Visual object cognition precedes but also temporally overlaps mental rotation.

Two-dimensional, mental rotation of alphanumeric characters and geometric figures is related to linear increases in parietal negativity between 400 and 800 ms as rotation increases, similar to linear increases with rotation in response times. This suggests that the frontoparietal networks implicated in mental rotation are engaged after 400 ms. However, the time course of three-dimensional object mental rotation using the classic Shepard-Metzler task has not been studied, even though this is one of the most commonly used versions in behavioral and neuroimaging work. Using this task, this study replicated a prior neuroimaging version using event-related potentials. Results confirmed linear mental rotation effects on performance and parietal negativity. In addition, a frontocentral N350 complex that indexes visual object cognition processes was more negative with mental rotation and showed linear trends at frontopolar sites from 200 to 700 ms and centrofrontal sites from 400 to 500 ms. The centrofrontal negativity has been implicated in object working memory processes in ventrolateral prefrontal and occipitotemporal areas. The frontopolar N350 has been implicated in processes that compute the spatial relations among parts of objects to resolve visual differences between object representations and enable an accurate cognitive decision involving a network of ventrocaudal intraparietal, ventral premotor, and inferotemporal cortices. Overall, the time course indicates that visual object cognition processes precede (200-500 ms) but also overlap the initial phase of mental rotation (500-700 ms) indexed by parietal negativity.