The Cognitive And Neural Mechanisms Of Task Dominance Affecting Task Switching

Task switching refers to the cognitive process that flexibly switches among different tasks.Task switching reflects the individual cognitive flexibility,which is a vital ability for us to accommodate to the society.However,how could people switch between tasks,which factors may affect the process of task switching? The research on task switching could help us better understand the human cognitive flexibility and goal-directed behaviors.The task switching paradigm provides a laboratory tool for studying the psychological mechanisms behind task switching.In the paradigm,participants are required to perform tasks based on the instruction.If repeating the same task as the previous trial,we call the current trial “task repetition”,or else we call it “task switching”.It is constantly found that switching between tasks is slower and more error-prone than repeating the same task,and the difference between them is deemed as “switch cost”.Task dominance is defined as the level of automatic processing,usually distinguished by the asymmetric interference between tasks.A large number of studies showed that switch cost is modulated by task dominance,that is,switch cost is larger for dominant task than for nondominant task.The phenomenon is known as asymmetric switch cost.Allport et al.(1994)put forward a theory of task-set inertia,which attributed asymmetric switch cost to the persistence of task-set inhibition of previous trial.However,Some studies found the reversal of asymmetric switch cost by manipulating variables,such as changing the task types,reducing the interference between tasks and so on.So there are still many controversies on the mechanisms underlying asymmetric switch cost,the focus of which is that whether it is mainly caused by negative priming as a form of persistence of previous task-set inhibition,whether it is involved with other cognitive control processes? Owing to n-2 task repetition cost as a direct evidence of inhibition process in task switching,the present study divided “task switching(e.g.task sequence AB)” into “alternating switching(the task type of trial n-2 is the same as that of trial n,BAB)” and “single switching(the task type of trial n-2 is different from that of trial n,AAB)”.Alternating switching is a process of performing a recently inhibited task-set(overcome the nagetive priming of previous trial),representing the inhibition process of task switching.In contrast,single switching involves the generation of a new,non-inhibited task-set(reconfiguration process).The present study attempted to separate the inhibition process from reconfiguration process to consider the contribution of them individually in asymmetric task switching.What's more,we make full use of the high spatial resolution of functional magnetic resonance imaging(f MRI)technology to deeply explore the cognitive and neural mechanisms of task dominance affecting task switching.The present study consists of three parts:Experiment 1 was to verify whether the color naming task and the word reading task of variant stroop stimulus are a pair of tasks of unequal dominance.According to the definition of task dominance,we tested whether these tasks showed asymmetric interference by analyzing the interaction effect between task type(color naming task,word reading task)and trial type(congruent,incongruent).The results showed both tasks existed congruent effect and the congruent effect of color naming task was larger than that of word reading task.So we could regard color naming task of the stroop stimulus as non-dominant task,and word reading task as dominant task.Based on Experiment 1,Experiment 2 combined color-word stroop stimulus and taskcuing switching paradigm to investigate the effect of task dominance on switch cost.Importantly,by dividing “task switching” into two parts,we investigate the role of inhibition and reconfiguration in asymmetric task switching.Behavioral results found that switch cost of word naming task was greater than that of color naming task as a whole.By further analyzing the components of switch cost,it was reported that single switch cost of color naming task was greater than that of word reading task,while alternating switch cost of word reading task was larger than that of color naming task..Experiment 3 confirmed the behavioral results in Experiment 2,and the brain imaging results suggested that lateral prefrontal cortex(LPFC),anterior cingulate cortex(ACC)and inferior temporal gyrus(ITG)were significantly activated by the inhibition control during task switching when compared with task repetition.However,there was no remarkably activation by endogenous control of rebuild a new task-set,which demonstrated cognitive control network(bilateral inferior frontal cortex: IFG,left inferior parietal cortex:IPL,bilateral middle temporal gyrus:MTG)associated with reconfiguration process maybe domain-specific,resulting in a breakdown when switching to a new task.Considering the switching effect of different task types,it was discovered that higher activity of putamen and lower activity of hippocampal gyrus were found for alternating switching process of word reading task,which suggested that alternating switch cost of word reading task may derive from the blocked process of retrieval of stimulus-response mapping from long term memory.In the meantime,the activities of putamen and insula were lower for single switch process of color naming task than that of word reading task,showing that it was more difficult for color naming task to activate the relevant cognitive control network associated with reconfiguration process.In sum,the present study combining behavioral and f MRI technology suggests the effect of task dominance on task switching is not only reflected in the inhibition process(the negative priming effect of the previous task set),but also in the non-inhibition process(rebuild a new task-set).It's inhibition control and endogenous control during task switching modulated by task dominance that contribute to the emergence of asymmetric switch cost.