EC is used to predict changes in sensory signals from proprioceptors expected from the planned action (ReA, reafference) this process involves conversion of EC into “EC” expressed in units commensurate with those encoded by afferent signals. Exafference always affected perception of relevant variables, whereas reafference affected perception only if it differed from the prediction based on EC.įigure 1.The classical scheme of the efference copy (EC) as a copy of the output of the alpha-motoneuronal pool. They always led to reflex-based corrections. If movement was produced by an external force acting on the effector, changes in proprioceptors were addressed as exafference. If, however, the prediction happened to be wrong, an error signal was sent to the alpha-motoneurons leading to correction of the action. If the prediction was accurate, no correction was issued. 1 emphasize that these signals are somehow transformed into units that make them comparable with signals from proprioceptors. In their scheme, a copy of the signals from alpha-motoneurons was used to predict changes in sensory signals from proprioceptors expected from the planned action (so-called, reafference). 1), which were assumed to participate in both perception and correction of the ongoing action in cases of movement errors.
In their original paper, von Holst and Mittelstaedt associated EC with a copy of the signals from alpha-motoneuronal pools ( Fig. To search for an answer to this question, “efferent process” and “perception” have to be defined explicitly. Despite literally hundreds of papers addressing and exploring these notions, the question posed in the title of this review remains without a clear answer. An important step was made in the middle of the XX-th century by von Holst and Mittelstaedt ( 4) and by Sperry ( 5) who introduced the notion of a copy of the ongoing efferent process used for perception: efference copy (EC), or efferent copy, or corollary discharge. In contrast, if eye position is displaced in an unusual way, e.g., by pressing on the eyeball with a finger, one has an illusory percept that the environment moves. He noticed that natural motion of an eye (assume that the other eye is closed) leads to veridical perception of eye motion in the motionless environment. Arguably, the first scientist who paid attention to effects of action on perception was von Helmholtz. It has been well established that perception of various modalities depends on the ongoing action-related, efferent process (reviewed in 1– 3). INTRODUCTION: THE CLASSICAL NOTION OF “EFFERENCE COPY” Distortions in efference copy happen spontaneously and can also be caused by changes in sensory signals, e.g., those produced by muscle vibration. Sense of effort is associated with such distorted efferent signals. Taken together, these results suggest that participation of efferent signals in perception frequently involves distorted copies of actual neural commands, particularly those to antagonist muscles.
These include, in particular, lower accuracy in perception of variables produced by elements involved in a multielement task compared with the same elements in single-element tasks, dissociation between motor and perceptual effects of muscle coactivation, force illusions induced by muscle vibration, and errors in perception of unintentional drifts in performance. This theoretical scheme has led recently to a number of novel predictions and findings.
Abundance of efferent and afferent signals is viewed as the means of stabilizing both salient action characteristics and salient percepts formalized as stable manifolds in high-dimensional spaces of relevant elemental variables.
The apparent redundancy in both motor and perceptual processes is reconsidered based on the principle of abundance. In this review, we consider definitions for efference copy, percept, and sense of effort based on recent studies within the physical approach, which assumes that the neural control of movement is based on principles of parametric control and involves defining time-varying profiles of spatial referent coordinates for the effectors. A number of notions in the fields of motor control and kinesthetic perception have been used without clear definitions.
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