The Goal Units Dimension in Negative Contrast Failures with Sucrose

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Abstract
To pursue the possibility that the usual failure to obtain the successive negative contrast effect (SuNCE) with sucrose rewards is an indirect consequence of the liquid medium in which sucrose is usually delivered, Experiment 1 was designed to look for the SuNCE with sucrose pellets. Food-deprived rats were trained for 20 preshift days, two trials/day in a runway for either one or 12 45-mg Noyes pellets of either sucrose or standard formula. During six postshift days, 10 trials/day, all rats were given the one-pellet reward of the same preshift type, and the SuNCE appeared in the standard but not sucrose groups. A second experiment produced single-alternation patterning in the discrete-trial lever pressing of rats given four two-trial sequences of one or 10 sucrose or standard pellets each day for 102 days. The patterning was potentiated with a change, for the remaining 28 days, from the one-pellet reward to nonreward, but in no case throughout the experiment was the strength of patterning any different for sucrose and standard pellets. That patterning but not the SuNCE was demonstrated with sucrose pellets is taken as evidence that the two phenomena are mediated at least in part by different processes, and that the mechanism may not be generalization decrement.