In a companion experiment, 
we kept the tank stationary 
while rotating the drum. Now 
the fish swam vigorously in the 
direction of the drum’s motion, 
keeping pace with it, even 
though there was no current. 
This condition would be 
regarded as the optomotor 
paradigm, whereas the one 
with the rotating tank and 
stationary drum would not. But 
they are psychologically and 
behaviorally identical. They 
both illustrate that a 
surrounding visible structure, 
when moving, generates or 
induces an experience of self-
motion, while the structure 
itself appears to be stationary. 
In an animal such as a fish, 
that experience in turn 
generates a tendency to 
compensate for such unwanted 
movement of the self; the 
animal attempts to maintain its 
position in its perceived world. 
In a human observer, the self-
motion seems to be tolerated; it 
elicits no behavior designed to 
nullify it, at least in an 
experimental situation. (In a 
more natural situation, such as 
in a river, a person might well 
react as the fish does, by 
swimming upstream in order 
not to be carried away 
downstream.) The optokinetic 
response is undoubtedly 
motivated by the tendency to 
stabilize the moving image, but, 
according to the present 
hypothesis, it has nothing to do 
with induced self-motion. It 
occurs both when the drum 
appears to be rotating and the 
self is stationary and when the 
drum appears to be stationary 
and the self is experienced as 
moving.