Analogous experiments 
indicate that many species are 
able to achieve lightness 
constancy. In one experiment, 
for example, fish were first 
trained to push the darker of 
two buttons seen under equal 
illumination. Then, the darker 
button was placed under 
brighter illumination than the 
lighter button. Thus, under 
these conditions, the 
luminance of the darker button 
was greater: It reflected more 
intense light to the eye than 
the lighter button. 
Nevertheless, the fish 
continued pressing at the 
darker button. One may 
therefore infer that the fish 
continued to perceive that 
shade as darker and expected to 
receive food as a consequence 
of pushing it.