Applied Vision Association Easter Meeting Liverpool Hope University, Liverpool, UK 29 March 2010

摘要

All visual information arrives in the brain through the retinas, whose images are displaced with each eye movement, yet we perceive a stable visual world. How does the brain accomplish the stabilisation? Information about eye position comes from efference copy (a copy of the innerva- tion to the muscles that move the eye) and from proprioception (in those muscles). Together these extraretinal signals indicate the position of the eye. By pressing on the eyelid of a viewing eye, the extraocular muscles can be activated to maintain a steady gaze position without rotation of the eye. This procedure decouples efference copy from gaze position, making it possible to mea- sure the gain of the extraretinal signals. The gain is less than 1, leading to the conclusion that humans underestimate the deviations of their own eyes and that extraretinal signals cannot be the mechanisms underlying the perception that the world remains stable despite eye movements. The under-registration of eye deviation accounts quantitatively for a previously unexplained illusion of visual direction. Extraretinal signals are used in static conditions, especially for controlling motor behaviour. The role of extraretinal signals during a saccade, if any, is not to compensate the previous retinal position but to destroy it. Then perception can begin with a clean slate during the next fixation interval. Newer theories account for space constancy with current information only, not compensating for the effects of eye movements.