Arbitrary Match-to-Sample in the Rat via Olfactory Stimuli in an Open-Field Apparatus

Abstract

Some organisms have the ability to discriminate between physically dissimilar environmental stimuli and place them into various abstract categories; this process of perceiving various stimuli as being somewhat equal to each other strongly suggests that the organism may be capable of higher-order symbolic processes. If after these categories are formed, three mathematical properties (reflexivity, symmetry, and transitivity) emerge, we call this capability “stimulus equivalence” (Sidman, 1982). After encountering multiple stimuli belonging to one particular equivalence class, if the organism is capable of stimulus equivalence, novel stimuli can be quickly and easily placed into the equivalence class without expending valuable time and energy; thus, this cognitive ability can be very useful in the survival of the organism. Recently, psychologists have investigated the ability of various species to demonstrate stimulus equivalence; the present study investigated this ability in two rats using olfactory stimuli. Subjects were trained to retrieve food pellets by removing scented lids from cups filled with sand, which were randomly arranged in an open-field arena. By training two sets of conditional discriminations via an arbitrary match-to-sample procedure, experimenters hoped to test for the emergence of properties argued by Sidman to be necessary and sufficient evidence of stimulus equivalence. Results showed both subjects were able to learn the fist conditional discrimination. The use of olfactory stimuli was an improvement over previous procedures involving learning in rats that used visual stimuli, and the odor arena appears to be a useful apparatus for studying complex learning in rats. While we were unable to demonstrate stimulus equivalence in the current study, we plan to extend the research to test the animals further.