Wednesday, June 20, 2012

Haun and Call: "Great apes’ capacities to recognize relational similarity" (2009)

In an attempt to map the evolutionary history of analogical reasoning, this paper compares the performance of children to apes on a selection task. The task is supposed to measure the ability to recognize "relational similarity," i.e., identifying a cup by its position relative to other cups.

The Chimpanzee Experiment

The set-up is this: An experimenter hides an object in one of three cups in his end of the table; the participant then has to find an identical object in one of three cups in the other end. However, the three cups are closer together in the experimenter's end of the table, and also aligned so that proximity clues conflict with relative position clues:

There are two additional conditions that I am not considering here: One in which the three cups are connected with plastic tubes to suggest that the object can roll from one cup to another, and another condition in which they are connected by strips of gray tape, suggesting a structural parallel.

In the task with no clues, chimpanzees seem to choose the "right" cup above chance levels (p. 155). This is taken as evidence of an ability to recognize relational similarity.

A Bias Reading

I personally feel a little reluctant about counting the cup on the far left as the only "correct" choice, although it will certainly begin to appear more and more so as the system gets established through repeated trials.

However, the proximity argument suggesting the "wrong" cup is not necessarily a wrong argument in all real-life situations. What the experiments shows is thus, I think, that chimpanzees have a taxonomic bias that orangutans do not, i.e., chimps prefer one-to-one mappings even when they conflict with proximity clues.

Children, on the other hand, show a marked bias towards the middle cup wherever the experimenter hides the target object. None of the apes seem to have this symmetry bias.

A Possible Process Analysis

A hierarchical Bayesian model might peel these biases apart by identifying the following levels of modeling:
  1. Pr(a), the absolute probability of finding the target object in cup a, regardless of where the experimenter hid it.
  2. Pr(a|x), the conditional probability of finding the object in cup a, given that it was hidden in cup x.
  3. Pr(a|x,m), the conditional probability of finding the object in cup a, given that it was hidden in cup x and that the experimenter is using a mapping m.
All of these layers can in principle be informed by prior knowledge. For instance, (1) might exhibit a symmetry bias, (2) a proximity bias, and (3) a taxonomic bias.

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