The degree to which nonhuman animals recognize 2D images as representing the corresponding real objects remains debated. The common marmoset monkey (Callithrix jacchus) is often cited as a species which spontaneously shows natural behaviors to 2D images, e.g. grabbing behaviors to insects and fear responses to snakes. In this study, ten marmosets from two different groups were tested with a live cricket, a 3D plastic model, a monochrome image and two video recordings of the cricket. The monkeys showed the grabbing behavior to the real cricket and the 3D plastic model, but to none of the 2D images. Our experiment suggests that depth information is the most important factor eliciting predatory behavior from the marmosets. In behavioral experiments, monkeys' responses toward 2D images of real objects should be carefully interpreted. All session videos are uploaded here with a 'LOG.txt' file which has sessions & timestamps when coded behaviors occurs.

This study was funded by Bundesministerium fur Wissenschaft, Forschung und Wirtschaft, IS761001 to W. Tecumseh Fitch, Thomas Bugnyar and Ludwig Huber.