Time-dependent effects of kinesthetic input

Sensory input can be used by the nervous system to control the spatial parameters of motor responses (e.g., distance, velocity, and direction) by initializing these parameters before movement onset and then by adjusting these parameters during movement. Sensory input can also be used to trigger movements. In the experiments reported in this paper, we compared the effects of kinesthetic input on a triggered motor response when the kinesthetic input was generated at different times relative to the onset of the motor response. Human subjects responded to a visual stimulus by intentionally increasing elbow torque to a target level. Kinesthetic input was generated by unexpectedly rotating each subject's elbow 100 ms before the onset of the intentional torque response (early) or coincident with the onset of the intentional torque response (late). The effect of early kinesthetic input on the intentional torque response markedly differed from the effect of late kinesthetic input. The effect of early kinesthetic input was relatively independent of the direction of elbow rotation, had a different dependence on the amplitude of rotation, and required a shorter duration of rotation compared to the effect of late kinesthetic input. These differences in the effects of early and late kinesthetic input might be related to the initialization, triggering, and adjustment of motor responses.