The Process Mechanism Of Cue-removed Task-switching Paradigm

Task switching is one of the important paradigms used extensively to study cognitive flexibility. Operators are required to monitor multiple information sources and switch between different activated under time pressures. So switching flexibility from different tasks is demanded in the design of human-machine interfaces. Since Jersild adopted task-switching paradigm, this paradigm has many revised version and has been extensively used to study task switching. There are at least two types of paradigm:predictable task-switching paradigm and unpredictable task-switching paradigm. The common way of providing advanced information predictable task-switching paradigm is using a fixed and easily predictable task-sequence which is provided cue or not. So this paradigm is called fixed sequence paradigm as well. It is generally provided a cue before you perform a task in predictable task switching paradigm, and its so called task-cueing paradigm or cued task-switching paradigm.Previous studies are focused on investigate the source of the switch costs in task switching. Some researchers construct their theory in terms of only one mechanism to explain switch costs. Although there still researchers proposed many single facto model in studying switching tasks, more and more researchers suggested that there should be existed multiple mechanism in task switching. Dispute has not been stopped on the actual factors that modified the switch costs. We adopted delta plots to analyze the conflict control mechanism dynamically in processing switch task in order that we can explore the dynamic change and understand the essential of the switch costs deeply. Actually, there are multiple paradigms of task switching when adopted neuro-psychology method to investigate switching task. Different task-switching paradigms are variable in process per se. we should study one of the paradigm concretely and deeply in order to comprehensively understand concrete processing of task-switching paradigm.Applying letter and number as experimental materials of task-switching study, we studied the neural mechanism of cue-removed task-switching paradigm in cross-sectional study and developmental study. Firstly, adopting delta plot methodology we compare three task-switching paradigm-fixed sequence task-switching paradigm, cued task-switching paradigm and cue-removed task-switching paradigm. Based the data followed we draw a conclusion that switch costs are variable dynamically and not inevitable result in processing switch task. Then we deeply explored the time characteristics of event-related potential in cue-removed task-switching paradigm and studied sequence order effects and conflict control effects of this paradigm. Furthermore we investigate the cue effect by comparing the short cue and long cue and compareing consistent cue and conflict cue for the sake of understanding the cue presenting mode on processing switch task.The main results are described in the following:(1) By analyzing the source of the switch cost with delta plot, we conclude that switch costs are not inevitable product in processing switch task. It is involve in the dynamical change mechanism when processed switch task. It depends on the balance between the degree of response inhibition of the last trial and the degree of activation the current trial. So we can explain why different task-switching paradigm product different switch cost, and we can also explain why there is different switch cost adopting the same switching task when the preparing time is different.(2) Applying ERP technique, we analyze the cue-locked time window and stimulus-locked time window individually. The different process mechanism and different effect in these two phases are put forward. There are task main effects between repeat task and switch task when analyzing the cue-locked time window. This because more sources are demanded when one performs the repeat task since you should control the response inhibition. Repeat task evoked larger P3b potentials than switch task at 500-700ms. Switch task are noticed later than repeat task in early attention phases. Its process needs more attention resources than repeat task as well. The ERP components reflect the switch effects is larger P2 amplitude in switch task than repeat task. The latency of P2 in switch task is longer than repeat task. It suggested that subjects put more resources into switch task in early attention time, so they modulate their attention slowly. There are task main effects after stimulus onset. Its due to the different interfere to number task and letter task. It's well known that we are familiar with number tasks when compare with letter tasks. When letter stimulus is the irrelevant stimulus, there are more disturbs when perform number task than perform letter task since letter task would interfere with number task. So the main task effects attained. Letter task elicit larger late positive components (LPC) at 700-1000ms time phase.(3)There are differences between short cue and long cue in cue-removed task-switching process. The cue effects and task effects are dissociate at cue-locked time window. The ERP components reflects the task effects is a larger P3b amplitude in repeat task than switch task in 300-550ms cue-locked window, and the components reflects the cue effects is a larger LPC in short cue than long cue. The result of dipole source indicates that the encephalic source is Cingulate Cortex and right frontal lobe for the former effects, and the right frontal lobe and BA19 of right occipital lobe for the latter effects individually.The early components at stimulus-locked window are attained that a longer latency of N1 component and larger amplitude of P2 component. This may suggested that one notice the long cue slower than that of short cue, but the long cue stimulus evoke more conflict that that of short cue. Also in early components of P2, the latency of short cue is shorter than that of long cue, but the amplitude of short cue is larger that of long cue.it may reflect that the different anticipated preparation of different cue.(4) Whether the cue is consistent with the task or not may affect the process of cue-removed task-switching. A longer latency of P2 components is got in switch task than in repeat task at front and middle electrode. The ERP component reflects the task effects is larger P3b amplitude in repeat task than switch task in 400-800ms cue-locked window. Repeat task elicit a larger LPC than switch task in 800-1000 ms time window. At the posterior electrode, conflict cue evoked a more positive trend component than consistent cue. This may suggest that subjects make more preparation when the cue is not consistent with the task.The early components effects are significant at stimulus-locked window. Larger P2 amplitude is elicited in repeat than in switch task. The consistent cue evokes a longer latency of P2 and N2 components than the conflict cue. It may imply that subjects devoted more early attention to the stimulus process in switch task than in repeat task, however when they process a conflict cue task, they may notice the conflict information and identify the stimulus quickly. (5) The result of the sequence effects of cue-removed task-switching is put forward as follows. There are significant first order effects but not second order effects both in cue-locked time window and stimulus-locked window. In other words, there are significant effects to process switch task when the current trail is not the same task as the last trail. But it's nothing important when the last trial is not the same task as the trial before it. Though behavioral study showed that there is both first order effects and second effects in reactive time of processing switch task. We should be cautious to explain the result since we haven't got the same result from the ERP and fMRI study. The different result may come from the methodology of behavior and ERP,fMRI, it may come from the experimental design per se. Since former method is focus on the variety of the process, the latter focus on the difference components on different reactive time phase.(6) The conflict control mechanism research of cue-removed task-switching showed that there is significant conflict effects in processing the task not only in cue-locked time window but also in stimulus-locked time window. No significant control effects exist in the cue-removed task-switching. This may suggest that the last task would affect the process of the current task when the last task is colliding with the current task. That is significant effects when perform current conflict task which is not the same as the last task. But the control level is not affect the current process whatever the control level is.There are important theoretical meaning and practical meaning of this research. Theoretically, we can comprehensively understand the switch cost of task switching. It can enrich the relative theory of process the switching task. Furthermore, we apply the methodology of delta plot to research the conflict control mechanism in switching task. This method analyzes the processing of task switching dynamically. It has more ecological validity than just analyzing by one single theory. Practically, the nature of cue-removed task-switching paradigm is valuable to further study the cognitive flexibility of human being. It can support an important design thought especially for construct human-machine interface and traffic signal system.