"Wiggle wiggle, little finger": The impact of eye movements on manual motor overflow during the imagination of a Fitts' aiming task

When individuals execute a reciprocal aiming task, eye movements tend to precede the hand movements to enhance error correction and accuracy. This coupling also occurs when imagining the motor task. In fact, the eye movements still emerge even when the hand remains relatively still during the imagination of the manual aiming movements. The eye movements may be an expression of motor overflow that arises during the imagination process. Recent work in our lab suggests that suppressing eye movements decreases imagination accuracy. The activation of the internal representation and motor overflow during imagination can also be measured through small accompanying involuntary movements of the finger. The purpose of this study was to understand how the suppression of eye movements affects the manual motor overflow that emerges during the imagination of a Fitts' reciprocal aiming task. Participants first imagined, then executed the task in two conditions: 1) no instructions on eye movement (no-fixation); and, 2) instructions to fixate their eyes on a central target (fixation). During imagination, participants indicated the start and end of imagination by lifting their finger, holding it up, and bringing it back down once they were finished imagining the task. The manual motor overflow was measured as the movement of the participant's finger while it was held in the air. Although Fitts' law still emerged within conditions, the manual motor overflow was similar across the fixation and no fixation conditions. Thus, manual motor overflow does not seem to be influenced by eye movements during action imagination.