Time gain influences adaptive visual-motor isometric force control

This study examined the influence of time gain on the visual-motor control of isometric force. Time gain denotes the spatial length on the computer screen representing the unit of elapsed time of the force output, through which the time properties of the visually perceived force output can be compressed or extended. Five time gains and three force target waveforms (sinewave, brown noise, and straight line) with different time-dependent properties were tested in the experiment. The results revealed that time gain influenced task performance nonlinearly in a way that was dependent on the predictability of the target waveforms. In the sinewave target condition, there was a U-shaped modulation of time gain on the mean and variability of force error, and an inverted U-shaped modulation on the time-dependent structure of force variability. The time gain modulation effect was weaker in the brown noise target condition and absent in the constant force target condition. The results extend the effect of visual information gain regulation from force gain to time gain. The interaction between the time gain and target waveform supports the general proposition that the control of motor output is influenced by the interaction of different categories of constraints where the influence of visual information is dependent on the temporal properties and predictability of the force output and the task requirement.