Posttrial effects of presenting vs. omitting expected shock USs in the conditioned suppression procedure: Concurrent measurement of barpress suppression and freezing

Barpress suppression in a 1-min interval following CS trials was investigated using 16 rats in a conditioned suppression procedure with a two-stage design. For one group, each CS co-terminated with a brief shock US in Stage 1; then, in Stage 2, only half the CSs ended with a shock, which in turn was followed 1 min later by a second shock. For a second group, the two stages were reversed. When CSs were followed by single shocks in Stage 1, posttrial suppression weakened across trials; but when, in Stage 2, double shocks followed half the CSs, posttrial suppression grew stronger. When half the trials were followed by double shocks in Stage 1, posttrial suppression was maintained at initial levels but weakened in Stage 2 when single shocks followed each trial. In both stages, posttrial suppression was stronger on nonreinforced than on reinforced trials. Two factors were hypothesized to control posttrial suppression. First, posttrial suppression weakens with training under the single-shock procedure because post-shock temporal stimuli come to inhibit fear unless themselves paired with shock. Second, posttrial suppression is stronger on nonreinforced trials than on reinforced trials because freezing behaviors initiated during the CS are not disrupted by a US and so persist into the posttrial interval.     

Prolonged,unsignaled, inescapable shocks increase persistence in subsequent appetitive instrumental learning

In the first experiment, a prolonged period of intermittent, unsignaled shocks preceded appetitive runway acquisition, under either continuous (CRF) or partial reinforcement (PRF) and extinction. In the second experiment, the shock treatment came between CRF or PRF acquisition and extinction; and in the third experiment, the shocks intervened between appetitive CRF acquisition and shock-punishment extinction. The main finding was that compared with an unshocked control, shock facilitated acquisition in Experiment 1, and led to increased resistance to extinction and/or punishment in all experiments. In Experiment 1, the shock effect in appetitive extinction was seen mainly in the CRF group; in Experiment 2, the effect was to increase persistence in both the CRF and PRF groups; and in Experiment 3, shock treatment produced stronger resistance to punished extinction. The discussion is in terms of habituation and a general theory of persistence, and the concept of helplessness.     

Stereotype Threat and Women's Performance in Physics

Stereotype threat (ST), which involves confirming a negative stereotype about one's group, is a factor thought to contribute to the gender gap in science achievement and participation. This study involved a quasi-experiment in which 312 US high school physics students were randomly assigned, via their classroom cluster, to one of three ST conditions. The conditions included an explicit ST condition, an implicit ST condition, and a nullified condition. Results indicated that males in all three conditions performed similarly on a set of physics problems. Females in the nullified condition outperformed females in the explicit ST condition and females in the implicit and explicit conditions performed similarly. Males performed better than females in the implicit and explicit ST conditions, but male and female performance on the physics problems was not significantly different in the nullified condition. The implications of these findings for physics instruction and future research on gender differences in physics and ST in science are discussed.     

The effects of order of shock durations on helplessness in rats

Whereas rats exposed to a series of progressively decreasing shock durations show deficits in shuttle-escape performance 24 h later, the same number and intensity of shocks in the reverse (increasing) order of durations does not produce the “learned helplessness” effect (Balleine & Job, 1991). We conducted two experiments to establish the generality of this shock-duration order effect on other measures of distress and helplessness in rats. In Experiment 1, rats exposed to decreasing durations of inescapable shock showed reduced consumption of quinine-adulterated water (finickiness), whereas increasing durations produced no finickiness. By contrast, increasing shock durations produced greater conditioned fear to the shock context than did decreasing shock durations in Experiment 2. The differential effects of shock-duration order on finickiness and fear are explicated in terms of the specificity of fear conditioning during exposure to increasing versus decreasing series of shock duration orders.     

Preexposure to situational cues and shock intensity in two-way avoidance learning

Four groups of rats (n = 16) received 65 two-way avoidance learning trials. The groups differed with respect to the amount of exposure (0 or 4 h) to the situational cues of the apparatus prior to avoidance learning and the intensity of shock (.3 or 1.6 mA) during learning. Superior avoidance performance with weak as compared to strong shock was obtained in the nonpreexposed groups. This inverse relationship between avoidance performance and shock intensity, typical of two-way avoidance learning, was eliminated in the preexposed groups. Presumably, a latent inhibition effect occurred in the strong-shock group, which resulted in a retardation of the conditioning of fear to the situational cues and a consequent improvement in performance. The results are consistent with the effective reinforcement theory, which emphasizes in aversive learning the detrimental effect of large amounts of fear remaining following a response.     

Influence of duration and number of inescapable shocks on intrashock activity and subsequent interference effects

A three-phase investigation of the effects of duration and number of inescapable shocks with rats was conducted. In the first phase (shock treatment), separate groups were exposed either to 64 or 128 5-sec shocks or to 32, 64, or 128 10-sec shocks. Measures of intrashock activity were found to be lower for the groups exposed to 64 or 128 10-sec shocks than for any other group. In the second phase (Test Day 1), half of each group was tested for interference with FR 1, locomotor escape-avoidance learning at either 24 or 168 h following cessation of shock treatment, using a control procedure that was designed to equate groups for exposure to test shock. The results indicated that, relative to nonshock-treated controls, at each interval only the groups previously given 64 or 128 10-sec shocks were impaired in terms of escape frequency. However, all groups given at least 64 shocks exhibited depressed intertrial responding at the 24-h, but not the 168-h, interval. In the final phase (Test Days 2–4), the control procedure for equalizing test-shock exposure was discontinued and a pattern of interference effects was observed in terms of escape-avoidance response latency that was identical to that reported for the escape frequency in Phase 2. In general, these data were viewed as indicating that duration, but not total amount of shock, was a critical determinant of behavior during inescapable shock and of the subsequent interference effect. Both effects of duration were regarded as the product of a common associative process involving the learning of immobility tendencies to shock that served to compete with later escape-avoidance responding.     

Fear-motivated vicious-circle behavior maintained through secondary punishment

Two experiments attempted to establish vicious-circle behavior through fear motivation combined with secondary punishment. In Experiment 1, rats were trained with two CSs, a tone and a buzzer, paired with shock in different contexts. Secondary punishment based on delay and trace conditioning procedures facilitated running in fear-motivated rats, relative to four control groups. In Experiment 2, rats were given pairings of a tone CS with shock, and a buzzer CS with a drop into a water tank. Fear-motivated rats which received secondary punishment during either 33% or 100% of test trials exhibited self-punitive running relative to a nonpunished (0%) group and a backward-conditioning control group. Results indicate that “all secondary” vicious-circle behavior can be established through Pavlovian conditioning, thus supporting a conditioned fear interpretation.     

Signaling and affective functions in Pavlovian conditioning

The present study employed a Pavlovian-instrumental-transfer paradigm to investigate the role of conditioned fear in appetitive discrimination learning. Each of three Pavlovian training procedures was used to establish a conditioned fear excitor (CS+), a “neutral” CS (CSo), and a conditioned fear inhibitor (CS?). Then, the CSs were administered to rats in the three groups contingent upon the rewarded response in a difficult visual discrimination. In addition, half of each group received shock punishment for each incorrect response. Relative to CSo, CS+ facilitated performance in contrast to the usual interfering effect of conditioned suppressors; conversely, CS? retarded performance even when its reinforcing action (fear inhibition) was potentiated by punishment for the incorrect response. These results, together with other findings showing a reversed outcome when the CSs are administered for the incorrect response, indicate that Pavlovian conditioning comprises both general signaling and affective functions, the former reflecting a basic “expectancy” or nominal type of cognitive processing in the rat.     

Contextual associations in trace conditioning

Rats were given tone-footshock pairings with a 0-, 10-, or 30-sec trace interval between tone offset and shock onset. Half the rats within each trace interval were tested for their conditioned fear of the tone through a lick suppression procedure; the remaining rats were evaluated for their fear of the background or contextual cues through their avoidance of the compartment in which conditioning had occurred. Less conditioning was observed to the tone with increasing trace intervals. However, conditioned fear of the context increased with increases in the trace duration. The ability of the more predictive stimulus, the tone, to overshadow the contextual cues was determined by the tone’s temporal contiguity with the footshock. The need to incorporate temporal parameters within current theories of conditioning is discussed.     

Reward magnitude and shock variables (continuity and intensity) in shuttlebox-avoidance learning

In Experiment I, eight groups of rats (n = 20) were given shuttlebox-avoidance training. Two levels of shock (.3 and 1.6 mA) were combined factorially with two levels of reward (large and small) under both continuous and discontinuous (.75 sec on and 2.00 sec off) shock. Visual situational cues were absent after a shuttle response for the large-reward condition and present for the small-reward condition. Superior performance was obtained with weak rather than strong shock under both reward conditions and with large rather than small reward only under the weak-shock condition. Continuity of shock had no differential effect on performance. Experiment II allowed the conclusion that the reward effect was attributable to a reinforcement mechanism. The data were taken as support for the effective reinforcement theory, which emphasizes the importance in avoidance learning of fear conditioned to situational cues.     

The influence of shock during response prevention upon resistance to extinction of an avoidance response

A recent study found that avoidance extinction is equally facilitated by response prevention (blocking) whether the latter involves CS-alone or CS-shock presentations. An experiment was performed to determine whether this result was due to the use of a lengthy shock (5 sec) during response prevention. Five groups of rats were extinguished: (1) without prior blocking, (2) after blocking with CS only, (3) after blocking with a lengthy (5 sec) CS-contingent shock, (4) after blocking with a brief (.5 sec) CS-contingent shock, or (5) after blocking with a brief (.5 sec) shock only. The group blocked with the brief CS-contingent shock was substantially more resistant to extinction than the other four groups. The unblocked group and the group blocked with brief shock only required more trials to extinguish than the groups blocked with CS only or with lengthy CS-contingent shock, but did not differ from each other. The groups blocked with CS only or with lengthy CS-contingent shock also failed to differ from one another. The data support a significant role for Pavlovian conditioning processes in the effect of response prevention upon avoidance extinction.     

Interference with avoidance behavior as a function of qualitative properties of inescapable shocks

Temporal form (continuous vs. pulsating) and shock source (alternating current vs. direct current) were factorially combined to produce four shock treatments. The effects of inescapable presentations of these stimuli on subsequent avoidance response acquisition were measured in dogs (Experiment 1) and in rats (Experiment 2) and revealed an interaction of shock variables. Initially, all groups that received ac shock showed impaired performance for the pulsating and continuous shock conditions; groups that received dc continuous shock were also impaired, while those that received dc pulsating shock were not. While this pattern of interference persisted for dogs, it was transient in rats, with only the ac continuous-shock group continuing to be impaired. Mean avoidance performance were positively related to mean activity levels during inescapable shocks for the dc shock groups but not for the ac shock groups.     

Tonic immobility in chickens: Is a stimulus that signals shock more aversive than the receipt of shock?

Three experiments were conducted on the effect of shock and aversive conditioning on tonic immobility. In the first study, increasing the intensity of preinduction shock was shown to produce reliable increases in the duration of immobility. Using classical conditioning procedures in the second experiment, a significant effect of UCS intensity was obtained. In the third experiment, brief confrontation with a conditioned fear stimulus was found more effective than shock for enhancing immobility duration. The data were discussed in terms of the fear hypothesis of animal hypnosis and as supporting a more general notion that the anticipation of shock may be more aversive than the receipt of shock.     

Influence of conspecific stress odors and shock controllability on conditioned defensive burying

In Experiment 1, rats received a session of 80 inescapable tail shocks or no shocks while restrained in a tube. During tests of conditioned defensive burying 24 h later, the bedding of the chamber contained odors from either stressed or nonstressed conspecific donor rats. Following a single prod shock, subjects that had had prior shocks or that were tested with the stress odors spent significantly less time burying the prod, made smaller piles of bedding, and displayed more freezing behavior. The combination of prior shock and stress odors during later testing enhanced these effects. In Experiment 2, a yoked group of rats that was given inescapable shocks, in contrast to a group that had wheel-turn escape training and one that was restrained but not shocked, later showed significantly less burying and more freezing when tested for defensive burying with stress odors present. In both experiments the duration of burying and the heights of piles were positively correlated, and both of these measures were negatively correlated with freezing. The demonstrated capacity of unconditioned stress odors to mediate different degrees of fear, depending upon the controllability of prior shock, is related to other studies of learned helplessness, and the predominance of freezing over burying is discussed in terms of various types of defensive strategies, stimulus-control processes, and the author’s stress-coping-fear-defense (SCFD) theory.     

Factors affecting rats’ location during conditioned suppression training

If freezing underlies barpress conditioned suppression, then it seems odd that auditory cues paired with shock evoke more freezing than do visual cues, yet evoke similar suppression. Bevins and Ayres (1992) found that auditory and visual cues also evoked similar withdrawal from the bar and dipper areas and suggested that such withdrawal could explain the similar suppression. Seeking to understand that withdrawal, we found evidence in the present study that it was due either to adventitious punishment or to place-aversion learning. The cue for shock seemed to set the occasion for such learning. For example, we found that, as training progressed, rats’ tendency to leave the bar area during the cue first increased, then decreased, then increased again, reflecting, presumably, shock occurrence first inside, then outside, then inside the bar area again. Despite these changes in the rats’ location, barpress suppression remained stable, implying that leaving the bar area, though sufficient for barpress suppression, is unnecessary.     

One-trial context fear conditioning with immediate shock: The roles of transport and contextual cues

In three experiments, using a total of 120 albino rats, we assessed whether transportation cues might evoke some of the freezing (i.e., defensive immobility) that we see in a context on a day following a footshock given immediately after placement in that context. The results suggested that immediate shock could directly condition strong fear to both simulated and actual transport cues. Although conditioning to transport cues explains some of the freezing that is seen on the test day, it does not explain all of it. We also found evidence that some of the freezing is due to conditioning to permanent features of the context in which the immediate shock is given. The results support a role for transport cues in theories of context conditioning and argue against shock-processing accounts of the conditioning deficit that results from immediate shock.     

Preexposure to situational cues produces a direct relationship between two-way avoidance learning and shock intensity

In Experiment 1, four groups of subjects (n = 16 each) were exposed to the situational stimuli of a shuttlebox apparatus for 4 h. Subsequently, 200 two-way avoidance trials were administered (100/day) with either .3- or 1.6-mA shock and with either small or large reward (presence or absence of visual stimuli following the response). Avoidance performance was directly related to shock intensity on both days and to magnitude of reward on the 2nd day. In Experiment 2, four groups of subjects (n = 24 each) were given 4 h of exposure either to the situational stimuli of the shuttlebox or to a neutral box. Then, 10 two-way avoidance trials were given with 1.6-mA shock. Subsequently, subjects were allowed to escape from one of the shuttlebox compartments to an adjacent safe box. Following preexposure to situational stimuli, avoidance performance was superior whereas escape-from-fear performance was inferior. This latter finding demonstrated that less fear of situational cues was present during avoidance training in the preexposed condition. All of these results support the effective reinforcement theory, an extension of two-factor theory, which emphasizes the importance for avoidance learning of the amount of fear of situational cues present following a response.     

Training individuals to label nonverbal facial cues

In recent years, a considerable amount of research on nonverbal behavior has focused on identifying facial cues of various emotions. This study attempted to examine the effects of training individuals to accurately label facial affects of happiness, sadness, fear, anger, surprise, disgust, and neutral. The treatment period extended over three, one-hour group presentations based on Ekman and Friesen's (1975) model of training individuals to accurately label emotions from facial expressions. The posttest demonstrated that the experimental group significantly improved its ability to accurately label facial affect following the training program.     

Recovery from conditioned suppression to a partially overlapping compound stimulus

In a conditioned suppression paradigm, a partially overlapping compound stimulus signaled occurrences of electric shock. That compound CS consisted of 3 min of continuous illumination of the houselight with three discrete 5-see presentations of a tone superimposed. A .5-sec electric shock was coterminous with each tone presentation. Rats that received this treatment in early conditioning sessions showed considerable recovery from conditioned suppression to the houselight as the experiment progressed. However, the effect was not reversible, and it could not be demonstrated in rats that experienced extensive prior conditioning to the houselight alone. These results are discussed in relation to a hypothesis concerning the modulation of behavioral control exerted by elements of compound stimuli and as they relate to a recent theoretical model for Pavlovian fear conditioning.     

Pavlovian conditioning of fear based upon hormonal mediation of prior aversive experience

A series of three experiments was conducted to determine if epinephrine administered to animals given prior shock might support learning to new environmental cues paired with the epinephrine injection. Experiment 1, utilizing nonnaive rats, provided results snowing that such learning is possible. The effect, while dose-dependent, did not appear to be based on either epinephrine-induced place aversion or on sensitization. The results of Experiment 2 confirmed the basic finding when naive animals were utilized. Experiment 3 examined more carefully the potential contribution of generalized fear, impairment of extinction of fear, and nonspecific sensitization to the phenomenon. Since the findings did not support these alternative interpretations, it appears that epinephrine administration to previously stressed rats does indeed support new learning. The epinephrine-cue association may be mediated by either of two mechanisms: (1) higher order conditioning or (2) memory reactivation. The redintegrative function of epinephrine injections, in terms of modulating memory processing, is also discussed.