dual-process account of deductive reasoning, focusing on studies of the belief-bias effect.

Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect 37

hemoglobin (deoxy-Hb) have different absorption spectra in the infrared range, changes in concentrations of oxy- and deoxy-Hb can be calculated by detecting infrared light at two different wavelengths on the skull (approximately 787 and 827 nm). In general, enhanced oxy-Hb and reduced deoxy-Hb are associated with regional cortical activation. NIRS is noninvasive, robust against body movement and has been validated as a suitable technique for investigating neural mechanisms in psychological experiments (Tsujii et al., 2007, 2009a,

Although fMRI and fNIRS studies have provided interesting findings of the neural mechanisms of deductive reasoning, they can only examine correlations between cortical areas and a type of behaviour. The second aim of the present study was to demonstrate recent findings of rTMS studies in our laboratory which elucidated the roles of the inferior frontal cortex (IFC) and the superior parietal lobule (SPL) in human deductive reasoning (Tsujii et al., 2010a, 2011a). Especially, we adopted an off-line rTMS method in which lowfrequency rTMS is delivered to a specific brain area over several minutes to disrupt normal functioning of this area transiently after stimulation (Devlin et al., 2003; Hamidi et al., 2008, 2009; Hilgetag et al., 2001; Miller et al., 2008; Robertson et al., 2003). We investigated the effect of off-line rTMS of IFC and SPL on subsequent reasoning performance of congruent and incongruent trials. The rTMS approach can establish the causal relationships between

brain and behaviour more directly compared with fMRI and fNIRS.

Fig. 2. Schematic illustration of the dual-process theory

**2. fNIRS studies: Dual-task and time-pressure effects on reasoning** 

The dual-process theory claimed that the heuristic default system is assumed to operate rapidly and automatically, whereas operations of the analytic system are believed to be slow

2009b, 2010b, 2010c, 2011b).


Fig. 1. Material design of the belief-bias effect

Several neuroimaging studies using functional magnetic resonance imaging (fMRI) have examined the neural mechanisms of belief-bias reasoning (Goel, 2007). These studies reported that the belief-bias effect was associated with right inferior frontal cortex (IFC) activity (De Neys et al., 2008; Goel & Dolan, 2003). Right IFC activity was enhanced when subjects could respond correctly to incongruent reasoning trials. The authors of these studies claimed that the right IFC plays a role in inhibiting the default heuristic system for successful logical reasoning (De Neys et al., 2008; Goel & Dolan, 2003).

In general, the right IFC activity is known to play a central role in inhibitory function (Aron et al., 2004, 2007). For example, response inhibition has been found to be associated with the right IFC activity in several tasks, including the go/no-go task (Chikazoe et al., 2007, 2009; Chiu et al., 2008; Rubia et al., 2001; Tsujii et al., 2011b) and the stop-signal task (Aron and Poldrack, 2006; Hampshire et al., 2010; Rubia et al., 2001, 2003). Furthermore, when subjects changed from one task to another (task-set switching), the right IFC activity was also enhanced (Cools et al., 2002; Smith et al., 2004, 2006; Xue et al., 2008). In addition, other studies have suggested that the right IFC deficit may underlie the impaired response inhibition in patients with attention-deficit hyperactivity disorder (Durston et al., 2006, 2011; Rubia et al., 2005, 2010). These observations are consistent with the claims of dual-process theory that the right IFC plays a functional role in inhibiting the default heuristic system to enable analytic logical reasoning system activity (De Neys et al., 2008; Goel, 2007; Goel & Dolan, 2003). In the present paper, we further presented recent studies in our laboratory which examined the attention-demanding and time-consuming properties of the right IFC activity in belief-bias reasoning (Tsujii & Watanabe, 2009, 2010).

While most of the neuroimaging studies of deductive reasoning have used fMRI (Goel et al., 2000; Goel and Dolan, 2001, 2003; Knauff et al., 2002, 2003; Monti et al., 2007, 2009; Reverbeli et al., 2007, 2009, 2010), our laboratory utilized two relatively new imaging technique: one is functional near-infrared spectroscopy (fNIRS) and the other is repetitive transcranial magnetic stimulation (rTMS). fNIRS is the imaging technique for investigating cortical hemodynamic responses by measuring changes in the attenuation of near-infrared light passing through tissue. Since oxygenated hemoglobin (oxy-Hb) and deoxygenated

Several neuroimaging studies using functional magnetic resonance imaging (fMRI) have examined the neural mechanisms of belief-bias reasoning (Goel, 2007). These studies reported that the belief-bias effect was associated with right inferior frontal cortex (IFC) activity (De Neys et al., 2008; Goel & Dolan, 2003). Right IFC activity was enhanced when subjects could respond correctly to incongruent reasoning trials. The authors of these studies claimed that the right IFC plays a role in inhibiting the default heuristic system for

In general, the right IFC activity is known to play a central role in inhibitory function (Aron et al., 2004, 2007). For example, response inhibition has been found to be associated with the right IFC activity in several tasks, including the go/no-go task (Chikazoe et al., 2007, 2009; Chiu et al., 2008; Rubia et al., 2001; Tsujii et al., 2011b) and the stop-signal task (Aron and Poldrack, 2006; Hampshire et al., 2010; Rubia et al., 2001, 2003). Furthermore, when subjects changed from one task to another (task-set switching), the right IFC activity was also enhanced (Cools et al., 2002; Smith et al., 2004, 2006; Xue et al., 2008). In addition, other studies have suggested that the right IFC deficit may underlie the impaired response inhibition in patients with attention-deficit hyperactivity disorder (Durston et al., 2006, 2011; Rubia et al., 2005, 2010). These observations are consistent with the claims of dual-process theory that the right IFC plays a functional role in inhibiting the default heuristic system to enable analytic logical reasoning system activity (De Neys et al., 2008; Goel, 2007; Goel & Dolan, 2003). In the present paper, we further presented recent studies in our laboratory which examined the attention-demanding and time-consuming properties of the right IFC

While most of the neuroimaging studies of deductive reasoning have used fMRI (Goel et al., 2000; Goel and Dolan, 2001, 2003; Knauff et al., 2002, 2003; Monti et al., 2007, 2009; Reverbeli et al., 2007, 2009, 2010), our laboratory utilized two relatively new imaging technique: one is functional near-infrared spectroscopy (fNIRS) and the other is repetitive transcranial magnetic stimulation (rTMS). fNIRS is the imaging technique for investigating cortical hemodynamic responses by measuring changes in the attenuation of near-infrared light passing through tissue. Since oxygenated hemoglobin (oxy-Hb) and deoxygenated

successful logical reasoning (De Neys et al., 2008; Goel & Dolan, 2003).

activity in belief-bias reasoning (Tsujii & Watanabe, 2009, 2010).

Fig. 1. Material design of the belief-bias effect

hemoglobin (deoxy-Hb) have different absorption spectra in the infrared range, changes in concentrations of oxy- and deoxy-Hb can be calculated by detecting infrared light at two different wavelengths on the skull (approximately 787 and 827 nm). In general, enhanced oxy-Hb and reduced deoxy-Hb are associated with regional cortical activation. NIRS is noninvasive, robust against body movement and has been validated as a suitable technique for investigating neural mechanisms in psychological experiments (Tsujii et al., 2007, 2009a, 2009b, 2010b, 2010c, 2011b).

Although fMRI and fNIRS studies have provided interesting findings of the neural mechanisms of deductive reasoning, they can only examine correlations between cortical areas and a type of behaviour. The second aim of the present study was to demonstrate recent findings of rTMS studies in our laboratory which elucidated the roles of the inferior frontal cortex (IFC) and the superior parietal lobule (SPL) in human deductive reasoning (Tsujii et al., 2010a, 2011a). Especially, we adopted an off-line rTMS method in which lowfrequency rTMS is delivered to a specific brain area over several minutes to disrupt normal functioning of this area transiently after stimulation (Devlin et al., 2003; Hamidi et al., 2008, 2009; Hilgetag et al., 2001; Miller et al., 2008; Robertson et al., 2003). We investigated the effect of off-line rTMS of IFC and SPL on subsequent reasoning performance of congruent and incongruent trials. The rTMS approach can establish the causal relationships between brain and behaviour more directly compared with fMRI and fNIRS.

Fig. 2. Schematic illustration of the dual-process theory

## **2. fNIRS studies: Dual-task and time-pressure effects on reasoning**

The dual-process theory claimed that the heuristic default system is assumed to operate rapidly and automatically, whereas operations of the analytic system are believed to be slow

Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect 39

Behavioural analysis showed that the high-load secondary task impaired only incongruent reasoning performance. NIRS analysis found that the high-load secondary task decreased right IFC activity during incongruent trials. Correlation analysis showed that subjects with enhanced right IFC activity could perform better in the incongruent reasoning trials, though subjects for whom right IFC activity was impaired by the secondary task could not maintain better reasoning performance. These findings suggest that the right IFC may be responsible for the dual-task effect in conflicting reasoning processes. When secondary tasks impair right IFC activity, subjects may rely on the automatic heuristic system, which results in belief-bias responses. Tsujii & Watanabe (2009) therefore offer the first demonstration of

Tsujii & Watanabe (2010) addressed the difference in speed between the heuristic and analytic reasoning systems. The dual-process theory of reasoning explained the belief-bias effect by proposing a belief-based fast heuristic system and a logic-based slow analytic system. Although the claims were supported by behavioural findings that the belief-bias effect was enhanced when subjects were not given sufficient time for reasoning (De Neys, 2006b; Evans & Curtis-Holmes, 2005), the neural correlates were still unknown. Tsujii & Watanabe (2010), thus, examined the neural correlates of the time-pressure effect on the IFC activity in belief-bias reasoning using fNIRS. Subjects were asked to perform a syllogistic reasoning task, involving congruent and incongruent trials, both in long-span (20 s) and

Behavioural analysis found that only incongruent reasoning performance was impaired by the time-pressure of short-span trials. NIRS analysis found that the time-pressure decreased right IFC activity during incongruent trials. Correlation analysis showed that subjects with enhanced right IFC activity could perform better in incongruent trials, while subjects for whom the right IFC activity was impaired by the time-pressure could not maintain better reasoning performance. These findings suggest that the right IFC may be responsible for the time-pressure effect in conflicting reasoning processes. When the right IFC activity was impaired in the short-span trials in which subjects were not given sufficient time for reasoning, the subjects may rely on the fast heuristic system, which result in belief-bias responses. Tsujii & Watanabe (2010) therefore offer the first demonstration of neural

Behavioural Tsujii et al. (2010b) examined the difference in neural activity associated with deductive reasoning processes between young and older adults. Some behavioural studies reported that older adults exhibited a larger belief-bias effect than young adults (De Neys & Van Gelder, 2009), though the neural correlates of the aging effect on belief-bias reasoning remained unknown. Therefore, Tsujii et al. (2010b) examined IFC activity differences in belief-bias reasoning between young (mean age, 21.50 years) and older subjects (mean age,

Behavioural analysis found that older adults exhibited a larger belief-bias than young adults. Although the belief-bias effect was significant in both age groups, the size of the

correlates of time-pressure effect on the IFC activity in belief-bias reasoning.

neural correlates of dual-task effect on IFC activity in belief-bias reasoning.

**2.2 Belief-bias reasoning under time-pressure** 

short-span conditions (10 s).

**2.3 Aging and belief-bias reasoning** 

68.53 years) using fNIRS.

and heavily demanding of computational resources. Although these claims were supported by behavioural findings (De Neys, 2006a, 2006b), the neural correlates of dual-task and timepressure effect on belief-bias reasoning was unknown. Thus, a series of fNIRS studies in our laboratory examined the attention-demanding and time-consuming properties of the analytic reasoning system and IFC activity using fNIRS (Tsujii & Watanabe, 2009, 2010). In addition, we examined the aging effect on hemispheric asymmetry in IFC activity using fNIRS (Tsujii et al., 2010b).
