The Neural Basis Of Poggendorff Illusion

Event-related brain potentials (ERPs) and functional Magnetic Resonance Imaging (fMRI) were used to examine the neural basis of the Poggendorff visual illusion effect. Our ERP data showed that suppressed amplitude of P1 was observed under Illusion Condition (experiencing illusion) relative to Baseline Condition and Illusion Condition elicited a more negative N350-450 than Baseline Condition. Combining our fMRI results, we thought that the cortex source of P1 for illusion might be the MOG (BA 18), which might reflect that the processing of the target (two oblique lines) were influenced by the context (two vertical parallel lines) in the early stage of the Poggendorff illusion; the cortex source of N350-450 might be right SOG (BA 19) and MOG (BA 19), which might reflect that the object perception was involved in the Poggendorff illusion generation. In addition, the discrepancy between Illusion Condition and No-illusion Conditions (experiencing no illusion) was observed only in the time window between 450 ms to 550 ms. Illusion Condition elicited a more negative N450-550 (LNC1) than No-illusion Condition on the infoposterior scalp regions. The fMRI results that the V1 (BA 17), V2 (BA18) and right Sperior Parietal gyrus (SPG) (BA 40) was significantly more activated in the Illusion Condition than in the No-illusion Condition. Combining the ERP and fMRI results that Illusion Condition minus No-illusion Condition, we thought the LNC1 in present study might be related to the VI (BA 17), V2 (BA18) and SPG (BA 40), which might reflect that the Poggenforff illusion effect was caused by the misperception of the angles, misapplied 3-D cues and spatial filtering as well as the interaction of these factors in the post-perceptual processing. Comparing Illusion Condition, however, the No-illusion elicited a more negative N450-550 (LNC2) on the anterior scalp regions. Moreover, the high-level visual cortexes [bilateral fusiform gyrus (FG) (BA 20) and left middle temporal pole (MTP)], the left medial superior frontal gyrus (MFG) (BA 32), right/left anterior cingulate cortex (ACC) (BA 24, BA 32), right superior frontal gyrus (STG) (BA 31), left medle frontal Gyrus (BA 8) were significantly more activated the No-Illusion Condition. Therefore, we thought that the LNC2 might be related to activated FG (BA 20), bilateral ACC and right mFG, which might reflect that no-illusion effect was the consequence that the low level visual cortexes were modulated by feedback information from the high level visual cortexes; the bilateral ACC and right mFG were involved in the interaction processes between low level and high level visual cortexes.