## 2 ACT-R Modeling for Task Switching
### Symbolic Structure of Proposed Task Switching Model  
According to the abovementioned accounts of task switching, a symbolic representation of the cognitive process of task switching by self-interruption was framed based on ACT-R, consisting of three stages, as shown in Figure 2.  
The first stage is based on the property of task switching related to the account that self-interruptions can be triggered by emotions experienced when there is an imbalance between the difficulty of an ongoing task and the performer's ability [16]. Additionally, several neuroscience studies [35,36] have shown that the experienced emotions have affective values that influence the cognitive process in decision making under situations where the orbitofrontal cortex plays a key role in neural functions between emotion and decision making and has a neural interconnection with the basal ganglia, represented by the ACT-R procedural module (see Figure 3). In particular, the procedural module includes the role of the striatum in the basal ganglia, which performs the pattern-recognition of information required to determine the next action [7], and the striatum to which the cortical regions corresponding to ACT-R buffers project is known to have a direct interconnection with the orbitofrontal cortex. Together, the emotions experienced during the imbalanced state can be interpreted as directly influencing the cognitive process that determines the next action in the basal ganglia via the neural functions in the connection between the orbitofrontal cortex and the basal ganglia. In other words, the orbitofrontal cortex can affect  
Figure 1: Schematic diagram of the ACT-R cognitive architecture. The neural location of the modules and buffers are indicated in parenthesis. the selection of the next action associated with self-interruption by projecting the affective value of emotion experienced by the imbalance in the basal ganglia. Therefore, in this study, based on the procedural module representing the basal ganglia, which has a direct interconnection with the orbitofrontal cortex in cognitive decision making, a procedural rule was defined; the rule is selected when there is an affective value derived from the imbalanced state and includes the action related to self-interruption. This rule is depicted in the interrupt-task stage in Figure 2, and a verbal description of the rule in pseudo-English form is given as Algorithm 1:  
```
ifgoal is to perform the ongoing task,  and there is an affective value from an imbalance state then  clear the imaginal buffer endif
```  
**Algorithm 1** INTERRUPT-TASK rule  
The interrupt-task rule is implemented when there is an affective value for which the imaginal buffer is cleared to indicate that the ongoing task is self-interrupted. The imaginal module is used to store intermediate information that is necessary for performing a task [37]; thus, clearing the information necessary for the ongoing task interrupts the  
Figure 3: Simple schematic diagram of the basal ganglia interconnected with the anterior cingulate cortex (ACC), the dorsolateral prefrontal cortex (DLPFC), the ventrolateral prefrontal cortex (VLPFC), and the orbitofrontal cortex (OFC) associated with processes of decision-making. Figure 2: Symbolic structure of task switching. task. The affective value projected to the basal ganglia from the orbitofrontal cortex is represented by several subsymbolic equations that quantitatively evaluate the imbalance between the difficulty of an ongoing task and the performer's ability. Additionally, in this model, the subsymbolic equations are implemented in the procedural module, which has a direct connection with the orbitofrontal cortex, because the existing ACT-R has no module that directly represents the orbitofrontal cortex associated with emotion. In the second stage, it is decided whether another task is to be performed or the ongoing task is to be continued, where the imaginal buffer is cleared to represent the self-interruption in the previous interrupt-task stage.