Conditioning the unconditioned response: Modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response

Conditioning-specific reflex modification (CRM) occurs when classical condi tioning modifies responding to an unconditioned stimulus (US) in the absenc e of a conditioned stimulus (CS). Three experiments monitored rabbit nictit ating (Oryctolagus cuniculus) membrane unconditioned responses to 5 intensi ties and 4 durations of periorbital electrical stimulation before and after CS or US manipulation. CRM occurred after 12 days of CS-US pairings but no t following unpaired CS/US presentations or restraint. CRM survived CS-alon e and CS/US-unpaired extinction of the conditioned response (CR) but not pr esentations of the US alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without elimi nating CRs. Data indicate CRM is a reliable, associative effect that is mor e than a generalized CR and may not be explained by habituation, stimulus g eneralization, contextual conditioning, or bidirectional conditioning.