Conceptualization without specific training in squirrel monkeys (Saimiri sciureus): A test using the non-match-to-sample procedure.

We report evidence that monkeys are able to categorize various pictures into conceptual classes without specific training for most of the conceptual classes involved. This was shown with a variation of the non-match-to-sample procedure: Each squirrel monkey was shown one picture as sample and, thereafter, two other pictures, one of which belonged to the same conceptual class as the sample and the other of which did not. To solve a trial, it was necessary to make a same–different judgment between the stimuli, that is, to view the sample and one response stimulus as "same." The conceptual classes tested included humans, monkeys, some nonprimate animal species, apples, bananas, trees, letters, telephones, various geometrical forms, and the concepts of sameness and numerousness. On the average, all monkeys performed with only few errors on the task. Their errors compare well in number and in quality with those performed by 3 human subjects tested under comparable conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)