Subjective value of risky foods for individual domestic chicks: a hierarchical Bayesian model |
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Authors: | Ai Kawamori Toshiya Matsushima |
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Institution: | (1) Laboratory of Animal Behavior and Intelligence, Department of Biology Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Sapporo 060-0810, Japan; |
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Abstract: | For animals to decide which prey to attack, the gain and delay of the food item must be integrated in a value function. However,
the subjective value is not obtained by expected profitability when it is accompanied by risk. To estimate the subjective
value, we examined choices in a cross-shaped maze with two colored feeders in domestic chicks. When tested by a reversal in
food amount or delay, chicks changed choices similarly in both conditions (experiment 1). We therefore examined risk sensitivity
for amount and delay (experiment 2) by supplying one feeder with food of fixed profitability and the alternative feeder with
high- or low-profitability food at equal probability. Profitability varied in amount (groups 1 and 2 at high and low variance)
or in delay (group 3). To find the equilibrium, the amount (groups 1 and 2) or delay (group 3) of the food in the fixed feeder
was adjusted in a total of 18 blocks. The Markov chain Monte Carlo method was applied to a hierarchical Bayesian model to
estimate the subjective value. Chicks undervalued the variable feeder in group 1 and were indifferent in group 2 but overvalued
the variable feeder in group 3 at a population level. Re-examination without the titration procedure (experiment 3) suggested
that the subjective value was not absolute for each option. When the delay was varied, the variable option was often given
a paradoxically high value depending on fixed alternative. Therefore, the basic assumption of the uniquely determined value
function might be questioned. |
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