Many animals including scrub jays \citep{Clayton:2007fh},
ravens \citep{bugnyar:2016_ravens},
goats \citep{kaminski:2006_goats},
dogs \citep{kaminski:2009_domestic},
ringtailed lemurs \citep{sandel:2011_evidence},
monkeys \citep{burkart:2007_understanding, hattori:2009_tufted}
and chimpanzees \citep{melis:2006_chimpanzees,karg:2015_chimpanzees} reliably vary their actions in ways that are appropriate given facts about another’s mental states.
What could underpin such abilities to track others’ mental states?
Hare et al (2001, figure 1)
In this experiment by Brian Hare and colleagues, a subordinate chimpanzee makes predictions about a
dominant chimpanzee’s ability to retrieve food. They found that the subordinate’s predictions take
into account whether the dominant’s view was blocked while the food was placed. This could be
explained by the Third Principle. For the subordinate to predict that the dominant will not be able
to recover the food, it is sufficient to think: because the dominant did not encounter the food,
she will not be able to retrieve it.
‘In informed trials dominant individuals witnessed the experimenter hiding
food behind one of the occluders whereas in uninformed trials they could
not see the baiting procedure. In misinformed trials, dominants witnessed
the experimenter hiding food behind one of the occluders, and once the
dominant’s visual access was blocked, the experimenter switched the food
from its original location to the other occluder’ \citep{Hare:2001ph}.
Clayton et al, 2007 figure 11
Clayton et al, 2007 figure 12
‘the jays were much more likely to re-cache if they had been observed by a conspecific while they
were caching than when they had cached in private. By re-caching items that the observer had seen
them cache, the cachers significantly reduce the chance of cache theft, as observers would be unable
to rely on memory to facilitate accurate cache theft’ \citep[p.~516]{Clayton:2007fh}.
Bugnyar et al, 2016 figure 1
First show that window open vs window closed affects caching behaviour.
Then familiarise ravens with the peephole, letting them use it while humans
cache and letting them ‘steal’ the human-cached food.
Now test them by allowing them to cache when there’s apparently (from the sound,
which is actually a recording)
a raven on the other side.
Bugnyar et al, 2016 figure 2a
Conclusion 1:
‘Peephole designs can allow researchers to overcome the confound of gaze cues’ \citep{bugnyar:2016_ravens}.
‘ravens can transfer knowledge from their own experience in a novel context---using peepholes to look
into an adjacent room---to a caching situation in which they can hear but not see a conspecific in that
room’ \citep{bugnyar:2016_ravens}.
Bugnyar et al, 2016 figure 1