Effects of the intertrial interval on taste-aversion learning in rats

Variations in the intertrial interval (ITI) between two taste-aversion conditioning trials indicated that more saccharin-aversion learning occurs with longer ITIs (Experiments 1, 2 and 4). Two conditioning trials separated by 35 min did not produce stronger taste aversions than a single saccharin-lithium pairing; however, stronger conditioning was evident when the two trials were administered with a 3-day intertrial interval. Independent evaluation of saccharin and lithium exposure as possible sources of proactive and retroactive interference suggested that poor conditioning at short ITIs occurs because lithium treatment during Trial 1 interferes with conditioning during Trial 2 (Experiment 2). Assessments of the unconditioned suppression of activity (Experiments 3) and novel-fluid intake (Experiment 4) indicated that drug treatment was effective during both conditioning trials regardless of the intertrial interval. Furthermore, with a 35-min ITI (but not with a 3-day ITI) drug treatment in Trial 1 persisted long enough to summate with the unconditioned responses to drug treatment in Trial 2. These findings are consistent with the idea that with short ITIs the lingering effects of the US from Trial 1 overshadow or mask the CS flavor in Trial 2, and this interferes with the conditioning that Trial 2 would otherwise produce.