The CS-US interval function in rabbit nictitating membrane response conditioning: Single vs multiple trials per conditioning session

The effect of varying trials per day conditions on the CS-US interval or interstimulus interval (ISI) function in rabbit nictitating membrane response conditioning was studied in two experiments. Experiment 1 showed that a 1250-msec ISI was more effective than a 250-msec ISI when there was 1 trial/day. Experiment 2 showed that as the number of trials per day decreased from 20 to 1, the superiority of the 250-msec ISI group over the 1250-msec ISI group declined, with a reversal at 1 trial/day. Results are interpreted in terms of the role of a hypothesized CS-elicited short-duration orienting response in CR performance.     

Repeated acquisitions and extinctions in classical conditioning of the rabbit nictitating membrane response

The rabbit nictitating membrane (NM) response underwent successive stages of acquisition and extinction training in both delay (Experiment 1) and trace (Experiment 2) classical conditioning. In both cases, successive acquisitions became progressively faster, although the largest, most reliable acceleration occurred between the first and second acquisition. Successive extinctions were similar in rate. The results challenge contextual control theories of extinction but are consistent with attentional and layered-network models. The results are discussed with respect to their implications for the interaction between cerebellar and forebrain pathways for eyeblink conditioning.     

The role of CS-US contiguity in classical conditioning of the rabbit's nictitating membrane response to serial stimuli

The rabbit's nictitating membrane response was classically conditioned to a serial tone-light compound (CS1-CS2), in which the CS1-CS2 and CS2-US intervals were each manipulated over the values of 200, 400, 800, and 1600 msec in a between-groups, factorial design. In addition, at each level of the CS2-US interval, there was a control group that received CS2 and the US. Within the serial compound, the CS2 was found to be highly efficacious in that the CS2-US interval determined the rate of CR acquisition to the compound as a whole and to CS2 in particular. Moreover, CR probability during CS2 largely overlapped the performance of the corresponding single-stimulus controls. Outside the context of the compound, CR frequency on CS2 test trials fell below control levels at the 200- and 400-msec CS2-US intervals. The results can be interpreted as indicating that a generalization decrement or information loss occurred in transferring from compound training to CS2 testing. In addition, the theories of Rescorla and Wagner (In A. Black & W. F. Prokasy, Eds., Classical conditioning II, New York: Appleton-Century-Crofts, 1972) and Mackintosh (Psychological Review, 1975, 82, 276–298) may be extended to account for the present results.     

Unconditional-stimulus locus and interstimulus-interval shift in rabbit(Oryctolagus cuniculus) nictitating membrane conditioning

The nictitating membrane response of rabbits was conditioned at a 200 msec interstimulus interval (ISI) with either circumorbital (C) or paraorbital (P) shock as the unconditional-stimulus locus. After 3 acquisition days half of each group was shifted to a 700 msec interstimulus interval. Results indicated: (1) more rapid acquisition for Group C, (2) postshift response decrements for both groups, (3) more rapid and stable, as well as complete return to preshift performance levels for Group C. Results were discussed in terms of the response-shaping hypothesis and the contiguity-substitution hypothesis in explaining both conditional response emergence and subsequent modifications of CR topography.     

Double responding in classical nictitating membrane conditioning with single-CS dual-ISI training

Rabbits were classically conditioned under a single-CS dual-ISI paradigm. Contrary to a previous experiment by Frey (1970), a separate CR was conditioned at each interstimulus interval (ISI), producing a double response (DR) on long-ISI trials. Further experiments indicated that DR development is facilitated by (a) circumorbital US-location and (b) relatively high US-intensity. However, subsequent shifts to nonoptimal conditions did not produce substantial decreases in DR frequency. The presence of DRs appears to be readily amenable to interpretation in terms of a Pavlovian stimulus-trace mechanism in which the US becomes associated with a particular temporal portion of the CS. An instrumental-response-shaping hypothesis of classical conditioning can explain these data only if the hypothetical reinforcement mechanism is assumed to be considerably more complex than had previously been supposed.     

Effect of preacquisition UCS exposure on classical conditioning of the rabbit's nictitating membrane response

Conditioning of the rabbit nictitating membrane response was found to be inversely related to the number (0, 50, 200, 350) and intensity, (0, 1, 3, 5 mA) of preacquisition UCS exposures and directly related to the interval between preexposure and acquisition (0 or 24 hr). The results were discussed in terms of sensory adaptation, habituation, blocking, and emotional reactivity.     

Classical conditioning of the rabbit's nictitating membrane response under fixed and mixed CS-US intervals

The rabbit's nictitating membrane response was classically conditioned to a tone CS, followed by an electric shock US, at two randomly alternating CS-US interstimulus intervals (ISIs). Different groups were exposed to different proportions of 200- and 700-msec ISIs. The study revealed: (a) CR percentage was a direct function of the proportion of 200-msec ISIs; (b) trials to the first test-trial CR were an inverse function of the proportion of 200-msec ISIs; (c) CR onset latencies decreased over training; (d) CR peak latencies coincided with the temporal loci of the US; and (e) groups exposed to both ISIs acquired double-peaked CRs. Moreover, the amplitudes of nictitating membrane responses in the present experiment paralleled certain quantitative aspects of the free operant key peck response rates of pigeons trained under two mixed inter-reinforcement intervals. The results were discussed with respect to the micromolar response shaping and macromolecular CS-trace accounts of classical conditioning.     

CS Intensity effects on rabbit nictitating membrane conditioning,extinction and generalization

One purpose of the present experiments was to determine if the Grice and Hunter (1964) observation of augmented within-versus between-Ss CS intensity effects in human eyelid conditioning would be obtained in conditioning of the rabbit’s nictitating membrane response under two (Experiment 1) and four (Experiment 2) CS intensity values. In addition, a determination was made of the effects of CS intensity upon extinction and stimulus intensity generalization gradients. The studies revealed that: (a) while acquisition performance was positively related to CS intensity, the effect was independent of the between and within-S manipulation of CS intensity; (b) rate of response decrement in extinction was an inverse function of CS intensity; and (c) a positively sloped intensity generalization gradient was obtained when the training stimulus was the low-intensity one. Overall, these results are most consistent with Hull’s (1949) stimulus intensity dynamism account of CS intensity effects in conditioning.     

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.     

Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Neuronal unit activity was recorded from the abducens (6th nerve) nucleus, the "final common path," during classical conditioning of the nictitating membrane (NM) response in the rabbit, with the use of a tone conditioned stimulus, an air puff unconditioned stimulus (UCS), 250-msec interstimulus interval, and 60-sec intertrial interval. Animals were given 2 days of conditioning training (104 trials in eight blocks per day) and 1 day of extinction. Control animals were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units--"multiple unit" recording--was compared with the amplitude-time course of the NM response. Between-blocks comparisons of neural and behavioral responses indicated an essentially perfect correlation during acquisition of the conditioned response (Day 1, r = .99; Day 2, r = .98) and a slightly lower correlation during extinction (r = .93) for the conditioning animals. Within-blocks comparisons indicated a close correspondence between the histograms of unit activity and the amplitude-time course of the NM response for the conditioning animals in all phase of training and for the control animals in the UCS trial blocks.     

Temporal discrimination using different feature--target intervals in classical conditioning of the rabbit's nictitating membrane response

In a typical conditional discrimination, a target stimulus (X) is reinforced during one feature cue (A-->X+), but not during another feature cue (B-->X-). The present experiments used only a single "feature" cue (a 66-sec tone). On half of the trials, the target stimulus (a 400-msec light) was paired with the reinforcer when the feature-target interval was one duration (e.g., 5 sec). On the remaining trials, the interval was different (e.g., 45 sec), and the target stimulus was presented without the reinforcer. All the animals acquired this temporal discrimination, and subsequent testing with other feature-target intervals yielded generalization-like gradients. These results provide solid evidence that each portion of a feature cue is encoded in a distinctive fashion. Had temporal encoding not occurred, the feature cue would have been just as ambiguous a predictor of the reinforcer as was the target stimulus, and discrimination would not have been possible. The integration of real-time temporal encoding mechanisms into models of conditional discrimination is discussed.     

The effects of overtraining and successive extinctions upon nictitating membrane conditioning in the rabbit

In Expt. I Group SAE (N = 16) received four successive acquisitions and extinctions of a classically conditioned nictitating membrane response while Group OTC (N = 8) received an equivalent amount of acquisition training followed by a single extinction session. Successive extinctions resulted in a decrease in resistance to extinction (Rn), but extended acquisition training had no significant effect. In Expt. II a total of 96 subjects participated in a factorial study of the effects of various amounts of overtraining at two different UCS intensities. When CR amplitude was asymptotic extended training had no significant effect upon Rn; when amplitude was below asymptote Rn was correspondingly reduced.