One approach to the problem 
is to consider apparent motion 
as a special case of real motion 
and to explain the perception 
as the result of motion-detector 
neurons firing in the visual 
nervous system. If the 
successive stimulation of 
adjacent retinal cells leads to 
the rapid firing of neurons that 
are specialized to detect such 
stimulus motion, then the 
successive stimulation of 
retinal cells that are farther 
apart may cause the rapid firing 
of neurons that detect the 
stroboscopic stimulus 
sequence.

    Horace Barlow and William 
Levick at the universities of 
California and Cambridge have 
shown that precisely such a 
successive stimulation of 
neighboring, but not directly 
adjacent, regions of a rabbit’s 
retina will trigger the response 
of neurons in its visual nervous 
system.

    We might regard this 
approach as a sensory theory of 
apparent movement. While a 
theory of this kind may provide 
the explanation of perceived 
movement under stroboscopic 
conditions in animal species 
lower on the phylogenetic scale 
(fish, for example), it is 
inadequate to explain how we 
perceive it. First, apparent 
movement can be seen across a 
considerable angular distance, 
far enough for it to be unlikely 
that the two stimulated regions 
of the retina would be 
associated with the same 
motion-detector neuron in the 
brain. We can see such motion 
when a stimulus, A, falls on 
one side of the retina and a 
second stimulus, B, on the 
other. In fact, this probably 
occurs often, such as when the 
eyes are fixating between A and 
B. Under such conditions, A is 
projected to one hemisphere of 
the brain and B to the other. As 
can be seen in the illustration 
in Chapter 1 of the projection of 
neural fibers from the retina to 
the visual cortex, the only 
connection is through neurons 
that cross in the structure of 
the brain known as the corpus 
callosum.