Habituation to shock and learned persistence in preweanling, juvenile, and adult rats.

In Exp I, a prolonged shock-habituation treatment given between runway acquisition and simple extinction promoted persistence in both preweanling and juvenile Holtzman rats. Exp II showed even stronger persistence effects in a punished-extinction test given after shock treatment, the effects being stronger in preweanlings than in juveniles. Exp III demonstrated that shock treatment at infant-to-preweanling age resulted in increased persistence that survived a 42-day retention interval in a nonreward extinction test. Exp IV demonstrated habituation to shock in preweanlings and juveniles in terms of recovery of suppression of milk intake in the shock situation and, compared with controls, in terms of reduced latency to eat in a punished-reward test at several retention intervals. Exp V showed that the strength of persistence to approach in a runway reflected the presumed degree of habituation in 70-day-old Ss. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of Pavlovian conditioning with a zero operant contingency: Chronic exposure to signaled inescapable shock maintains learned helplessness effects.

Four studies, with 372 male Holtzman rats, examined the effect of Pavlovian contingencies and a zero operant contingency (i.e., uncontrollability) on subsequent shock-escape acquisition in the shuttle box using triads consisting of escapable-shock (ES), yoked inescapable-shock (IS), and no-shock (NS) rats. After exposure to 50 signals and shocks per session for 9 sessions, interference with shuttlebox escape acquisition for IS Ss was a monotonically increasing function of the percentage of signal–shock pairings during training (Exp I), with 50% pairings producing little or no impairment. Without regard to signaling, ES Ss performed as well as NS Ss. Exp II demonstrated that training and test conditions led to substantial and equal impairment in IS Ss preexposed for 1 session to 100 or 50% signal–shock pairings or to unsignaled shocks. In Exp III, chronic exposure to 100% signaled ISs resulted in impairment only if the signal (light) was present during the shuttlebox test. The continuous presence of the signal during the test contrasted with its discrete (5-sec) presentation during training and suggested that an antagonistic physiological reaction rather than a specific competing motor response had been conditioned. Exp IV provided evidence for possible conditioned opioid mediation. Findings suggest that chronic exposure to uncontrollable shocks maintains the impairment produced by acute exposure only if the shocks are adequately signaled. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure to learn to escape by rats previously exposed to inescapable shock is partly produced by associative interference.

2 experiments demonstrated that the effects of prior exposure to inescapable shock on the subsequent acquisition of an escape response in rats is determined by the nature of the contingency that exists between responding and shock termination during the escape learning task, and not by the amount of effort required to make the response or the amount of shock that the S is forced to receive during each trial. Exp I, using 48 male Simonsen rats, showed that inescapably shocked Ss did not learn to escape shock in a shuttle box if 2 crossings of the shuttle box were required (fixed ratio, FR, -2) to terminate shock, but did learn this FR-2 response if a brief interruption of shock occurs after the 1st crossing of the FR-2. Exp II with 72 Ss showed that inescapably shocked Ss learned a single-crossing escape response as rapidly as did controls, but were severely retarded if a brief delay in shock termination was arranged to follow the response. Results are discussed in terms of the learned helplessness hypothesis, which assumes that prior exposure to inescapable shock results in associative interference. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In search of reliable persuasion effects: II. Associative interference and persistence of persuasion in a message-dense environment.

Conducted 3 experiments, with a total of 272 Ss, to test an associative learning model. Fictitious consumer-product brands were used as stimuli and brand evaluations as responses. In each experiment, Ss received messages concerning up to 54 brands drawn from up to 12 product categories. Exp I demonstrated associative interference—messages advocating diverse evaluations of similar products led to rapid decay of persuasion. Exp II demonstrated reduction of associative interference—messages advocating similar evaluative responses to similar products facilitated associative learning and attenuated decay of persuasion. Exp III demonstrated the correlation between learning of brand-evaluation associations and persuasion. Results suggest that associative learning theory can provide a useful tool for analyzing the persisting impacts of persuasive messages in message-dense environments. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned helplessness and immunization: Sensitivity to response–reinforcer independence in immunized rats.

Exps I and II, with 62 male Holtzman rats, examined the learned helplessness and immunization effects using a test in which appetitive responding was extinguished by delivering noncontingent reinforcers. Contrary to learned helplessness theory, "immunized" Ss showed performance virtually identical to that of Ss exposed only to inescapable shock and different from that of nonshock controls. Exp II suggested that the helplessness effect and the lack of immunization were not due to direct response suppression resulting from shock. In Exp III, in which the immunization effect was assessed in 28 Ss by measuring the acquisition of a response to obtain food when there was a positive response–reinforcer contingency, immunization was observed. Results cannot be explained on the basis of proactive interference and instead suggest that Ss exposed to the immunization procedure acquired an expectancy of response–reinforcer independence during inescapable shock. Thus, immunization effects may reflect the differential expression of expectancies rather than their differential acquisition as learned helplessness theory postulates. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of naltrexone and signaling inescapable electric shock on nociception and gastric lesions in rats.

Two experiments, with 144 male Long-Evans hooded rats, examined the antinociceptive effects of signaled shock and its physiological underpinnings. In Exp I, Ss were exposed to 1 of 3 shock conditions: no shock, unsignaled shock, and signaled (by a 10-sec, 1,000-Hz tone) shock. In each condition, Ss were tested hourly in the absence of tones for nociception, with vocalization to shock used as the behavioral measure. Ss receiving signaled shocks had stomach ulcer scores intermediate between those of no-shock and unsignaled shock Ss. Signaled-shock Ss also displayed a pronounced vocalization antinociception effect. This suggested that signaled shock may be less aversive. Exp II investigated a possible role of endogenous opiate peptides in these effects. Ss received hourly injections of either the opiate antagonist naltrexone (7 mg/kg, ip) or saline. There were no significant effects of naltrexone on either stomach pathology or nociception scores. The same effects of signaled shock were obtained as in Exp I. It is concluded that the role of endogenous opiates in the effects of signaled shock seen here is minimal. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: A tool for the neural analysis of taste-visceral associations.

Investigated the ability of animals to form taste aversions following neural manipulations. In Exp 1, 10 rats received intraoral infusions of sucrose every 5 min starting immediately after the injection of LiCl. 12 controls were injected with NaCl. Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected Ss decreased their ingestive taste reactivity over time; aversive behavior increased. Controls maintained high levels of ingestive responding and demonstrated virtually no aversive behavior following sodium injection. Ss were tested several days later for a conditioned taste aversion (CTA). Rats previously injected with lithium demonstrated significantly more aversive behavior than controls. Exp 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, difference in the ingestive behavior was observed. In Exp 2, naive rats were injected with NaCl or LiCl but did not receive their 1st sucrose infusion for 20 min. Ss also received infusions at 25 and 30 min postinjection. There were no differences in the task reactivity behavior displayed. Rats dramatically changed their oromotor responses to sucrose during the period following LiCl administration, provided the infusions started immediately after injection, a change attributable to associative processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory preconditioning in rats following early visual deprivation.

Conducted 3 experiments in which a total of 131 light- and dark-reared (LR and DR) male hooded rats were given sensory preconditioning (SPC). In each experiment, Ss were presented with 2 stimuli either paired or unpaired, followed by conditioning to 1 and extinction on the other. 2 auditory stimuli were used in Exp. I. SPC was found for both LR and DR Ss, with no significant difference due to rearing condition either in acquisition or in the SPC test. In Exp. II, light and tone were employed; SPC was demonstrated and was more effective for LR than DR Ss. In Exp. III, rectangle stimuli were employed. The effect of SPC was evidenced in LR Ss; however, performance of DR Ss was not significantly different from that of controls. Results are discussed in terms of the effect of early visual deprivation on information-processing mechanisms. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Uncontrollable shock proactively increases sensitivity to response-reinforcer independence in rats.

Learned helplessness theory predicts that animals exposed to inescapable shock acquire an expectancy of response-reinforcer independence, which proactively interferes with learning of response-reinforcer dependence. The theory also predicts that this expectancy can increase sensitivity to subsequent instances of response-reinforcer independence. Two experiments, with 42 male Holtzman rats, tested the latter prediction in a paradigm that minimized the confounding effects of shock-induced activity deficits. In Exp I, Ss were trained to respond for food, then given either escapable, inescapable, or no shock. Subsequently, they received 2 sessions of response-contingent food followed by sessions of noncontingent food deliveries. During this phase, inescapably shocked Ss decreased responding faster than did controls. Exp II replicated this finding with a different schedule of food delivery and a procedure that more directly minimized the possibility that the outcome was due to either direct or indirect shock-induced activity changes. Results support the prediction that uncontrollable aversive events can increase an animal's sensitivity to noncontingent response-reinforcer relationships. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic differences in avoidance learning by Rattus norvegicus: Escape/avoidance responding, sensitivity to electric shock, discrimination learning, and open-field behavior.

Studied the behaviors of Long-Evans rats selectively bred for either good (SHA line) or poor (SLA line) shuttle box avoidance learning. The results of Exp I indicated that the phenotypic difference in avoidance learning was not associated with differences in speed of escape or avoidance responding. Differences between the lines in frequency of intertrial responses (ITRs), which appeared during training but not during pretest, suggest that ITRs in Ss of the low-avoidance SLA line were more suppressed by electric shock than in Ss of the high-avoidance SHA line. This result suggests that SLA Ss may be more emotionally responsive than SHA Ss. Exp II demonstrated that the Ss of the 2 lines did not differ in absolute sensitivity to electric shock, and Exp III showed that the poor performance of the SLA line was not due to an inability to learn. Ss also provided evidence that the poor avoidance learning by SLA Ss was due to their emotional reactivity. Observations of open-field behavior in Exp IV were consistent with this hypothesis. It is concluded that the major consistent correlate of the phenotypic difference in avoidance learning was greater emotionality or emotional reactivity in SLA than in SHA Ss. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of response restriction during exposure to inescapable shock upon subsequent one-way and shuttle-avoidance performance in rats.

Investigated the effects of signaled inescapable shock on subsequent avoidance performance in 3 experiments with male Holtzman rats (N = 188). Exp I indicated that prior shock exposure (PSE) facilitated 1-way and shuttle avoidance. When Ss were preshocked in a harness so that free mobility was not possible, the facilitative effects of PSE on shuttle, but not 1-way avoidance performance, were largely reduced. Exp II indicated that activity during CS periods following PSE was greater among unrestrained than restrained Ss. Exp III showed that immobilization via injection of succinylcholine chloride did not affect the facilitative effects of PSE relative to that of Ss preshocked in a harness. Results are interpreted in terms of response repertoire changes produced by PSE in conjunction with the response requirement of the avoidance task. (French summary) (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monitoring eye movements under conditions of associative matching, response production, and stimulus and response production.

Monitored eye movements in each of 3 studies with 20, 19, and 18 undergraduates, respectively, while Ss were given 8 study trials on a 7-item paired-associate list. Ss were then subjected to a single test trial of associative matching (Exp. I), response production (Exp. III) or stimulus and response production (Exp. IV). A 4th study with 42 Ss, (Exp. II), without eye movement monitoring, involved 3 groups of Ss given either 2, 4, or 6 study trials followed by a single test trial of associative matching. Results, with the exception of Exp. I, were generally consistent with a 2-stage notion of verbal paired-associate learning. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of avoidance in aggressive responses to attack and no attack.

In 2 experiments male Ss interacted with a presumed opponent in a task that permitted the 2 participants to exchange various intensities of shock, including a zero intensity. The Ss' responses were considered separately following attack (receipt of shock) and no attack (no receipt of shock). For responses following no attack, the Ss' aggressive behavior varied with their ability to avoid further shock. Relative to controls, Ss who could avoid further shock by nonaggression (Exp I, 40 college students) were less aggressive. Those who could avoid shock by being very aggressive (Exp II, 20 college students) were more aggressive than controls. Aggressive responses following attack, however, were not influenced by avoidance contingencies. The ability to avoid further shocks apparently influenced males' aggressive responses in the absence of attack but failed to influence males' aggressive responses to attack. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual sampling after lesions of the superior colliculus in rats.

In 2 experiments with 20 male black-hooded rats, Ss with bilateral lesions of the superior colliculus showed significantly poorer relearning of a horizontal/vertical stripe discrimination than control Ss. In Exp I, all Ss showed disruption of performance when a stimulus–response (S–R) separation was introduced by raising the stimuli above the site of responding. However, colliculectomized Ss were much more disturbed by the S–R separation than were control Ss. In Exp II, all Ss showed lower performance levels when conflicting patterns were introduced into the upper portion of the stimulus doors, but this time Ss with collicular lesions were less disturbed than controls. It is suggested (a) that when the stimulus and response sites are discontinuous, rats must make an appropriate orienting response to effectively sample the visual stimuli and (b) that lesions of the superior colliculus alter performance by interfering with this orienting behavior. The impairment in relearning is attributed to the absence of preoperative overtraining on the discrimination task. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of UCS preexposure on excitatory and inhibitory rabbit eyelid conditioning: An associative effect of conditioned contextual stimuli.

Preconditioning experience with the UCS retards subsequent excitatory conditioning. Three experiments demonstrated that the UCS retardation effect is attenuated by associative manipulations of contextual stimuli of the UCS preexposure environment. The UCS retardation effect was reduced by (a) altering contextual stimuli between preexposure and conditioning (Exp I, 49 New Zealand male rabbits; Exp II, 28 Ss); and (b) latently inhibiting contextual stimuli subsequent to UCS (Exp III, 36 Ss). Although UCS preexposure retarded excitatory conditioning, results of Exp IV (48 Ss) demonstrated that UCS preexposure facilitated inhibitory conditioning. Overall findings indicate that an association between contextual stimuli and preexposed UCS contributes to the effects of preconditioning UCS experience on subsequent learning. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Malleability of conditioned associations: Path dependence.

Using conditioned suppression of barpressing to investigate the stability of a conditioned stimulus–unconditioned stimulus (CS–UCS) association, the present authors gave 151 water-deprived rats either a few pairings of the CS with a strong footshock UCS or many pairings with a weak footshock UCS so that barpress suppression in response to CS was equated. Exp I established training parameters that yielded this equivalence. Specifically, rapid acquisition to a preasymptotic level of responding with strong shock produced suppression comparable to the asymptotic level reached more slowly with weak shock. Exp II showed that although equivalent performance was obtained from extensive conditioning with a weak shock or limited conditioning with a strong shock, only extensive conditioning with weak shock resulted in retarded acquisition of an association between that same CS and a footshock level perceived as midway between the 2 initial training shock intensities as implied by asymptotic performance in Exp I. Exp III demonstrated that the observed retardation in Ss given many conditioning trials with weak shock was CS-specific. It is concluded that the malleability of learned behavior is not simply a function of initial associative strength but is dependent on the path during initial acquisition. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the amygdala, but not of the cerebellum or red nucleus, block conditioned fear as measured with the potentiated startle paradigm.

In Exp I, 97 male Sprague-Dawley albino rats were given 10 light–shock pairings on 2 successive days. At 24–48 hrs following training, groups of Ss received bilateral transection of the cerebellar peduncles, bilateral lesions of the red nucleus (which receives most of the cerebellar efferents), or bilateral lesions of the central nucleus of the amygdala. Controls were sham operated. At 3–4 days after surgery, Ss were tested for potentiated startle (PS [increased acoustic startle in the presence of the light previously paired with shock]). PS was blocked by lesions of the central nucleus of the amygdala but not by transection of the cerebellar peduncles or lesions of the red nucleus. Exp II, in which a visual prepulse test was used with 14 Ss, indicated that the blockade of PS observed in Ss with amygdala lesions could not be attributed to optic tract damage. Exp III, with 20 Ss, demonstrated that the absence of potentiation in Ss with amygdala lesions was not simply due to a lowered startle level ceiling, because these Ss could show increased startle with increased stimulus intensity and with administration of intraperitoneal strychnine, (0.75 mg/kg), a drug that increases startle. Results are consistent with the hypothesis that the amygdala is involved in fear conditioning. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus selection and irrelevant stimuli in discrimination learning by pigeons.

Studied discrimination learning in 2 experiments with 32 and 16 White Carneaux pigeons. Exp. I confirmed that Ss trained in a free-operant situation produce a sharper gradient of generalization around a specific irrelevant stimulus if they are given true discrimination (TD) training than if given pseudodiscrimination (PD) training. An additional pair of groups, however, showed that this difference could be eliminated if, after initial training but before the test for generalization, both TD and PD Ss were given TD training on an entirely independent set of stimuli. This suggests that the normally flat PD gradient may represent a test effect: control by the specific irrelevant stimulus is masked by other more powerful irrelevant stimuli that are only suppressed by TD training. Exp. II demonstrated that in a discrete-trial situation, PD training results in a sharper gradient than does TD training, suggesting that the other unidentified irrelevant stimuli are present only in free-operant situations. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to the unconditioned stimulus alone: Effects on retention and acquisition of conditioned suppression.

In 3 experiments with 104 male Sprague-Dawley rats, repeated exposure to an electric-shock UCS resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory CS and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock. Exp I showed that 10 sessions of exposure to shock alone were required to produce a decrement in retention of conditioned suppression, whereas retardation in the acquisition of conditioned suppression was obtained following either 5 or 10 sessions of exposure to shock alone. Exp II demonstrated that both of these effects were directly related to the intensity of the shocks. In Exp III, the decrement in retention of conditioned suppression produced by 10 sessions of exposure to shock alone was inversely related to the interval between the last exposure to shock and the test of the target CS. Findings are discussed in terms of associative and nonassociative accounts of the effects of UCS-alone procedures. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)