ASSOCIATION AND COLOR DISCRIMINATION 457 



1. Do the fishes studied discriminate colors? 



2. If SO, is the discrimination due to wave-length or to in- 

 tensity? In other words, do fishes see colors as such, or as 

 shades of gray? 



3. If the eyes of fishes are affected by differences in wave- 

 length, is their color vision like that of a normal human being? 



4. Can fishes form associations with colors? 



5. Would such associations be of value to them in their struggle 

 for existence? 



6. How do the results agree with present theories of color 

 vision? 



The following series of experiments were aimed to answer 

 these questions and to supplement the evidence furnished by 

 other workers. They were planned with a view to training 

 fishes to secure food in particular ways, and extended through 

 three years. 



The general problem presented to the fishes was that of learning 

 to associate food with a certain color and at the same time asso- 

 ciate unpalatable substances such as paper with another color. 

 The mudminnow and the stickleback are both shallow-water 

 fishes which discover their food largely by sense of sight. Va- 

 rious methods of presenting food were tried. Considerable 

 time was consumed at the beginning by using colored electrodes. 

 These were thrust into the water at the sides of the dish and 

 food was offered on forceps in the water. The fishes were given 

 a mild electric shock when they snapped at bait on the wrong 

 color. This method had to be abandoned because one shock 

 often caused a fish to refuse food for several days. 



Instead of this, the fishes were fed on only one color, while 

 on the color with which unpalatability was to be associated, 

 they were offered balls of paper closely matching the food in 

 appearance and color. In order that there might be no chance 

 to smell the food, the bait was not dropped into the water, but 

 the fishes were taught to leap out of water regularly and take 

 it from forceps. Minced snail meat was the most attractive 

 bait in the long run, although this was varied at times with 

 chopped earthworms, slugs, and liver. Repeated trials deter- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 4 



