The selected rest frame is hypothesized to underlie our perception of
position, angular orientation and motion, both for self and for external
objects. Crossing ``self'' or ``external object'' with ``position'',
``orientation'' or ``motion'', we would expect that visual background
manipulations which alter the selected rest frame should produce 6 types of
``illusions''![[*]](/host/stout4/perseant/latex2html/icons.gif/foot_motif.gif){kind=icon}
.
For 5 of these 6 cases (the sixth being ``self and position'') it is well-known that visual background manipulations can produce the indicated illusion. The six possibilities are itemized below.
Self and Motion. The visually-induced perception of self-motion is called ``vection''. For instance, if one is seated in a stationary car at a traffic light, and the adjacent car rolls backwards, one may have a sustained impression that one is moving forwards. Recent work implies that vection is heavily influenced by one's relative motion with respect to the perceived visual background. See Section 2.4.1.
External Objects and Motion. If one moves the background behind an object, one often has the impression that the object is moving in the opposite direction to the background. This is called ``induced motion'' [106].
Self and Orientation. If one is placed in a room in which the walls are tilted, one tends to perceive that one is tilted in the opposite direction [45].
External Objects and Orientation. A tilted background can alter one's perception of the orientation of an object in the foreground with respect to gravity [45].
Self and Position. It is suggested that presence, the sense of ``being somewhere'', encompasses this kind of illusion. See the discussion of the ``presence hypothesis'', below.
External Objects and Position. Visual background manipulations may alter the perceived distance to objects, which is a form of position illusion. For instance, in the ``corridor illusion'', linear perspective is used to alter the perceived depth (and therefore size) of an object [60].