Signals of eye-muscle proprioception modulate perceived motion smear

Achieving clear perception during eye movements is one of the major challenges that the human visual system has to face every day. Like most light sensitive mechanisms, the human visual system has a finite integration time that may cause moving images to appear smeared. By comparing the perceived motion smear during ongoing eye movements and fixation, previous studies indicated that smear is reduced by a neural compensation mechanism that uses "extra-retinal information" about eye movements. However, it is not clear whether eye-muscle proprioception (afferent input), internal copies of efferent oculomotor commands (efference copy), or both contribute to the smear reduction. The present study found that similar reductions of perceived motion smear occur during passive eye movement (which is signaled only by eye-muscle proprioception) and during active pursuit tracking (for which efference copy signals exist as well). These results reveal a novel neural contribution for maintaining visual clarity and stand in contrast to previous reports that eye-muscle proprioception makes only a minor contribution to visual perception.