What They Did
The researchers studied the ability of wild Western
Australian magpies to distinguish quantities. The magpies live in groups of 3
to 15 in urban semi-natural areas and are accustomed to humans. Individual
magpies were separated from their group, either by waiting for them to wander
off naturally or by distracting the other group members. The bird under study
was then presented with a randomized sequence of choices between two boards:
one with two strips of cheese and the other with two, three, four, or five
strips. Over the course of the experiment, 42 birds were tested, each being
offered the four choices 15 times on separate days.
The researchers found
that the birds chose the larger amount of food more than half the time, with
better performance correlated with greater differences between the amounts.
They also found that birds that lived in smaller groups were more likely to
choose five strips of cheese over two, but the group size had no effect for the
other combinations. The correlation between “correct” choice likelihood and
difference between the choices suggests that the birds decide based on ratio
rather than absolute number, with the smallest ratio (i.e. 2:5) easiest to
detect.
The researchers also propose two hypotheses for the effect
of group size. Smaller groups may offer less protection in intergroup
conflicts, making it important to compare the size of rival group. Smaller
groups also have fewer individuals watching for predators, so it’s more
important to maximize the benefit of limited foraging time.
Further Exploration
The researchers describe two cognitive systems animals use
to process quantity information: the object-file system tracks each object and
works for small numbers, while the approximate number system provides a general
idea of which group is larger. This seems to be the case for humans too.
Automatically knowing how many objects are in a group in called subitizing (see
https://hechingerreport.org/proof-points-subitizing/).
Perceptual subitizing means seeing the number of objects “all at once.” For
humans, the maximum is typically 4 to 6 objects.
Larger numbers, however, can be subitized by mentally dividing
the array into groups and subitizing the number in each group, such as seeing
three groups of four and knowing there are 12 objects without thinking about
counting or multiplication. This process is called conceptual subitizing.
Subitizing sounds as if it might be analogous to the object-file system
described in animal cognition, and of course humans also seem to have an
approximate number system. We can tell which group of items contains more, and
we’re better at it if there’s a greater difference between them.
Humans can also count one by one, as long as we have the
patience for. A lot of animals deal with quantity in a lot of different ways
(see https://www.quantamagazine.org/animals-can-count-and-use-zero-how-far-does-their-number-sense-go-20210809/),
but I haven’t seen any evidence that they can count symbolically and indefinitely
the way humans do. It would also be interesting to see how animals handle
number when the objects are dissimilar or when distractor objects are included,
but that’s a rabbit hole for another day!
No comments:
Post a Comment
Please be nice.