Neural correlates of the stereokinetic effect revealed by functional magnetic resonance imaging.

The stereokinetic effect (SKE) refers to a visual phenomenon in which a two-dimensional figure rotating in the fronto-parallel plane about the visual axis can create the impression of a three-dimensional (3-D) object. Although several characteristics of SKE suggest that the perceptual mechanisms involved in SKE may differ from those of the kinetic depth effect (KDE), the differences between SKE and KDE in neural mechanisms have not yet been investigated. In order to determine the cortical areas involved in SKE, we presented a variety of SKE stimuli in a series of functional magnetic resonance imaging experiments, controlling for motion and contrast energies as well as stimulus presentation paradigm. Cortical activation associated with SKE was observed in the middle temporal complex (hMT+), lateral occipital area (LO), V3B, inferior temporal gyrus (ITG), fusiform gyrus (FG), and dorsal intraparietal sulcus anterior (DIPSA). On the other hand, ITG, FG, and DIPSA were also activated by the static versions of SKE stimuli. hMT+, LO, and V3B are also known to be activated in KDE. These findings suggest that general motion-dependent 3-D object processing may be performed in these areas.