No abstract

Two experiments with rabbits showed that the differential modulation of a conditioned eyeblink response (CR) by 30-s auditory stimuli previously paired with shock was independent of the locus of shock application. In Experiment 1, the modulation occurred when the CR was trained with paraorbital shock and the 30-s stimuli were trained with either hindleg or paraorbital shock. Experiment 2 replicated the observed adequacy of hindleg shock for modulation training, under 2 different conditions of eyeblink conditioning. The data, along with the findings that the same 30-s stimuli similarly facilitate the unconditioned eyeblink and the airpuff-elicited startle response (Brandon, Bombace, Falls & Wagner, 1991), were viewed as supporting the notion that the CR-modulation is dependent upon a conditioned fear response elicited by the 30-s cues (Wagner & Brandon, 1989).

Two experiments are reported that use rats in a conditioned suppression situation. The experiments, designed to remove confounds that have complicated interpretations of prior research, tested the context-blocking hypothesis, the proposition that static apparatus cues or conditioning contexts can block conditioning to discrete conditioned stimuli (CSs). Experiment 1, like previous work, tested for conditioning to the target CS in the same context that had been preconditioned and in which target conditioning had occurred; the experiment demonstrated a context-blocking like effect. Experiment 2 tested for conditioning not only in the preconditioned context but also in a nonpreconditioned context. Evidence for context blocking appeared similar in the two test situations. This suggests that conditioned contexts block the acquisition of associative strength by discrete CSs at the time of target conditioning (e.g., Rescorla & Wagner, 1972) and not through performance factors at the time of testing (e.g., Gibbon & Balsam, 1981).

In four experiments using the conditioned suppression procedure with rats, we compared the effects of extending conditioned stimuli (CSs) before versus after reinforcement (called B vs. A extensions). In Experiments I and 2, Group 0 (no extension) received 2-min noise CS trials (3 per day in Experiment 1, 1 per day in Experiment 2) that terminated with a 1-s grid shock unconditioned stimulus (US). For Group B, the CS began 12 min before the US; for Group A, the CS began 2 min before the US but persisted for 10 min past US termination. In Experiments 3 and 4, similar trials (3 per day in Experiment 3, 1 per day in Experiment 4) included a 2-min light CS that always terminated with the US; thus the noise CS became a systematically manipulated context cue in which lightshock pairings were embedded. In Experiments 1 and 2 we found asymmetrical effects of CS extensions: B extensions weakened conditioning more than did A extensions. In Experiments 3 and 4 we found symmetrical effects: A and B extensions weakened context conditioning equally. A realtime model of conditioning that combined the Frey-Sears (1978) dynamic attention rule with the Rescorla-Wagner (1972) model anticipated the asymmetrical effects preasymptotically and the symmetrical effects at asymptote. John W. Moore for his support throughout the project.

Two experiments with rabbits showed that the differential modulation of a conditioned eyeblink response (CR) by 30-s auditory stimuli previously paired with shock was independent of the locus of shock application. In Experiment 1, the modulation occurred when the CR was trained with paraorbital shock and the 30-s stimuli were trained with either hindleg or paraorbital shock. Experiment 2 replicated the observed adequacy of hindleg shock for modulation training, under 2 different conditions of eyeblink conditioning. The data, along with the findings that the same 30-s stimuli similarly facilitate the unconditioned eyeblink and the airpuff-elicited startle response (Brandon, Bombace, Falls, & Wagner, 1991), were viewed as supporting the notion that the CRmodulation is dependent upon a conditioned fear response elicited by the 30-s cues (Wagner & Brandon, 1989). demonstrated what they referred to as the differential modulation of a conditioned eyeblink response (CR) by contextlike Pavlovian stimuli. The contextual stimuli were two 30-s auditory stimuli (designated A and B) that were trained under the arrangement that a single, 4-mA, 50-ms, paraorbital shock consistently occurred between 8 and 28 s after the onset of A, but never occurred in the presence of B. When a 1,050-ms target conditioned stimulus (CS) that had been separately pretrained to elicit an and Wagner (1991) studies that eyeblink tendencies were conditioned to the contextual stimuli and that although these were below some response threshold, so as not to be evidenced in responding to the contextual stimuli in isolation, they may nonetheless have been adequate to increase the amplitude of an eyeblink CR otherwise elicited.There are two related predictions concerning the generality of the CR modulation effect reported by Brandon and Wagner (1991) that follow from the view that the results represent the action of a conditioned emotional response. One is that contextual cues, as trained with paraorbital shock by , should modulate a range of other defensive behaviors besides the eyeblink CR. This prediction was supported by Brandon, Bombace, Falls, and Wagner (1991), who showed that the same contextual cues that modulated the eyeblink CR similarly modulated the eyeblink unconditioned response (UR) and the airpuff-elicited startle response. The second prediction, which is the focus of the present study, is that these stimuli should become effective in modulating the eyeblink CR by being paired with any of a range of aversive USs that should be equally capable of supporting the acquisition of a conditioned emotional response. That is, the eyeblink modulation otherwise observed by Brandon and Wagner and by should not be unique to contextual stimuli trained with paraorbital shock.This prediction was tested in the two experiments reported here. Both assessed the possibility that hindleg shock would be adequate to condition contextual stimuli that could subsequently modulate the amplitude of the eyeblink CR to a CS independently paired with a paraorbital US. E...