Neural Correlates Of Serial Order Effect In Verbal Divergent Thinking

During the course of divergent thinking(DT),the number of the generated ideas decreases while the originality of ideas increases.This phenomenon is labeled as serial order effect in DT.In this study,EEG alpha power was used as biomarker to see the brain activity and neural correlates of the serial order effect in DT.The present study also investigated whether different executive functions(EF)(i.e.,updating,shifting,and inhibition)contribute to the serial order effect in DT separately.Participants9 executive functions were measured by corresponding experimental tasks outside the EEG lab.In Study 1,participants were required to generate original uses of conventional objects(alternative uses task,AUT)during EEG recording.The participants were asked to report the ideas orally as soon as they generate one idea.The behavioral results revealed that the originality of ideas was higher in later stage of DT(i.e.,Epoch 2)than in its earlier stage(i.e.,Epoch 1)for higher-shifting individuals,but showed no difference between two epochs for lower-shifting individuals.The EEG results revealed that lower-inhibition individuals showed stronger upper alpha(10-13 Hz)synchronization in left frontal areas during Epoch 1 compared to during Epoch 2.For higher-inhibition individuals,no changes in upper alpha activity from Epoch 1 to Epoch 2 were found.These findings indicated that shifting and inhibition contributed to create a serial order effect in DT,perhaps because individuals suppressed interference from obvious ideas and switch to new idea categories during DT,thus more original ideas appear as time passes by.In Study 2,participants were required to do the AU task as well as two fluency tasks,Phonetics Fluency(PF)task and Semantic Fluency(SF)task during EEG recording.The EF tasks were finished after them without EEG recording.The paradigm of the AU task was changed in Study 2,each AU word has four sessions.In each session,participants were asked to generate the ideas in 16 seconds and speak them aloud in another 10 seconds.The paradigm of the fluency tasks(PF and SF tasks)were the same as AU task.The behavioral results revealed that the fluency of ideas decreased in each Epoch in AU,PF and SF tasks and the originality of AU task was higher in Epoch 2 than in Epoch 1,but no difference between Epoch 3and Epoch 4.The EEG results revealed that upper alpha increased from Epoch 1 to Epoch 4 during AU task.Higher-Inhibition and higher-Updating individuals showed stronger upper alpha synchronization in posterior area(occipital lobe)than lower-inhibition and lower-updating individuals.These findings in Study 1 and 2 provided the strong evidences of serial order effect in divergent thinking task.Moreover,EEG alpha power increased gradually in frontal and posterior cortex during divergent thinking task,which may reflect the state of internal attention and top-down control.Executive functions also contributed to the serial order effect by means of shifting and inhibition.Individuals may shift their strategies such as switching idea categories and inhibit the uncommon ideas comes to their mind at the beginning to generate more original ideas,which may play an important role in serial order effect of divergent thinking.