Mediated overshadowing and potentiation of long-delay taste aversion learning: Two versus six cue-taste pairings

Mediated overshadowing occurs when an evoked representation of one stimulus interferes with the formation of an association between two other stimuli. This study tested whether such an effect can be found in long-delay taste aversion learning. The general methodology was to pair a cue with a sour taste (hydrochloric acid [HCl]) and then introduce the cue during the delay between the target taste, sucrose, and injection with lithium chloride (LiCl). Either 2 or 6 cue-HCl pairings were given. In Experiment 1, introduction of the cue, an almond flavor, produced overshadowing of the sucrose aversion in the group given 2 cue-HCl pairings (Paired-2), relative to an unpaired control, but potentiation of the sucrose aversion in the group given 6 cue-HCl pairings (Paired-6). This confirms that few pairings can be better than many in determining whether representation-mediated effects occur (Holland, 1990). A possible explanation for the Paired-6 results is that almond evoked an aversive response rather than memory of the sour HCl and that this added to the aversion produced by the sucrose-lithium pairing. Experiment 2 obtained similar results when a context was used as the cue intended to evoke an HCl representation.