A new mark test for mirror self-recognition in non-human primates.
For 30 years Gallup's (Science 167:86-87, 1970) mark test, which consists of confronting a mirror-experienced test animal with its own previously altered mirror image, usually a color mark on forehead, eyebrow or ear, has delivered valuable results about the distribution of visual self-recognition in non-human primates. Chimpanzees, bonobos, orangutans and, less frequently, gorillas can learn to correctly understand the reflection of their body in a mirror. However, the standard version of the mark test is good only for positively proving the existence of self-recognition. Conclusive statements about the lack of self-recognition are more difficult because of the methodological constraints of the test. This situation has led to a persistent controversy about the power of Gallup's original technique. We devised a new variant of the test which permits more unequivocal decisions about both the presence and absence of self-recognition. This new procedure was tested with marmoset monkeys (Callithrix jacchus), following extensive training with mirror-related tasks to facilitate performance in the standard mark test. The results show that a slightly altered mark test with a new marking substance (chocolate cream) can help to reliably discriminate between true negative results, indicating a real lack of ability to recognize oneself in a mirror, from false negative results that are due to methodological particularities of the standard test. Finally, an evolutionary hypothesis is put forward as to why many primates can use a mirror instrumentally - i.e. know how to use it for grasping at hidden objects - while failing in the decisive mark test.
Heschl
Adolf
A
Konrad Lorenz Institute for Evolution and Cognition Research, Adolf Lorenz Gasse 2, 3422, Altenberg, Austria. adolf.heschl@uni-graz.at
Burkart
Judith
J
D000818:Animals; D001522:Behavior, Animal; D002144:Callithrix / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D008297:Male; D010775:Photic Stimulation; D012649:Self Concept