One explanation is based on 
eye movements and the 
resulting retinal image thereby 
created. Suppose the eyes move 
back and forth in synchrony 
with the moving figure. The 
result would be that an image of 
the slit would be spread over 
the retina. Because the figure 
behind the slit is moving, 
different portions of it would be 
successively visible through 
the slit. Therefore, an extended 
image of the figure would be 
spread over the retina. So the 
explanation of the anomalous 
effect is simple. As in normal 
form perception, an extended 
image is present on the retina. 
True, it is not present 
simultaneously, but, given the 
known fact of visual 
persistence after a stimulus is 
no longer present, if the figure 
(and eyes) move fast enough, 
the extended image would be 
equivalent to a simultaneous 
extended image. The effect 
would be rather like that seen 
when a glowing cigarette is 
moved rapidly in a dark room. 
Its entire path is perceived 
simultaneously. This then is 
the peripheral theory.

    There are many difficulties 
with this view (although there 
is also some evidence 
supporting it). Why, for 
example, should the eyes move 
back and forth, unless possibly 
because the figure is perceived 
and the eyes seek to track some 
region of it. In that case, 
however, the eye movement is a 
consequence, not a cause, of 
the figure perception.

    In any event, we have been 
able to show in our laboratory 
(as have others) that the 
anorthoscopic effect occurs 
without any eye movement. 
Thus, the effect is indeed 
anomalous, a succession of 
differing contours all falling on 
a narrow column of the retina 
somehow leading to the 
veridical perception of a 
moving figure. A central theory 
seems to be required here. 
First, the perceptual system 
must detect, or otherwise have 
a preference to perceive, a 
figure moving at right angles to 
the slit rather than contour 
elements moving up and down 
the slit, as in the barber-pole 
effect (Chapter 7). The figure 
must possess certain 
characteristics before 
perception of an extended 
figure will occur. A straight 
line will not do. Once the 
perceptual system interprets 
the event appropriately, as an 
occluded object moving at right 
angles to the slit, it can 
reconstruct the figure from the 
set of successive directions 
that constitute it. This is then 
an example of a central theory.