Concept formation -- as in being able to distinguish cats from dogs or to recognize the biological similarities between chimpanzees, gorillas and orangutans and categorize them accordingly -- is a way of organizing information based on visual cues, one that humans utilize from an early age. But we are not the only ones. Orangutans, and possibily gorillas, are able to organize information based on visual cues in the same manner as humans, according to new research published in the new open-access journal PeerJ.

The discovery goes against the view that concept formation is dependent on formal training and/or the ability to form verbal labels for such concepts.

Jennifer Vonk, an associate professor of psychology at Oakland University, built upon a previous study where she tested a group of orangutans' and a gorilla's ability to differentiate between different animal species by selecting images on a computer touch-screen. In that experiment, orangutans, but not the gorilla, appeared to learn intermediate level category discriminations, such as primates versus non-primates, more rapidly than they learned concrete level discriminations, such as orangutans versus humans

For the current study, Volk tested four of the same orangutans and the gorilla and tried to have them match images from the same species or family (i.e. one with a perceptual similarity).

In a second experiment, the researchers presented the apes with images of animals belonging to different taxonomic classes (insects, reptiles, fish, birds, and mammals). The apes were intended to match the images to sample images of other members of that class.

Presumably it would be more difficult for the apes to correctly match images from within the same taxonomic class, as there would be fewer dissimilarities in the images than there would be if they were of creatures from different taxonomic classes. Furthermore, if the apes were using a purely perceptual strategy to make their choices then they should find it more difficult to match images from the same taxonomic classes compared to matching images from the same species or family.

"However, the orangutans were actually able to match images from the same classes at a higher level of accuracy than they were able to match images from within the same species or family, indicating that they may have formed a concept for the class of animal that extended beyond perceptual similarity," Vonk said in a news release. "The gorilla was also able to acquire these concepts but required more testing sessions than with the concepts involving same species. The 'class level' distinctions are analogous to the basic level categories learned first by human children. Importantly, these apes had not been trained to match based on perceptual identity -- a procedure that might work against the likelihood that animals focus on broader concepts rather than perceptual features."

Vonk said the ability of other apes to match stimuli at the level of taxonomic class is "a novel finding that tells us that abstract categories can be extracted from visual stimuli in the absence of biological information, verbal labels, or extensive experience with the objects. This finding suggests that orangutans, and perhaps gorillas, may share an underlying conceptual process with humans."

Vonk added that the discovery of category-matching ability in non-humans goes counter to often-held claims that identifying biological categories is dependent on scientific knowledge or language.

"The findings are expected to inspire other investigators to test non-humans on increasingly abstract category tasks to further determine what features non-humans are using to solve such tasks, and whether the process is indeed similar to that used by humans to categorize novel items," Vonk said.