In humans, tendon vibration evokes illusory sensations of movement that are usually
associated with an excitatory tonic response in muscles antagonistic to those vibrated
(antagonist vibratory response, AVR), i.e., in the muscle groups normally contracted
if the illusory movement had been performed. The aim of the present study was to investigate
the relation between the parameters of the illusory sensation of movement and those
of the AVR and to determine whether vectorial models could account for the integration
of proprioceptive inputs from several muscles, as well as for the organization of
the elementary motor commands leading to one unified motor response. For that purpose,
we analyzed the relations between the anatomical site of the tendon vibration, the
direction of the illusory movement, the muscles in which the AVR develops, and the
characteristics of the AVR (surface EMG, motor unit types, firing rates, and activation
latencies). This study confirmed the close relationship between the parameters of
an AVR and those of the kinesthetic illusion. It showed that, during illusions of
movements in different directions, motor units are activated according to a specific
pattern correlated with their type, with the direction of the illusory movement and
with the biomechanical properties of their bearing muscles. Finally, kinesthetic illusions
and AVRs can be effectively represented using similar vectorial computations. These
strong relations between the perceptual and motor effects of tendon vibration once
again suggest that the AVR may result from a perceptual-to-motor transformation of
proprioceptive information, rather than from spinal reflex mechanisms.