The effects of interpolated US alone (USa) presentations on classical nictitating membrane conditioning in rabbit(Oryctolagus cuniculus)

The nictitating membrane (NM) response of 36 rabbits was classically conditioned using a 1,000-Hz tone (CS) paired with circumorbital shock (US) at a 250-msec CS-US interval. Two experimental groups received additional presentations of the US given alone (USa), either 30 seconds (Group E30) or 60 seconds (Group E60) following each CS-US pairing, and their performance was compared to that of control Ss (Group C60) which never experienced USa. Presentations of USa resulted in significant and approximately equal performance decrements in both experimental groups relative to the C60 controls. However, no significant differences among the groups appeared during an extinction phase. The effects of USa presentations were discussed in terms of Papsdorf’s consolidation interpretation and Rescorla’s (1967) contingency theory of conditioning, and appeared to favor the latter view. Additional analyses led to the conclusions that (1) the increased amplitude of the NM UR on paired CS-US trials relative to USa trials can be attributed, at least in part, to the simple laws of the reflex, independent of the conditioning processper se, and (2) the partial reinforcement extinction effects previously reported by Leonard and Theios (1968) cannot be attributed solely to the presence of USa in their continuous reinforcement control Ss.