Once the alternative is 
achieved—–or what amounts to 
the same thing, when subjects 
are initially told about the 
alternatives—–the situation is 
entirely different 
psychologically. Now the 
observer knows that the figure 
is reversible, and the 
alternative perceptions are 
represented in memory. 
Therefore, merely thinking 
about the alternative not being 
perceived at any given moment 
may suffice to lead to a 
perceptual reorganization in 
which it is perceived. In short, 
the explanation of reversal in 
the case of informed observers 
may have more to do with an 
intention to reverse and a 
shifting memory reference 
than with neural fatigue. 
However, as noted above, the 
fatigue theory cannot be ruled 
out as a contributing factor; 
some evidence supports it.