We recently found orientation constancy with respect to direction of gravity in the alert monkey. This seems to rely on a polysensory interaction that involves different sense-specific reference frames. Thus, we will challenge the assumption that the sense-specific reference frames are mutually exclusive. At the same time, we will highlight the dynamic tuning of the receptors that might rely on cross-modal mechanisms.

In line with my model of object motion perception (Wertheim 1994) and in contradistinction to what Stoffregen (1994) states, Sauvan's data suggest that percepts of motion are not sense specific. It is here argued that percepts of object- or self-motion are neither sense specific nor do they necessarily stem from what Stoffregen calls “kinematic events.” Stoffregen's error is in believing that we can only perceive object- or self-motion relative to other objects, which implies a failure to realise that percepts of absolute object- or self-motion in space (relative to the earth's surface) do exist as well, even when the earth's surface itself is not perceived.