Blocking and overshadowing in two species of fish.

In Experiment 1, a mixed blocking-overshadowing effect of color on an auditory discrimination was demonstrated in goldfish. In Experiment 2 (with lines differing in color and angle), blocking of angle by color and of color by angle was demonstrated in goldfish, In Experiment 3 (again with lines differing in color and angle), overshadowing of angle by color was demonstrated in carp, but the same animals (like goldfish in a previous study) failed to show greater intradimensional than extradimensional transfer. These results are consistent with the hypothesis that blocking and overshadowing are general phenomena of vertebrate learning. They suggest also that the processes responsible for blocking and overshadowing are different from those which produce the dimensional transfer effect.