Last week I posted a story about an experiment suggesting monkeys can recognize themselves in the mirror. One of the experts I contacted was Peter G. Roma, who was the lead author of a 2007 paper that failed to find evidence for this kind of self-recognition. Roma responded today with an interesting response, which I’m posting here, and at the end of the original post.
Although the video samples are provocative, I cannot agree with the conclusion (and title) of the paper.
The lack of social behaviors towards the mirror is irrelevant because the monkeys all had an extensive history with mirrors prior to the study, so there was no reason to expect social responses after years of habituation to reflective surfaces. To anthropomorphize, they may still think the monkey in the mirror is another animal, but over the years they’ve learned that he’s harmless.
The examples of putative genital viewing were not convincing either. The authors repeatedly asserted that the monkeys used the mirrors to view areas they could not see directly, but monkeys can see their genitals unaided, and they play with them all the time with or without mirrors! Even the video samples show the monkeys looking at their genitals directly then viewing the same area(s) in the mirror. This is why scientists do the mark test!
In my view, the most compelling evidence was the first video of the monkey touching the head implant while holding the mirror. There is no doubt that the monkeys could not see the implant without a reflective surface, but the key here is whether or not this self-examination behavior occurred more frequently in the presence of the mirror vs. without. The authors report increased incidence of touching “unseen” areas in the presence of the mirror (figure 2C), but these data include touching the cranial implant and the genitals. I suspect these data are artificially inflated by what the authors perceive as mirror-guided genital examination, which even in the video examples did not appear to be anything more than typical stereotyped “acrobatic” behaviors often seen in individually-housed rhesus monkeys. The authors provide no data on the frequency of just cranial implant touching with vs. without mirrors, and no visual evidence except for the single incident from the video. Why wouldn’t they report the number of implant explorations independently of the genital viewing?
My primary concern is that all monkeys failed the mark test, and the strongest apparent evidence of mirror self-recognition (MSR) was only seen in two monkeys following cranial surgery–a manipulation with strong tactile cues that could elicit exploration regardless of the mirror’s presence. Their argument rests largely on the assertion that the cranial implant is a “super mark” that somehow awakened a latent ability in the monkeys to self-recognize, but it’s unclear why the implant would be more visually salient than a brightly contrasting color marking on the face. The more parsimonious conclusion is that the tactile sensation of the implant was enough to elicit exploration, but even then, the authors provide no evidence that implant exploration occurred more frequently in the presence of the mirror vs. without.
If the authors’ hypothesis is true that a cranial implant serves as a “super mark,” then their procedures warrant replication, which frankly they should have done before making such a bold assertion. Currently within the Order Primates, the overwhelming preponderance of evidence still limits MSR and the fundamental cognitive precursor to a “sense of self” to the apes.
Originally published October 11, 2010. Copyright 2010 Carl Zimmer.