The neural basis of impossible figures: evidence from an fMRI study of the two-pronged trident

In the present study, we used the two-pronged trident task to investigate the neural basis of impossible figures processing by using event-related functional magnetic resonance imaging (fMRI). Our fMRI results showed that there were no brain regions with significantly stronger responses to possible condition than to impossible condition. However, impossible condition showed significantly more activation in the right inferior temporal gyrus (ITG), the fusiform gyrus (FG) and the right superior parietal gyrus (SPG). The right SPG in the dorsal visual pathway might be related to spatial information processing and the right lateral occipital complex (LOC) (FG and ITG) in the ventral visual pathway (the object-selective regions) might be related to the representation of the impossible 3D structure. Therefore, our results indicated that the impossible 3D structure might be difficult to be represented by human visual system, and the impossible perception might be derived from the detecting and resolving the contradiction in the subjects' interpretations according to different perceptions triggered by 3D cues.