Discrimination of compound stimuli involving the presence or absence of a distinctive visual feature.

Pigeons pecked a key for food. The key showed two kinds of pictures. One picture had a special mark. The other looked the same but the mark was gone.

Birds learned go/no-go: peck when the mark is there, hold still when it is missing. The team then checked how the birds reacted to new pictures that looked almost the same.

Reinforcement history shaped later choices. Birds that got food for pecking the marked picture pecked faster to any picture close to it.

When the mark was missing, pecking dropped. The drop followed a smooth curve, showing clear generalization.

Snapper et al. (1969) ran a similar pigeon study two years earlier. They used color-form mixes and saw form cues win over color. Both papers show compound pictures steer pigeon behavior, but the 1969 task was conditional while this one was go/no-go.

Catania (1973) came next and added that pigeons use both cues if both predict food. The 1971 data fit right in: birds tracked which part of the picture mattered for payoff.

Bennett et al. (1973) seems to disagree. They found compound samples hurt matching accuracy. The clash is only skin-deep. Their birds had to pick a comparison after seeing the sample, a harder task. Go/no-go is simpler, so compounds helped here but hurt there.

Your client also faces compound cues: a red card plus the word STOP, or a beep plus a light. Reinforce the right combo early and you will see clean discrimination later. If you mix in too many extras, switch to a matching task, or demand conditional choices, expect errors. Start simple, reinforce the key feature, then test generalization before you fade support.