Abstract
Space constancy, the appearance of a stable visual world despite shifts of all visual input with each eye movement, has been explained historically with a compensatory signal (efference copy or corollary discharge) that subtracts the eye movement signal from the retinal image shift accompanying each eye movement. Quantitative measures have shown the signal to be too small and too slow to mediate space constancy unaided. Newer theories discard the compensation idea, instead calibrating vision to each saccadic target.
Highlights
All visual information arrives in the brain through the retinal receptors that are in nearly continuous motion as the eyes flit from one fixation to another
How is the stabilization accomplished? This is the problem of space constancy
Until a few decades ago the dominant theory evoked a signal emanating from motor areas of the brain to inform the visual system about eye movements
Summary
Helmholtz (1866 [1962]) expanded the empirical base for efference copy with observations of neurological patients who had eye muscle damage He called the intention to change gaze position a ‘Willensanstrengung’, an effort of will. Another extraretinal signal, proprioception from the eye muscles, was later proposed as a source of information that could contribute to space constancy (Sherrington 1918). Sperry (1950) made similar observations in a fish with a surgically inverted eye, naming the signal corollary discharge. These papers formalized the compensation idea that had dominated for more than a century.
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