Source Paper
Information, certainty, and learning
Harris JA, Gallistel CR
eLife • 2026
Classical Conditioning with Variable CS-US Intervals
Objective: To measure classical conditioning acquisition using variable CS-US intervals with different temporal relationships between conditioned stimulus and food reinforcement
Protocol Steps
Housing and food restriction
House rats in groups of 4 and implement food restriction 3 days before experiment
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“Three days before commencing the experiment, they were placed on a restricted food schedule”
Daily feeding schedule
Feed rats daily ration 30 minutes after training session
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“half an hour after the end of the daily training session, each tub received a ration”
Group assignment
Randomly allocate each tub of four rats to one of 14 experimental groups
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“Each tub of four rats was randomly allocated to one of the 14 groups”
Skip magazine training
Begin experiment without preliminary magazine training
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“The rats were not given magazine training. The experiment commenced with the first conditioning session”
Implement variable CS-US intervals
Use uniform distribution for CS-US intervals centered on group-specific T value
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“the CS-US interval varied from trial-to-trial according to a uniform distribution centred on the value of T”
Set interval parameters
CS-US intervals range from 2s minimum to 2×T-2s maximum
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“the interval varied from a minimum of 2 s to a maximum of 2x T –2 s”
Configure inter-trial intervals
Use variable ITIs with uniform distribution and 15s minimum
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“The ITI in each group also varied from trial-to-trial as a uniform distribution with a minimum of 15 s”
Set trial numbers per session
Use 10 trials per session for groups with C/T ratios 1.5-72, and 3 trials for higher ratios
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“For the first 11 groups, there were 10 trials per session; for the remaining three groups, each session contained only three trials”
Conduct training sessions
Train all groups daily for 42 consecutive sessions
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“continued for 42 sessions over 42 consecutive days”
Record magazine entries
Monitor photo-beam interruptions during CS and ITI periods
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“Photo-beam interruptions by entry into the magazine were recorded during each CS and each ITI”