Abstract
We usually think of well-learned daily limb movements, such as reaching and walking, as being fully controlled by our action intentions. Typically, the sensory outcomes of our movements would be recognized as self-actions (as opposed to movements of the external world) due to an internal model prediction using ‘efference copy’ of our motor commands. Here we describe a series of exceptions to this rule, which can be observed in implicit motor processes. One is the ‘manual following response’ that is induced by visual motion applied during reaching movements of the arm. This implicit visuomotor response alters our perception of self-movement. Even though the manual following response is self-generated, subjects tend to perceive it as an externally generated movement. Another example is the clumsy body and leg movements that occur when we step onto a stationary escalator, and the associated odd sensation that subjects frequently report. Even though we completely understand the environmental state of the stopped escalator, we cannot avoid behaving clumsily, and feeling an odd sensation before adaptation. Experiments involving the systematic manipulation of visual information of an escalator and the surrounding visual motion further indicate that endogenous motor responses may be triggered by the expectation that the escalator is in fact moving. In addition, exogenous postural changes elicited by visual motion can induce a similarly odd sensation, suggesting that the implicit behavior itself is a key factor in the perception of movement.