historically the problem of visual stability has been simplified to address only a fixed visual world with a fixed head . 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 . at the time of an eye movement
this signal would be subtracted from the resulting retinal image shift , achieving space constancy . because the idea requires that visual centers receive a copy of the neural efference to the eye muscles , von holst and mittelstaedt ( 1950 ) named it efference copy .
formal descriptions originated with bell ( 1823 ) and purkinje ( 1825 ) , who described it independently .
helmholtz ( 1866 ) expanded the empirical base for efference copy with observations of neurological patients who had eye muscle damage .
another extraretinal signal , proprioception from the eye muscles , was later proposed as a source of information that could contribute to space constancy ( sherrington 1918 ) .
not all theorists have accepted this position ; j j gibson asserted that motion of the entire visual field would always result in a perception of self - motion . asking
whether the world should appear to move when the visual field sweeps by , he answered ,  why should it move ?
the retina is proprioceptive  ( gibson 1966 p 256 ) . simply pressing on one eye
while closing the other disproves this assertion , for then the whole world appears to move .
von holst and mittelstaedt ( 1950 ) inverted the head of the blowfly eristalis , holding it with a piece of wax .
the fly would circle either clockwise or counterclockwise at random . in darkness , though , the fly 's locomotion seemed normal .
the conclusion was that the fly compared the output of its locomotor system with the retinal flow field ( since the fly 's eye is fixed to its head , and in the experiment is also fixed to the body , the locomotor system is also the oculomotor system ) .
the  efferenzkopie would subtract from the retinal signal to stabilize locomotion ( figure 1 ) . inverting the head converted the negative feedback to positive feedback
correct in the same direction , resulting in a further deviation in the same direction .
independently , sperry ( 1950 ) made similar observations in a fish with a surgically inverted eye , naming the signal corollary discharge .
use of efference copy to stabilize a perceived visual world , redrawn to american engineering conventions .
efference copy is subtracted (  ) from the visual input , afference ( + ) , at a comparator to present a stable representation to the brain .
first , efference copy informs the brain of where the eyes should be rather than where they are . as such it can not be exact  it should drift with time , and inaccuracies can not be corrected .
yet perceptual space constancy is perfect  the world does not appear to jump in the slightest when the eyes move .
further , quantitative measures of saccadic suppression of displacement showed that , at the optimal timing of image displacement and saccade , the perceptual threshold was nearly 1/3 as large as the saccade ( bridgeman et al 1975 ) . any orientation mechanism with an error this large
had no idea where the world was , and could support neither space constancy nor visual - motor calibration .
experiments exploiting alternating eye movements , either from rapidly repeated eye presses ( ilg et al 1989 ) or from rapidly alternating saccadic eye movements
( nagle et al 1980 ; grsser et al 1987 ) , demonstrated that both motor and sensory compensation were effective at low temporal frequencies but failed at higher frequencies .
thus any efference - copy - based system fails at rates well within the temporal range of normal perception .
the eyepress has been misunderstood since purkinje 's 1825 assumption that it elicits a passive eye movement ; the real situation is exactly the reverse .
the reader can easily verify this  pick a fixation target , then close one eye while slowly pressing on the other through the lid
. you will be able to hold your gaze on your fixation target while the visual world , target and all , appears to move . thus the retina is not moving with respect to the visual world .
rather than revealing the effect of passive eye movement , the eyepress shows the effect of active compensation for oculomotor disturbance .
efference copy alone can drive motion perception ( bridgeman and stark 1991 ) . pressing on the viewing eye changes efference without changing gaze position , but pressing on the covered eye
the covered eye when pressed should rotate under the eyelid , because the press does not result in any corrective signal from visual error feedback .
the situation in pressing the viewing eye is now more complicated , because efference copy and proprioception work in opposite directions .
proprioception will come from the deviated , covered eye , and altered efference copy will be driven by the active compensation for the press of the viewing eye ( suggested by wenshun li of columbia university ) .
presses on the viewing or the covered eye could be used to recover the internal proprioception and efference copy signals by algebraic reconstruction of the measured signals ( bridgeman and stark 1991 ) .
the resulting gains were 0.61 for efference copy and 0.26 for proprioception ; even with perfect summation of the gains at 0.87 , the brain would underestimate how far the eye really moved .
in fact it accounts for previously unexplained data on the perceived deviation of an eccentric target from the midline ; targets are perceived as more eccentric if their position is judged in peripheral vision , with the eyes straight ahead , than if they are fixated ( morgan 1978 ) . the gain from morgan  s data is 0.13 , precisely the 
efference copy , proprioception , and illusion gains sum to 1.00 , closing the circle on the signals used to register gaze position and consequent perceptions .
two centuries of work had led to the conclusion that efference copy dominates ; we can now see that the reason for the domination is that its gain is about 2.4 times greater than the proprioceptive gain .
thus efference copy explains a wide range of results and clinical observations better than proprioception .
efference copy clearly can not support space constancy , but for years no alternative was available .
o'regan ( 1992 ) asserted that there need be no memory for the content of previous fixations , because the information remains in the world and can be reacquired whenever an observer wants it .
we knew by then that no brain area contained a panoramic , high - acuity representation that corresponds to our spatially stable perception .
calibration solution : spatiotopic positions are calculated anew from proprioception , efference copy , and retinal sources for each fixation .
previous fixation positions are not taken into account ; the world appears to be in the same place because nothing tells the brain that it is not .
an elaboration of this idea was motivated by data showing that a saccadic target object that is present continuously appears to be stabilized , while objects that are interrupted near the time of a saccade appear to jump , even if it is the continuous target that really jumps ( deubel et al 2004 ) . to explain this , deubel et al
conclude that , before a saccade is executed , attention shifts to a reference object whose location and attributes are stored in a transsaccadic memory .
information from the previous fixation is discarded or ignored , and localization proceeds using currently available information .
other objects are then localized relative to the reference object . only if the object is not found
. evidence for this position comes from a number of sources , including change blindness , the difficulty of identifying changes in naturalistic scenes if they are masked by a brief blank ( simons 1996 ; rensink et al 1997 ) .
the importance of change blindness is that inattention to previous images prevents their interfering with present perception .
little is carried over from one fixation to the next ; we do not build a visual world by pasting together samples calibrated with efference copy , but simply perceive what is currently available , plus a gist and a few previously attended objects .
the stable , rich visual world of our perception is more promise than physiological reality .
 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 . 
Efference copy
Limitations of efference copy
Modern alternatives