The Mechanisms Underlying The Modulation Of Fear Conditioning On Visual Size Illusion

Emotion and perception interact reciprocally in our daily life.Previous studies have found that fear conditioning can affect visual perceptual processing,whereas the underlying neural mechanisms are largely unexplored.Here we conducted a behavioral experiment(N= 20)and an fMRI experiment(N = 50)to probe the neural networks underlying the fear-related modulation effect on the well-known Ebbinghaus illusion.To establish fear conditioning,the surrounding large circles of the Ebbinghaus configuration were repeatedly coupled with a white noise(92 dB,1000 ms)for one half of participants,and the surrounding small circles were coupled with the white noise for the other half of participants.The Ebbinghaus illusion effect was measured immediately.Experiment 1focused on the effect of fear conditioning on the Ebbinghaus illusion at the behavioral level,and the results showed that compared to the nonfear-conditioned condition,the fear conditioned condition significantly increased both underestimation and overestimation aspects of the illusion,i.e.,the perceived illusion magnitude was significantly increased,suggesting that fear conditioning does have an effect on the Ebbinghaus illusion.We next used the fMRI technique to investigate the neural networks underlying the fear conditioning effect on the Ebbinghaus illusion.The results of the group level GLM showed significant activation of the left inferior occipital gyrus(IOG),the left superior parietal lobule(SPL)and the left thalamus(THA)in response to illusory configurations irrespective of emotional content.Subsequent ROI analysis showed that for the underestimation aspect of the illusion,the average IOG BOLD signal response to CS+ decreased significantly compared to CS-,while for the overestimation aspect,the IOG response to CS+ increased significantly than CS-.Although for the underestimation aspect,there was no significant difference between the average BOLD signal response to CS+ and CS-in the left SPL and the left THA,there was also a decreasing trend.For the overestimation aspect,the average BOLD signal response of CS+ was significantly higher than that of CS-.Finally,the DCM results showed that the modulatory effect of fear conditioning on the illusion was manifested as increased connections from SPL and THA to IOG and decreased inhibitory self-connection in IOG.Based on the above results,this study not only finds that fear conditioning can modulate visual size perception by regulating the connections between subcortical and cortical regions,but also provides evidence in favor of different mechanisms underlying the overestimation and underestimation aspects of visual size illusion.