During self-generated movement it is postulated that an efference copy of the descending motor command, in conjunction with an internal model of both the motor system and environment, enables us to predict the consequences of our own actions (von Helmholtz, 1867; Sperry, 1950; von Holst, 1954; Wolpert, 1997). Such a prediction is evident in the precise anticipatory modulation of grip force seen when one hand pushes on an object gripped in the other hand (Johansson and Westling, 1984; Flanagan and Wing, 1993). Here we show that self-generation is not in itself sufficient for such a prediction. We used two robots to simulate virtual objects held in one hand and acted on by the other. Precise predictive grip force modulation of the restraining hand was highly dependent on the sensory feedback to the hand producing the load. The results show that predictive modulation requires not only that the movement is self-generated, but also that the efference copy and sensory feedback are consistent with a specific context; in this case, the manipulation of a single object. We propose a novel computational mechanism whereby the CNS uses multiple internal models, each corresponding to a different sensorimotor context, to estimate the probability that the motor system is acting within each context. Key words: internal model; forward models; prediction; grip force; virtual reality; bimanual coordination The ability to predict the consequences of our own actions using an internal model of both the motor system and the external world has emerged as an important theoretical concept in motor

Induced movement, illusory movement in a stationary stimulus resulting from adjoining movement, has received steady experimental investigation over the last 70 years or so. It is observed under different viewing conditions in a wide variety of displays that differ considerably in overall size and in form of inducing and induced stimuli. Explanations have been diverse, some being based on relations within the display and others invoking mediation by other aspects of the observer's perception. Probably, no one explanation can account for all forms of induced movement. Current knowledge about induced movement may have important implications for visual perception of object morion. Induced movement is one of a number of phenomena—including apparent movement, autokinetic movement, and movement aftereffect—in which movement is perceived, although the corresponding distal stimulus is physically stationary. It normally results from physical movement adjoining the stationary stimulus; the induced movement is in the direction opposite that of the adjoining movement. In a typical laboratory demonstration

Perceived stability of the visual world during eye movements is traditionally explained as due to the presence of extraretinal signals, equal in magnitude to retinal signals. Motion is perceived when the two signals differ. An experiment is reported in which motion thresholds were measured during smooth pursuit eye movements. The results show that the traditional view is incomplete. Motion is only perceived when the two signals differ by at least a just nottceahle dfference (JND), the magnitude of which depends on ocular velocity and is independent of the direction of stimulus motion relative to the eyes, The data lead to the rejection of theories according to which ocular velocity is under-represented in extraretinal signals. In addition they show that retinal image motion carries no information about stimulus motion. Perceived motion, direction and velocity are relative concepts. They depend on the JND and therefore they are relative to extraretinal signals. This principle explains the Filehne illusion and even predicts the Aubert-Fleischl phenomenon. A similar analysis can be applied to understand vestibular effects on motion perception.