I'm a contributor to Very Short List: Science, the latest offshoot of the VSL brand. (David Dobbs is another contributor.) For those who don't know, VSL is a very short email on something interesting sent daily to your inbox. We recently featured this paper in the Science channel:
We've always known that rats were capable of complex thought: They memorize mazes and form elaborate social hierarchies. Now we're learning that they seem to think about thinking itself. Until recently, that crucial skill -- called metacognition -- was believed to be unique to humans.
Scientists at the University of Georgia tasked rats with identifying "short" and "long" noises. Rodents that answered correctly were given six food pellets; those that answered wrong got nothing. So far, so Pavlovian. But the rats were also given a third option: If they declined to take the test, they received three food pellets. Most of the rats refused to identify the noises that were hardest to classify -- thus suggesting a surprisingly evolved sense of their own knowledge and abilities. It's something to think about the next time you reach for the rat poison.
For more on metacognition, check out my recent articles on the tip-of-the-tongue state and the presidential race.
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How do they know that the rats don't just press the third button when then think the sound is of medium length?
Allison L. Foote and Jonathon D. Crystal, principal authors of the study, said that classification of noises in the middle of the range is difficult, but they compared accuracy during the discrimination lenght and forced choice task, leading them to reject an alternative hipothesis to metacognition in rats.
That is, in their words: "An important feature of the design of this study is that
we evaluated accuracy on trials in which the rats were
forced to take the test. Moreover, the rats initiated these
forced tests in the same manner as they initiated choice
tests (i.e., with a nose-poke response). These factors
limit the ability of alternative hypotheses to explain our
data. For example, the forced duration tests are unlikely
to have been unexpected and thereby unlikely to have
disrupted accuracy. If forced choices had been surprising,
we would expect longer latencies to respond in
forced tests relative to choice tests. However, there
was no evidence for a difference in the latency to respond
with either a nose-poke (t[2] = 1.1, p > 0.05;
mean 6 SEM: 0.61 6 0.19 s and 0.80 6 0.12 s for choice
and forced tests, respectively) or lever-press response
(t[2] = 0.4, p > 0.05; mean 6 SEM: 2.70 6 0.47 s and
2.65 6 0.28 s for choice and forced tests, respectively).
Consequently, the accuracy difference on forced and
choice tests was not likely to be due to performance disruption
from unexpected forced tests."
I'm going to sign up for VSL - thanks for the tip.
How did the rats signify their refusal to take the test?
David: The rat presses a third bar.
Metacognition in rats is, from what I can tell, a very controversial topic. A guy who looks at metacognition in chimps recently gave a talk at my school and he was extremely critical of the work on rats. He said their results could be readily accounted for by instrumental conditioning.
There's also a recent paper in Nature that says the same thing: dx.doi.org/10.1038/nature07200
I tend to agree.