Value transfer in simultaneous object discriminations by rats

Abstract

Increasing the amount of sunflower seeds under a baited object when it occurs either within or external to a simultaneous object discrimination increases the value transferred to the nonbaited object. Rats were trained with two object discriminations, A1B0 and C1D0, where the superscript refers to the number of sunflower seeds obtained for pushing aside the object. The amount under A was increased to six on other trials in which the A6 or C1 object alternated with regular A1B0 or C1D0 discrimination trials. The A and C objects on the alternating trials were presented alone (Experiment 1), with a common nonbaited object (A6X0 and C1X0; Experiments 2 and 3), or with two different nonbaited objects (A6X0 and C1Y0; Experiment 4). Subsequent probe tests with pairs of usually nonbaited objects (e.g., B1D1, X1Y1) showed that the rats preferred B to D in Experiments 1-3, but not in Experiment 4, where they preferred X to Y. These preferences cannot be accounted for solely by differential inhibition, because initial training with only A1B0 and C1D0 discriminations in three of the four experiments prevented the rats from making or greatly reduced their making more nonreinforced responses within the C1D0 than within the A1B0 discrimination. Therefore, these preferences must be considered to reflect a value transfer effect. Other preference probe tests between X or Y and B or D in Experiments 2-4 revealed a possible differential inhibition effect, however, since the rats preferred a more recently introduced nonbaited object to an originally presented nonbaited object regardless of which baited object had accompanied it.