Cognitive Neural Mechanism Of Training Effect On Inhibition Of Return

Inhibition of return(IOR) refers to slower responses to targets presented at the previously cued location than to those at uncued locations when the cue-target onset asynchrony is more than about 250 ms. Although lots of studies have shown about aspects of IOR, much has been debated about whether the training affects IOR.In the experiment One, we tried to explore the training effect on IOR in normal participants by using of a long-term training procedure. 21 participants were required to finish a task combined the cue-target paradigm and Stroop task in 8 successive days. Specifically, in each training day, the participants were asked to react as fast and accurate as possible to the displayed color of Stroop stimuli(color words) presented at either the cued or uncued locations. Results showed that the IOR effect decreased significantly as the training days increased in both the traditional RTs difference index or the RTs ration index. The finding suggests that there is a stable training effect on IOR.However, how the training shapes IOR is still an opening question. The experiment Two based on the experiment One is aimed to tackle this question by using the Event-Related Potentials that are superior in time-resolution and hence are sensitivity in tracking the distinct information processing stages. 24 participants were asked to discriminate target stimuli(“@”or “&”) presented at either the previously cued or uncued locations in 9 successive days. During the first and the last training day, the electroencephalogram(EEG) data were acquired while the participants performed the task. Results showed that: 1) Behaviorally, consistent with the results of the experiment One, the IOR effect(RTcued – RTuncued) decreased steadily and significantly as the training days increased; 2) Electro-physiologically, compatible with previous ERPs studies of IOR, the target stimuli occurred at cued locations elicited smaller N1(170~200 ms) as well as the P2(240 ~ 280 ms) than that at uncued locations; 3) And more interestingly, while N1 cueing effect(N1uncued- N1cued) and P2 cueing effect(the Nd250) decreased significantly from the first to the last training day, the P1 cueing effect kept constant across the training days.Taken together, 1) IOR could be affected reliably by 8-days training, supporting the “lack of enough training” explanation for the previous inconsistent results about the practice effect of IOR. 2) as the visual N1 cueing effect has been well demonstrated to reflect the perceptual processing(e.g., discrimination process), the current results suggested that information stages related to perceptual processing play a key role in the effect of training on IOR, providing,as far as we known, the first electrophysiological evidence for the cognitive neural mechanism of the training effect of IOR. And 3) the significant regression of the behavioral IOR effect on the N1 and the P2 cueing effect(Nd250) instead of the P1 cueing effect suggested that the N1 and Nd250 may be the more robust and reliable electrophysiological indexes of IOR.