The visual system can construct representations of complex 3-D shapes using 2-D motion information, as this movie demonstrates. You may gain an impression of a rotating sphere in the middle of the display, but only when the pattern is moving (try pausing the movie). Depth is conveyed solely by the variation in velocity and direction of the dots. This effect is also known as 'structure-from-motion' or SFM. The movements of individual dots can be encoded by low- and mid-level motion processes, but the construction of 3-D shape from variations in 2-D motion requires sophisticated high-level processes operating over large areas of the display.
In which direction does the sphere appear to rotate? The perspective information (variation in dot path and velocity) defines anticlockwise rotation (viewed from above), but the display may appear ambiguous.
See:
Wallach, H. & O'Connell, D.N. (1953) The kinetic depth effect. Journal of Experimental Psychology, 45, 205-217.
Mather, G. (1989) Early motion processes and the Kinetic Depth Effect. Quarterly Journal of Experimental Psychology, 41, 183-198.
Peuskens, H., Claeys, K. G., Todd, J. T., Norman, J. F., Van Hecke, P., & Orban, G. A. (2004). Attention to 3-D shape, 3-D motion, and texture in 3-D structure from motion displays. Journal of cognitive neuroscience, 16, 665-682.