Neural Correlates of Perceiving Visual Scenes as “Natural” or “Unnatural” - An fMRI Study with Contrast Modulated Pictures

Using functional magnetic resonance imaging, we examined whether distinct activity patterns are elicited by natural and unnatural visual stimuli. Stimuli were black and white pictures portraying various scenes (e.g., cities, country fields); natural pictures were unaltered, while unnatural pictures were produced by reversing their contrast curves (negative images). Low-contrast pictures were used in tandem to find contrast-sensitive areas in the contrast curves. During scanning, participants performed a simple discrimination task; brain imaging results revealed distinct activity patterns depending on stimulus type. When subjects viewed natural pictures, activity was greater in the angular gyrus and precuneus. In contrast, when viewing unnatural pictures, activity was greater in the fusiform gyrus, inferior temporal cortex, middle occipital cortex, and inferior frontal operculum. These findings indicate that the experience of perceiving visual stimuli as natural or unnatural might be subserved by cortical networks other than those known to be involved in the low-level processing of visual information.