ABSTRACT
In recent physiological and related psychophysical studies, similarities have been found between the response properties of individual vestibular nuclei neurons and certain characteristics of visually induced apparent self-motion. These findings have led to the development of linear sensory-convergence models of body orientation. In the present chapter, we demonstrate that illusory self-rotation and compensatory nystagmus can be elicited in seated, stationary subjects (a) by somatosensory stimulation of the soles of the restrained feet, (b) by pedaling a motor-driven platform and (c) by pedaling a free-moving platform. These observations extend the range of afferent patterns that influence apparent orientation and indicate that efferent inputs are also involved. In fact, the motor figure-ground reversals produced the most intense illusions and compensatory nystagmuses. The pattern of our results is inconsistent with single-neuron sensory convergence models of orientation. Instead, our findings make it clear that the ongoing, perceived orientation of the body is determined on the basis of computations involving multiple sensory and motor patterns conveying information about the configuration of the entire body. One consequence of these computations is a lability in the representation of the apparent position of the parts of the body in relation to each other and of the body in relation to its environment.
