Pigeon reaction time, Hick's law, and intelligence

Pigeons' choice reaction times (RTs) increased as a linear function of log2 number of potential target stimuli (Experiments 1-3), as would be predicted by Hick's law. The values of intercepts and slopes decreased with training (Experiments 2 and 3) and with differential reinforcement of short RTs under percentile reinforcement contingencies (Experiment 3). RT functions obtained from human subjects were also consistent with Hick's law, but slopes for pigeons were significantly lower than those for humans (Experiments 4 and 5). These results extend the generality of Hick's law to pigeons but are inconsistent with Jensen's claim that the parameters of the Hick function are related to intelligence.