Molar vs Molecular Approaches to Reward Schedule and Serial Learning Phenomena

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In Experiment 1 all rats received identical series of rewarded and nonrewarded trials in a black runway and in a white runway. A grouping cue, a change in runway brightness, was introduced on a rewarded trial that followed either a single nonrewarded trial (Group N1) or four successive nonrewarded trials (Group N4). Over a series of four nonrewarded trials terminating in reward, Group N1 ran slower than Group N4 on Trial 2 but faster than Group N4 on Trial 4. In Experiment 2, slower running occurred when the grouping cue occurred on Trial 4 of a consistent reward schedule rather than on Trial 4 of a partial reward schedule. These findings were shown to be inconsistent with three theories that attempt to explain reward schedule data in terms of some overall characteristic of the schedule such as percentage of reward (molar theories). The data are consistent with the sequential view that recommends decomposing reward schedules into more elementary memory units (a molecular theory). In particular the data demonstrate that the effects of an overall reward schedule on behavior are determined by the more specific reward schedules associated with each memory component of the schedule. Importantly, the findings suggest that reward schedule investigations and serial learning investigations are, theoretically speaking, identical. Accordingly, the findings strongly discourage the common practice of reward schedule theories ignoring serial learning data and of serial learning theories ignoring reward schedule data.