Shared neural sensory signals for eye-hand coordination in humans

Abstract

Previous studies that examined eye and hand tracking using either a self-driven or a predictable moving target proposed that eye-hand coordination is realized by a coordination control system that uses both efferent and afferent information of hand movement to synchronize and couple eye and hand motor systems. In the current study, we examined the correlation between the noises of eye and hand tracking of an unpredictable moving target that made efferent and afferent information of hand movement unusable. In Experiment 1, two experimental conditions were tested: in the eye-hand condition, while participants used their eyes to track the movement of a Gaussian target (σ=0.6 deg) on a computer display (40 deg H x 30 deg V) as its horizontal position was perturbed by the sum of seven harmonically-unrelated sinusoids (0.1-2.19 Hz), they also used their dominant hand to control the horizontal position of a second vertically-offset Gaussian cursor (8 deg below) with a high-precision mouse to align it with the target. In the eye-alone condition, the target and cursor positions previously recorded in the eye-hand condition were played back, and participants were instructed to use only their eyes to track the movement of the target. In Experiment 2, the same two experimental conditions were tested except that there was no cursor to indicate hand tracking on the screen. Prior to computing the correlation between the noises of eye and hand tracking responses, for each 90-s trial, we subtracted best-fitting linear tracking responses at the seven input perturbation frequencies to remove direct correlation with the visual stimulus. For both experiments, trial-by-trial examination revealed that the correlation between the residual noises in eye and hand tracking in the eye-hand condition was both highly significant and much higher than the spurious correlation found when eye tracking was not accompanied by simultaneous hand tracking in the eye-alone condition. Our study provides the first behavioral evidence showing that common neural sensory signals drive both eye and hand motor systems and limit eye-hand coordination. This is consistent with the neurophysiological findings of common neural substrates that serve both eye and hand tracking.