Similar stimulus features control visual classification in orangutans and rhesus monkeys.

Scientists tested two monkey species on the same picture-sorting task. Rhesus monkeys and orangutans saw photos on a screen. They had to tap the picture that matched a sample.

The team kept every detail the same for both species. Same photos, same order, same rewards. They wanted to see if the animals used the same visual cues to choose.

Both species sorted pictures the same way. They paid attention to big shapes and tiny details at once. No species was better or faster.

The monkeys did not rely on just one cue. Color, outline, and small patches all guided their choices together.

Nevin (1967) also used rhesus monkeys in a lab. That study taught line-tilt slowly and found sharper learning. The new study shows the same animals can juggle many picture cues at once.

Madsen et al. (1968) worked with pigeons on shape tilt. Pigeons showed wide, bumpy generalization. The monkeys showed tight, mixed control. The difference is species, not method.

McIntire et al. (1987) built equivalence classes with monkeys. They needed many training trials. Here, no extra training was needed for the animals to group photos. The tasks differ, so both results stand.

If you teach visual discriminations, use many cues together. Monkeys—and likely humans—blend global and local features. You can speed training by highlighting both large shapes and small details in your materials.