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Updated: Jul 19, 2026

Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice
Published on: March 30, 2016
Effect of unconditioned stimulus magnitude on the emergence of conditioned responding
Richard W Morris1, Mark E Bouton
1Department of Psychology, University of Vermont, Burlington, VT 05401, USA.
Abstract:
Although unconditioned stimulus (US) magnitude influences conditioning, no experiment has addressed whether it influences a decision point at which the organism first responds (Gallistel & Gibbon, 2000). Two appetitive conditioning experiments with rats confirmed that the rate of food cup entries and proportion of head jerking were related to the number of pellets (US) provided after the conditioned stimulus. In addition, the onset of responding measured by the number of reinforcers to a criterion or by a quantitatively identified change point also reflected US magnitude. Two aversive conditioning experiments also found that the amount and onset of freezing were related to footshock intensity. All experiments identified a trial at which responding increased abruptly in individual subjects. However, the point where the increase occurred was earlier with larger USs.
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