UCL Logo

E. James Kehoe
School of Psychology, The University of New South Wales, Sydney, Australia


Monday 27 June 2005



Seminar Room B10 (Basement)

Alexandra House, 17 Queen Square, London, WC1N 3AR



Temporally-Specific Extinction and Real-Time Processes


Since Pavlov, extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US), mostly commonly by its removal.  This research, however, reveals that extinction of the rabbit nictitating membrane (NM) response occurs even when the CS is still paired with the US.  In three experiments, rabbits were initially trained with a 1400-ms CS that was paired with the US using a mixture of two ISIs, 200 ms and 1200 ms.  The resulting CRs showed double peaks, one timed for each of the ISIs.  Training was then shifted to just one of the ISIs. Consequently, the CR peak based on the absent ISI showed the hallmarks of extinction, specifically, a progressive decline across sessions and spontaneous recovery between sessions.  When the absent ISI was reintroduced, there was evidence of savings, particularly rapid reacquisition of the extinguished CR peak.  Throughout all these manipulations, overall CR likelihood to the entire CS remained high. These results support real-time models of NM conditioning that temporally segment the CS into microstimuli, each capable of acquiring excitation and/or inhibition according to its temporal distance from the US.  Conversely, these results challenge theories of extinction rely on contextual control, US representations, CS processing, and/or habituation.