Effects of number of items on the pigeon's discrimination of same from different visual displays

The pigeon's discrimination of visual displays comprising from 2 to 16 computer icons that were either the same as or different from one another was studied. Discrimination of Same from Different displays improved when the displays contained more icons, both after training with just 16-icon displays (Experiment 1) and after training with 2-, 4-, 8-, 12-, and 16-icon displays (Experiment 2). That improvement was specific to displays of different icons; accuracy to displays of same icons did not differ as a function of icon number. These results were well described by the degree of variability or entropy in multielement visual displays.