Human sensitivity to expanding and rotating motion: effects of complementary masking and directional structure.

A comparison of sensitivity to expanding, rotating, translating and random motion suggests the existence of specialised mechanism for the detection of expansion and rotation. Complementary masking shows that the detection of expansion is unaffected by the presence of rotation, and vice versa. These results are interpreted in terms of a Relative Motion System, which combines the outputs of localised motion detectors in a variety of ways, and which functions to analyse complex image motion into simpler, more useful, components.