Proximal, but not distal, pre-exposure reduces serial overshadowing in one-trial taste aversion learning

This experiment tested whether pre-exposing a taste would reduce its ability to overshadow conditioning to a target taste and whether this effect would depend on the delay between pre-exposure and conditioning. Two groups of rats were pre-exposed to an interfering taste (HCl) either a week before conditioning (Group Distal) or the day preceding conditioning (Group Proximal). In the single conditioning trial, rats were given the target taste (sucrose) and 65min later were injected with lithium. The groups differed as to what they were given to drink 50min after sucrose: The Distal, Proximal and Novel groups were given HCl, while the Control group was given water. Pre-exposure to HCl reduced overshadowing of the sucrose aversion by HCl in Group Proximal but not in Group Distal. Possible explanations for the latter result include extinction of the context-HCl association and loss of context control over an HCl-no outcome association.