Temporal map formation in appetitive second-order conditioning in rats.

Three experiments examined whether second-order conditioning resulted in the formation of a fully-featured temporal map, as proposed by the temporal coding hypothesis. Experiments 1 and 2 examined second-order conditioning with different first- and second-order relationships. Measures of the strength of second-order conditioning were mostly consistent with the temporal coding hypothesis; second-order conditioning was best with arrangements in which CS2 occurred prior to the time that the US normally occurred during CS1-US presentations. However, there was no evidence of anticipatory timing during CS2 during second-order conditioning. A third experiment directly examined whether a fully-featured temporal map was formed during second-order conditioning by examining the acquisition of anticipatory timing in subsequent reinforced second-order trials. The results of Experiment 3 suggested that the effects obtained in Experiments 1 and 2 were due to learning of the temporal order and coincidence of events that resulted in the formation of an ordinal temporal map, but that precise durations were not encoded.