Blocking and unconditioned response diminution in human classical autonomic conditioning

Four experiments examined blocking and UR diminution in human SCR conditioning. In Experiment 1, CS_X was conditioned in compound with previously conditioned CS_A, in one group, or in a compound with another novel stimulus, CS_N, in an additional group. UR diminution occurred, but there was no post-compound difference in CRs in the two groups and no difference in responding to CS_X and CS_A following equal training on each, i.e., no blocking. The correlation between blocking and UR diminution was not significant. In Experiment 2, two groups received a blocking procedure, but one was tested on CS_X and one on CS_A. UR diminution occurred, but there were no post-compound CR or UR differences. There was again no within-subjects blocking effect. The correlation between blocking and UR diminution was not significant, but this correlation was significant when data from Experiments 1 and 2 were combined. In Experiment 3, a differential conditioning procedure was used, followed by reinforcement of two compounds, one with CS_A+ and one with CS_A-. One subgroup was tested on CS_A+ and CS_A- with reinforcement; another was tested without reinforcement. UR diminution occurred, and there was significant blocking, but only after two nonreinforced tests. Blocking and UR diminution were significantly correlated. In Experiment 4, four groups received compound conditioning after initial training with CS_A. The compound contained CS_X and CS_A for three groups and two novel CSs for the fourth. Ten nonreinforced test trials were run. The three blocking groups received two CS_As plus eight CS_Xs, four CS_As plus six CS_Xs, or all CS_Xs. The fourth group received ten nonblocked CS_Xs. CR magnitude to blocked CS_X was significantly smaller than to nonblocked CS_X during the last six test trials, but not initially. Blocking and UR diminution were not correlated, in disagreement with the first three studies. The results indicated that repeated nonreinforced test trials are needed for blocking to be observed in this preparation. The proposition that blocking and UR diminution are both due to reduced processing of the US received only partial support.     

Blocking and unconditioned response diminution in human classical autonomic conditioning

This paper summarizes the results of three experiments on blocking and unconditioned response diminution in human SCR conditioning. Recent theories of conditioning propose that reduced processing of the unconditioned stimulus due to conditioning results in reduced unconditioned response magnitude and in blocking of conditioning of a second conditioned stimulus when it is in compound with the previously conditioned stimulus. In these experiments, clear evidence of diminution of the unconditioned response was obtained in all three studies, but blocking was found only in the third study, which employed a within-subject design and in which the blocking was observed only after at least one extinction trial on both the blocked and nonblocked stimuli. Order of testing was not a factor in this delayed blocking effect. These results do not support the view that blocking occurs because of reduced processing of the unconditioned stimulus in the unconditioned response diminution sense.     

Information about the model's unconditioned stimulus and response in vicarious classical conditioning.

Four groups with 16 observers each participated in a differential, vicarious conditioning experiment with skin conductance responses as the dependent variable. The information available to the observer about the model's unconditioned stimulus and response was varied in a 2 X 2 factorial design. Results clearly showed that information about the model's unconditioned stimulus (a high or low dB level) was not necessary for vicarious instigation, but that information about the unconditioned response (a high or low emotional aversiveness) was necessary. Data for conditioning of responses showed almost identical patterns to those for vicarious instigation. To explain the results, a distinction between factors necessary for the development and elicitation of vicariously instigated responses was introduced, and the effectiveness of information about the model's response on the elicitation of vicariously instigated responses was considered in terms of an expansion of Bandura's social learning theory.     

The effectiveness of electric shock and foul odor as unconditioned stimuli in classical aversive conditioning

In a partial replication of an earlier study, eighty undergraduate volunteers were assigned to the eight cells of a three between- and two within-group experimental design. One factor was the nature of the UCS—faradic shock or a carefully-timed blast of pyridine vapor; the second factor was the UCS contingency—the UCS being contingent upon the CS or randomly interspersed; the third factor was the nature of the CS—all CSs were compounds of colored, flavored liquids, with the discriminable dimension being either color or taste. The two within-subjects factors were the successive presentation of either the CS+ of the CS? over trials in a standard classical conditioning format. The outcome measures were sip-size, order of preference, and semantic differential ratings. It was found that the foul odor UCS resulted in no aversive conditioning with either color or taste cues. Where shock was the UCS, color, but not taste, became aversive. While lending no direct support to cue-appropriateness concepts, the results reveal the complexity of cue utilization in human aversive conditioning.     

Acute stress impairs trace eye blink conditioning in females without altering the unconditioned response

Exposure to an acute stressor of inescapable swimming or intermittent tail shocks impairs classical eye blink conditioning 24h later in female rats. This effect is often attributed to a deficit in "learning," but since stress has been shown to induce analgesia, an alternative explanation is that stressor exposure reduces conditioning by lessening the perceived intensity of the unconditioned stimulus (US). To address this possibility we examined the amplitude of the unconditioned response (UR) during training and found that although exposure to the stressor impaired trace conditioning, there was no difference in the UR amplitude. We also found that eye blink responses to different US intensities (4-12 V) in the absence of training were unaffected by stressor exposure. Taken together, these experiments indicate that the stress-induced impairment of conditioning in females is not due to a decreased perception of US strength.     

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.     

Human classical conditioning

Recent reports of failure to obtain blocking in human galvanic skin response (GSR) conditioning, together with our own equivocal results with eyelid conditioning, have motivated us to re-examine the status of the conditioned stimulus (CS) in human conditioning studies. The issues raised by compound stimuli, by contextual cues and occasion setting stimuli, and by cross-modal transfer are considered in the light of data from our laboratories. These data include observations on the interchangeability of stimulus modalities during acquisition, the use of varying information loads embedded in occasion setting displays, the comparison of alternative blocking designs and the analysis of response topography in relation to stimulus variability. They suggested that an adequate account of the CS in human conditioning studies must recognize that it is dynamically processed and reprocessed both during and after acquisition.     

Evaluation of informational control and preparatory response factors in classical aversive conditioning

Subjects performed in a differential eyelid conditioning paradigm with either airpuff or infraorbital shock as the UCS. The trial series included interpolated UCS-alone presentations, and subjects rated UCS aversiveness on all trials. Ratings of the airpuff, but not the shock UCS, were negatively correlated with the magnitude of anticipatory eyelid CRs, as predicted by preparatory response or law-of-effect models of classical conditioning. However, subjects showed no tendency to rate signaled (CS-UCS) trials as less aversive than unsignaled (UCS-alone) trials, and showed no significant preference for the signaled ucs. These results suggest that the operation of informational control and preparatory response factors is more complex than is assumed by available theories. Also, instrumental shaping and preparatory response mechanisms may not be involved in the acquisition of CRs.     

A comparison of the effects of vicariously instigated classical conditioning and direct classical conditioning procedures

Two groups of Ss received either two or 16 paired classical conditioning trials beyond the peak CR. A third group received the same stimuli as in the 16 postpeak condition but in an unpaired and random order. The stimuli in all three groups were delivered directly to S. Subsequently, all three groups, including a fourth which was not given any prior direct classical conditioning, were exposed to vicariously instigated classical conditioning. This consisted of havingS observe someone (model) employed byE who received the same CS as was delivered during direct conditioning. The CS was paired with the feigned arm movement of the model, simulating a reaction to shock. This vicarious classical conditioning procedure when compared to direct classical conditioning resulted in smaller GSR magnitudes for both the CRs and UCRs. Previous experience with direct classical conditioning seems to have had an attenuating effect on GSR magnitude during the vicarious situation. A postexperimental questionnaire tended to support the results, and the relationship between the present study and current classical conditioning theory is discussed.     

Conditioned response-contingent delays of the unconditioned stimulus in human aversive conditioning.

Four groups of subjects were given either 0. 100, 500, or 1,000 msec delays of the unconditioned stimulus (UCS) contingent upon the occurrence of a conditioned response (CR) and were given a UCS 515 msec after conditioned stimulus (CS) onset when a CR did not occur. A fifth group received standard classical conditioning trials with an interstimulus interval of 515 msec. Overall performance decreased as CR-contingent UCS delay increased, with the classical conditioning group approximating the performance of the group receiving the 100-msec delay. The data were analyzed with the two-phase model of conditioning and the following results were obtained: The duration of Phase 1 of the model increased with contingent delay; operator limits associated with CR trials or with combined CR-CR (CR absent) trials decreased as a function of delay; and operator limits associated exclusively with CR trials were unaffected by the delay. Subjects receiving a contingent delay of 0 msec gave the shortest latency responses and exhibited reliable latency decreases across trials, suggesting an attempt to "beat" the UCS. The results were interpreted as contrary to what would be expected from low-of-effect theories which postulate that reinforcement results from a CR-UCS interaction, although they could be subsumed under a drive or an associative strength theory in which the aversive, or CR-supportive, strength of the UCS is assumed to be negatively correlated with contingent UCS delay.     

Conditioning the unconditioned response: modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to an unconditioned stimulus (US) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit nictitating (Oryctolagus cuniculus) membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or US manipulation. CRM occurred after 12 days of CS-US pairings but not following unpaired CS/US presentations or restraint. CRM survived CS-alone and CS/US-unpaired extinction of the conditioned response (CR) but not presentations of the US alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning.     

Salivary conditioning with antennal gustatory unconditioned stimulus in an insect

Classical conditioning of olfactory conditioning stimulus (CS) with gustatory unconditioned stimulus (US) in insects has been used as a pertinent model for elucidation of neural mechanisms underlying learning and memory. However, a conditioning system in which stable intracellular recordings from brain neurons are feasibly obtained while monitoring the conditioning effect has remained to be established. Recently, we found classical conditioning of salivation in cockroaches Periplaneta americana, in which an odor was associated with sucrose solution applied to the mouth, and this conditioning could be monitored by activities of salivary neurons. Application of gustatory US to the mouth, however, leads to feeding movement accompanying a movement of the brain that prevents stable recordings from brain neurons. Here we investigated whether a gustatory stimulus presented to an antenna could serve as an effective US for producing salivary conditioning. Presentation of sucrose or sodium chloride solution to an antenna induced salivation and also increased activities of salivary neurons. A single pairing trial of an odor with antennal presentation of sucrose or sodium chloride solution produced conditioning of salivation or of activities of salivary neurons. Five pairing trials led to a conditioning effect that lasted for one day. Water or tactile stimulus presented to an antenna was not effective for producing conditioning. The results demonstrate that gustatory US presented to an antenna is as effective as that presented to the mouth for producing salivary conditioning. This conditioning system provides a useful model for studying the neural basis of learning at the level of singly identifiable neurons.     

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.     

A minicomputer program for the resolution of response frequency and latency in classical conditioning preparations

This classical conditioning program is capable of controlling stimulus events and recording response data in experiments using the rabbit’s nictitating membrane and/or iaw-movement responses. The main features of the program, implemented on the PDP·12 computer, are the ability to resolve response latency within a 1 msec error range and to display the response topography on the computer’s cathode ray tube. The extreme accuracy in latency measurement cannot be duplicated either by conventional hand-scoring methods involving oscillographic records or by other minicomputer conditioning programs.