Simultaneous processing of short delays and higher order temporal intervals within a session by pigeons

This study tests the ability of pigeons to process simultaneously two kinds of temporal intervals of the sort relevant in foraging problems: delays within trials on the order of seconds as well as 'higher order' intervals, on the order of minutes, within the session. Pigeons were given 20 min sessions of a chained VI 5 s-FI 10 s schedule reinforcement. A particularly large reinforcer was delivered either after 16 min or after 6 min, in a blocked design. In probe sessions no large reinforcer was given. The rate of responding in probe sessions following training with the early reinforcer showed a peak in rate of responding at about 6 min. In probe sessions following training with the late reinforcer, the rate of responding showed only a linear increase. In addition, empty trials using the peak procedure showed that the pigeons timed the FI 10 s within trials, as predicted by models of timing with two accumulators. Baseline sessions with no large reinforcer at the beginning of the experiment showed a bitonic function with slight changes in rates of responding.