A test of the conservation model for autoshaped leverpressing and polydipsia in the rat

This study examined a conservation model (Allison & Mack, 1982) that predicts a linear relation between the weighted sum of two responses, autoshaped leverpressing and polydipsia, and the amount of food delivered on a variable-time schedule. Fifteen rats were assigned randomly to one of three groups. The rats in Group 1 were maintained at 80% of their free-feeding body weights. Those in Group 2 began at 100% but were allowed to lose weight during the experiment. The rats in Group 3 also began at 100% of their free-feeding weights and were maintained at this level. Each group was exposed to five conditions that delivered less food than that consumed during baseline and to one condition that delivered more food. The results did not support the conservation model. Contrary to the model, the decreasing linear relation between the individual responses, or the weighted sum of the responses, and the amount of food delivered was not found for all rats, and some rats responded more when an excessive amount of food was presented than during baseline.