Neurolysyehologia, Vol. 17, pp. 241 to 2.58. Pergamon Press Ltd. 1979. Printed in Great Britain. COROLLARY DISCHARGE: ITS POSSIBLE IMPLICATIONS IN VISUAL AND OCULOMOTOR INTERACTIONS MARC JEANNEROD, HENRY KENNEDY and MICHEL MAGNIN Laboratoire de Neuropsychologie Exp~rimentale, INSERM U 94, 16, avenue Doyen L6pine, 69500 Bron, France Abstract--Data concerning the possible role of a corollary discharge mechanism in the regulation of visual-oculomotor interactions are reviewed. Several modes of action for such a mechanism on the processing of visual information are discussed. Mere suppression of visual input during saccades is considered mostly as a peripheral mechanism. It is proposed that corollary discharge could either produce an active cancellation of the effects of eye movements on vision, or contribute to the evaluation that a given visual change is provoked by a saccade. Cancellation could occur at subcortical levels of visual processing although evaluation could occur at the cortical level. INTRODUCTION THE QUESTION of how we feel our own actions is not a simple question. Besides inflow informations arising from peripheral receptors (visual, proprioceptive) and providing sen- sory cues as to the execution of a movement, another possibility has been postulated. At the beginning of the last century, the French philosopher Maine de Biran stated that actions must be revealed to the subject otherwise than by their effects, and that he must know them as such. Maine de Biran intuited that, without being caused by the will, muscular sensation (one of the effects of a movement) would only give us a purely passive feeling, as do heart beats or convulsive movements "that we feel without producing them purposively". Later, Helmholtz contributed to this notion by making the distinction, within what he called the muscular feeling, between two different sensations: the intensity of the effort of will, and the tension of the muscles. The concept that efforts of will, which lead to the execution of a movement, have central neural (and recordable) correlates has been particularly emphasized by H. L. Teuber. By using the term corollary discharge (first coined by Sperry), Teuber assumed that "each voluntary movement or change of posture, involves not only the downward discharge to the peripheral effectors, but a simultaneous central discharge from motor to sensory systems preparing the latter to those changes that will occur as a result of the intended movement" [1, p. 198]. Teuber was in fact quite in the same line of thinking as Maine de Biran when he claimed that "presence or absence of corollary discharge.., would determine whether a movement is voluntary or involuntary", and that "corollary discharge would serve as a physiological criterion for self-produced movements in contradistinction to reflexes" ([1] pp. 198-199; see also [2-4]). In his further descriptions, the terms voluntary and involuntary were often taken as equivalent for active and passive, respectively. This nuance may have more than a speculative interest. In the literature, the merging of the concept of corollary discharge has been closely related to the problem of visual 'stability' during movements of the eyes. Helmholtz inter- 241