CONTEXTUALLY BASED CONDITIONAL DISCRIMINATION OF THE RABBIT EYEBLINK RESPONSE

Rabbits received conditional discrimination training using contextual stimuli to set the occasion for stimulus pairings during eyelid condit ioning. Specifically, animals were exposed to either the presence or t he absence of an oscillating chamber light throughout the intertrial i nterval (50 +/- 10 s). For half the animals, this light signaled paire d presentations of a discrete tone conditioned stimulus (CS) and air p uff unconditioned stimulus (US) while darkness signaled presentations of only the tone CS. The remaining animals experienced the opposite co ntextual relationship to the conditioning stimuli. These trial types o ccurred pseudo-randomly across a session, with all transitions between contextual settings (i.e., light or dark) taking place immediately at the CS-US offset. Under these conditions, animals successfully utiliz ed the contextual stimuli as conditional cues for differential respond ing to the shared CS. Moreover, both light and dark were equally effec tive as discriminative stimuli. A subset of animals received further t raining in which the contextual contingency was removed by restricting all conditioning to the CS-alone context. Without the contingency in place, subsequent CS presentations (paired and CS-alone) evoked equiva lent conditioned responding across three sessions of training. Followi ng the reinstatement of the contextual contingencies, discriminatory r esponding was immediately observed and returned to previous levels wit hin three sessions. Finally, animals appeared to use the static repres entation of the conditional cue, rather than the phasic transition bet ween cues, for discriminatory responding. These findings are discussed in terms of current neurobiological models of eyelid conditioning. (C ) 1998 Academic Press.