The effects of dynamic visual stimulation on perception and motor control.

A set of research findings is described that deals with three principal laboratory measures of visual orientation (vection and postural and manual control). Two studies are highlighted, one of which compared the latencies of vection and visually induced postural change and the other of which investigated manual tracking under visually disorienting conditions. The first study showed that although vection and postural change are somewhat related to each other (for example, both were greater in response to roll and pitch as opposed to linear visual motion), the onset of vection is delayed by several seconds relative to the initiation of visually induced postural shifts. The second study showed that manual biases induced by visual roll motion are not overcome using a thumb-and-forefinger (pyramidal) motor strategy, and may not be equivalent to the "giant hand" illusion that is believed to reflect the predominance of the vestibulospinal (extrapyramidal) motor pathways during extreme spatial disorientation. These and other findings indicate that various visual orientation effects may involve at least partially independent mechanisms.