Effects of schedule and magnitude of reinforcement under conditions of thirst motivation

In contrast to a recent finding (Macdonald, G. E., & De Toledo, L. Learning and Motivation, 1974, 5, 288–298.) the results of three experiments investigating various partial reinforcement (PRF) manipulations under conditions of thirst motivation demonstrated strong similarity to analogous manipulations involving food reward. Specifically, for animals receiving water reinforcement, PRF was shown to generate greater resistance to extinction than continuous reinforcement (Expt 1 & 3), the schedule of reinforcement was shown to interact with level of acquisition (Expt 1 and 2), and the magnitude of the partial reinforcement extinction effect was shown to be a function of reward magnitude (Expt 3). These results provide strong evidence that mechanisms which operate in partial reinforcement situations are highly similar, regardless of the type of appetitive reinforcement.     

Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.     

Persistence of response prevention effects following retraining of escape behavior

This study evaluated the effects of response prevention procedures on the extinction of escape behavior following the reinstatement of shock-escape training prior to the start of extinction. Female hooded rats were assigned to four groups (N = 10) in a factorial design which orthogonally combined response prevention or pseudo-prevention procedures with escape retraining or no retraining procedures. Results showed that prevention reliably impaired shock-escape behavior on early retraining trials; but this effect dissipated completely by the end of retraining. In extinction, prevention reliably facilitated the extinction of escape behavior relative to that of pseudo-prevention controls; but the degree of facilitation was reliably attenuated by retraining procedures. These findings were related to the competing response interpretation of prevention effects.     

Relationships among vocational training,income, and job complexity of high school dropouts and high school graduates

High school dropouts (N = 100) and high school graduates (N = 100), of which half of each group had received vocational training and the other half had not, were compared on data taken from the inactive employment applications of the Fort Walton Beach, Florida State Employment Office. The sample (N = 200) consisted of an equal number of males and females while 30% were minority group members. A two-way analysis of variance showed that completing vocational training was positively correlated with higher income and job complexity level. The existence or absence of vocational training was a more potent influence on income level and job complexity than was completion of high school.     

Factors affecting the acquisition and elimination of children's donating behavior

Thirty-five 6- to 10-year-old children with initial low rates of donating to help a peer either simply received a fine for each failure to donate (n = 7) or also were informed of the contingency between the fine and failure to donate (n = 28). Explanation of the contingency was necessary to increase children's donation rates. Donations continued at high rates during a gradual, unannounced removal of the fine contingency, but decreased when children were informed that fines were no longer in effect, particularly for children who had failed to donate at least once during training and had actually been fined. Overall, addition of a distraction or an inequity procedure did not reduce donating below rate reductions due to the announced extinction procedure alone.     

Partial reinforcement effects in instrumental escape conditioning

In Experiment I acquisition and extinction of instrumental escape conditioning with rats (N = 64) were studied as a function of reinforcement magnitude under conditions of partial and continuous reinforcement. In Experiment II the effects of partial and continuous reinforcement were studied in rats (N = 96) during acquisition followed by small, medium, and large reductions in reinforcement magnitude. A water-tank escape apparatus was used with temperature as the relevant variable. It was found that (1) with large reinforcement magnitude a continuously reinforced group was superior in acquisition to one that was partially reinforced; there were no differences with small reinforcement; (2) disruptive effects of a nonreinforced trial (a) appear early in learning, (b) are quite strong after each nonreinforced trial, and (c) persist through several succeeding reinforced trials; (3) major competing behaviors persist throughout acquisition for small reinforcement magnitude regardless of schedule, decline with large reinforcement (more so with continuous than with partial), and return to a high level in extinction for all conditions; (4) the partial reinforcement extinction effect occurs after large reinforcement but not after small, and it appears only with large reductions in reinforcement magnitude which approach extinction conditions. Only the first part of the last finding appears to be consistent with the appetitive conditioning literature.     

Cocaine self-administration alters the relative effectiveness of multiple memory systems during extinction

Rats were trained to run a straight-alley maze for an oral cocaine or sucrose vehicle solution reward, followed by either response or latent extinction training procedures that engage neuroanatomically dissociable “habit” and “cognitive” memory systems, respectively. In the response extinction condition, rats performed a runway approach response to an empty fluid well. In the latent extinction condition, rats were placed at the empty fluid well without performing a runway approach response. Rats trained with the sucrose solution displayed normal extinction behavior in both conditions. In contrast, rats trained with the cocaine solution showed normal response extinction but impaired latent extinction. The selective impairment of latent extinction indicates that oral cocaine self-administration alters the relative effectiveness of multiple memory systems during subsequent extinction training.Understanding the psychological and neural mechanisms underlying the acquisition and extinction of drug-seeking behavior has important implications for therapies targeting drug addiction. A better understanding of the neurobiology of extinction can potentially allow for the development of treatments to produce more effective and persistent extinction learning. Dissociable hippocampus-dependent “cognitive” and dorsal striatal-dependent “habit” memory systems are engaged during the initial acquisition of learned behavior (for reviews, see Packard and Knowlton 2002; White and McDonald 2002; Squire 2004). Interestingly, recent evidence indicates that multiple memory systems can also be engaged during the new learning that occurs during behavioral extinction (Gabriele and Packard 2006). For example, the behavior of a rat trained to traverse a straight-alley runway for a food reward can be extinguished using either habit/response or cognitive/latent extinction training procedures. During response extinction, rats are allowed to perform the runway approach response to an empty food cup. In contrast, during latent extinction, rats are placed at the empty food cup without performing the runway approach response. Consistent with evidence indicating a selective role for the hippocampus in cognitive memory, neural inactivation of this brain structure impairs latent extinction and spares response extinction (Gabriele and Packard 2006). Moreover, consistent with evidence that the dorsal striatum selectively mediates habit memory (for review, see Packard and Knowlton 2002), neural inactivation of this brain region impairs response extinction and spares latent extinction (A. Gabriele and M.G. Packard, unpubl.).The transition from initial drug use to eventual addiction may involve, at least in part, the development of compulsive drug-seeking and drug-taking behaviors that are increasingly guided by dorsal striatal-dependent habit learning mechanisms (for reviews, see White 1996; Everitt et al. 2001; Everitt and Robbins 2005; Belin et al. 2008). This hypothesis raises the possibility that once “habit-like” drug-seeking behaviors are firmly acquired, the extinction of such behaviors may be differentially influenced by engaging habit and cognitive memory systems. In the present study, we examined this idea by comparing the relative effectiveness of response and latent extinction training procedures in rats trained to run a straight-alley maze for an oral cocaine reward. Consistent with criteria considered important for demonstrating drug dependence, oral cocaine self-administration produces withdrawal following forced abstinence (Barros and Miczek 1996) and additionally is resistant to reinforcer devaluation (Miles et al. 2003), indicating that this behavior becomes divorced from its consequences in a manner similar to the dorsal striatum-mediated compulsive drug-seeking behavior that may characterize addiction (for reviews, see White 1996; Everitt et al. 2001; Everitt and Robbins 2005; Belin et al. 2008).The apparatus was an elevated (86.4 cm) straight-alley maze with a black Plexiglas floor and clear Plexiglas sides (117.8 cm long, 11.4 cm wide, and 20.3 cm tall). A fluid cup (2.5-cm diameter) was located at the goal end of the maze. The maze was located in a room containing several extra-maze cues.Subjects were 32 adult male Long-Evans rats (275–300 g). Rats were individually housed on a 12:12-h light–dark cycle, with lights on from 8:00 a.m.–8:00 p.m. All animals received food ad libitum.During all behavioral procedures, water bottles were removed from home cages 24 h prior to training, and animals received 15 min/day access to water following each day''s procedures. Training began with 3 d of habituation to the solution to be used during training (cocaine–sucrose [0.1% cocaine HCl/20% sucrose in ddH₂0] or sucrose [20% in ddH₂0] alone). Each habituation day involved presentations of 0.5 mL of the solution in a novel environment consisting of a half-white, half-black box (41.9 cm long, 31.8 cm wide, 35.6 tall) with the fluid cup located in the center of the black side. The number of presentations increased with each habituation day (1, 2, and 4). Each individual presentation had a maximum time of 20 min, and rats were removed when the solution was consumed. Volume consumed and amount of time to consume the solution were recorded for each rat. Each sucrose rat was matched to a cocaine rat to ensure that there were no differences between groups in terms of volume of solution consumed prior to training. For each matched pair, the volume consumed by the rat receiving the cocaine solution during each presentation was measured, and an identical amount was made available to the matched sucrose animal. If, during any given presentation, the cocaine animal did not consume any solution, then the matched sucrose animal received 20 min in the habituation environment with no solution present.Behavioral procedures were similar to those of our previous study using food reward (Gabriele and Packard 2006). During maze training, animals received either the cocaine–sucrose solution or sucrose vehicle solution reward. On days 1–10 of solution-rewarded maze training (six trials per day), rats were placed in the start end and allowed to traverse the maze and drink the available reward solution (0.5 mL). Upon consuming the solution, rats were removed from the maze and placed in an opaque holding box adjacent to the maze for a 30-sec intertrial interval. On each trial, the latency (in seconds) to reach the fluid cup was recorded and used as the measure of task acquisition. If a rat failed to reach the fluid cup within 60 sec, it was removed for the intertrial interval and a latency of 60 sec was recorded.Twenty-four hours following the completion of training (i.e., day 11), rats were assigned to one of two extinction conditions; latent extinction (n = 18, 10 cocaine and eight sucrose) or response extinction (n = 14, seven cocaine and seven sucrose). For both the latent and response conditions, extinction training was administered over 3 d (six trials per day, 30-sec intertrial interval) with no reward solution present. In the latent extinction condition, rats were placed facing the empty fluid cup in the goal end of the maze and were confined for 60 sec by placement of a clear Plexiglas barrier 20 cm from the rear wall of the goal end of the maze. Following confinement, rats were removed from the maze and placed in the holding box for the 30-sec intertrial interval. In the response extinction condition, rats were placed into the start end of the maze as during training and allowed to run to an empty fluid cup at the goal end of the maze. Upon reaching the empty fluid cup and being allowed to discover its emptiness (or after 60 sec if the rat did not reach the reward cup), rats were removed from the maze and placed in the holding box for the 30-sec intertrial interval. Latency to reach the fluid cup was recorded and used as the measure of extinction behavior. On day 3 of extinction, 90 min following the sixth daily extinction trial, all rats were given an additional four extinction “probe” trials in which they were placed in the start end of the maze and latency to reach the empty fluid cup was recorded. These four trials allowed for an assessment of the effectiveness of each extinction procedure.Data from the runway acquisition sessions are presented in Figure 1. A two-way one-repeated-measure ANOVA (Group [cocaine vs. sucrose] × Session) comparing the latencies to reach the fluid cup during acquisition in rats that subsequently received latent extinction revealed a significant effect of Session (F_(9,16) = 61.03, P < 0.001), indicating that latency to reach the fluid cup during acquisition decreased across sessions. However, the absence of a main effect of Group (F_(1,16) = 1.94, n.s.) or interaction between Group and Session (F_(9,16) = 0.53, n.s.) indicates that rats trained to run for cocaine and sucrose acquired the task at similar rates (Fig. 1A). Similar results were observed in rats that subsequently received response extinction (Fig. 1B) in that there was a main effect of Session (F_(9,12) = 13.11, P < 0.001) but no main effect (F_(1,12) = 0.44, n.s.) or interaction (F_(9,12) = 1.50, n.s.) involving drug Group.Open in a separate windowFigure 1.Acquisition of maze runway behavior. (A) Acquisition of maze runway behavior by rats that subsequently received latent extinction. (B) Acquisition of maze runway behavior by rats that subsequently received response extinction. Mean ± SEM of latency (in seconds) to reach the solution cup over training days. For both extinction conditions, there were no group differences in the initial acquisition of runway behavior.The effects of oral cocaine self-administration on latent and response extinction are shown in Figure 2. A two-way ANOVA (Group × Extinction condition) comparing mean runway latencies (collapsed across the four probe trials) for each group revealed a significant main effect of Extinction condition (F_(1,28) = 32.440, P < 0.001), indicating that the response extinction procedures produced greater extinction of the runway response, and a significant interaction effect between Extinction condition and Group (F_(1,28) = 4.813, P < 0.05) but no effect of Group (F_(1,28) = 0.96, n.s.). Simple effects tests showed a significant effect of Group within the latent extinction condition (F_(1,16) = 5.688, P < 0.05) but not the response extinction condition (F_(1,12) = 0.663, n.s.), indicating that oral cocaine self-administration selectively impaired latent but not response extinction. Additionally, a two-way one-repeated-measure ANOVA (Group × Trial) computed on the latencies to reach the fluid cup during response extinction training revealed a main effect of Trial (F_(2,12) = 16.44, P < 0.001), but no significant main effect (F_(1,12) = 2.27, n.s.) or interaction (F_(2,12) = 0.88, n.s.) involving Group, further indicating that oral cocaine did not impair response extinction.Open in a separate windowFigure 2.Effects of oral cocaine self-administration on extinction. The effect of oral cocaine self-administration on runway latent and response extinction. Mean ± SEM latency (in seconds) to reach the fluid cup is shown over the four extinction probe trials. Oral cocaine self-administration impaired latent extinction, but did not impair response extinction.The present experiments investigated the effect of oral cocaine self-administration on response and latent extinction in a straight-alley maze. Following training, rats in the response extinction condition performed the approach response to an empty goal box, whereas rats in the latent extinction condition were placed in the goal box with no reward present. Consistent with previous studies using food reward (e.g., Seward and Levy 1949; Gabriele and Packard 2006), rats rewarded with a sucrose solution were able to extinguish the approach response following both response and latent extinction procedures. In contrast, rats rewarded with a cocaine solution displayed normal response extinction (see also Schoenbaum and Setlow 2005) but impaired latent extinction. The selective impairing effect of oral cocaine self-administration on latent extinction indicates that the drug does not impair processes that contribute to general maze behavior (e.g., motivational, motor, or sensory processes), as any such influence would also likely produce a deficit in response extinction.Previous findings indicate that latent extinction of runway behavior is hippocampus dependent, whereas response extinction is dorsal striatal dependent (Gabriele and Packard 2006; A. Gabriele and M.G. Packard, unpubl.). In view of evidence that the hippocampus and dorsal striatum mediate cognitive and habit learning mechanisms, respectively (for reviews, see Packard and Knowlton 2002; White and McDonald 2002; Squire 2004), the findings suggest that oral cocaine self-administration can affect the relative use of multiple memory systems during extinction learning. The medial prefrontal cortex and basolateral amygdala have been implicated in extinction of several forms of learned behavior, and prior cocaine exposure can impair some forms of extinction learning (Burke et al. 2006; Peters et al. 2008; Quirk and Mueller 2008). However, neural inactivation of medial prefrontal cortex or basolateral amygdala does not affect latent extinction of maze runway behavior (A. Gabriele and M.G. Packard, unpubl.), suggesting that cocaine-induced dysfunction of these structures does not account for the results observed here.One explanation of the cocaine-induced impairment of latent extinction is that the approach response acquired during task acquisition is guided by a supra-normal stimulus-response habit, thereby rendering cognitive learning mechanisms ineffectual during latent extinction training. Consistent with this possibility, drug-seeking behaviors underlying addiction may involve, at least in part, a transition from goal-directed behaviors to habitual behaviors that characterize the function of the dorsal striatal memory system (e.g., Tiffany 1990; White 1996; Packard 1999; Everitt et al. 2001; Porrino et al. 2004; Everitt and Robbins 2005; Belin et al. 2008). Indeed, recent evidence implicates the dorsal striatum in habitual drug-seeking behaviors. For example, intradorsal striatum administration of dopamine antagonists impairs cocaine seeking (Vanderschuren et al. 2005), and inactivation of the dorsal striatum attenuates drug seeking, following both abstinence and extinction (Fuchs et al. 2006; See et al. 2007). Interestingly, disconnection between the ventral and dorsolateral striatum impairs cocaine-seeking behavior (Belin and Everitt 2008), and extended cocaine use enhanced cue-selective firing in the dorsal striatum and reduced cue-selective firing in the ventral striatum in go/no go discrimination learning, indicating an accelerated shift to dorsolateral striatal control (Takahashi et al. 2007). In addition, dopamine release increases in the dorsal striatum of rats following presentation of a response-contingent cue associated with cocaine (Ito et al. 2002). Similar results from fMRI and PET studies of human cocaine addicts showed increased activation in the dorsal striatum (Garavan et al. 2000) and an increase in dopamine release within the dorsal striatum (Volkow et al. 2006) following cue-induced cravings.A second explanation of the cocaine-induced impairment in latent extinction is that drug intake during task acquisition may have affected hippocampal physiology in a manner that negatively impacted the hippocampus-dependent learning that subsequently mediates latent extinction. Consistent with this possibility, chronic cocaine exposure impairs subsequent performance of hippocampus-dependent tasks such as the Morris water maze and the win-shift radial arm maze task (Melnick et al. 2001; Quirk et al. 2001; Mendez et al. 2008). However, it should be noted that the impairments observed in the latter studies were observed following exposure to cocaine doses considerably higher than those used in the present oral self-administration study. Since the current experiments do not explicitly examine the potential neurobiological progression underlying the acquisition of runway responding, further research is necessary to determine whether the cocaine-induced impairment of latent extinction involves the interfering effect of a supra-normal response habit, or a direct impairing effect on hippocampal physiology. It should also be noted that both oral cocaine self-administration and a passive cocaine administration regimen produce results analogous to those presented here, in that they impair “cognitive” representations of rewards (Miles et al. 2003; Schoenbaum and Setlow 2005). However, the relationship between this type of cognitive reward representation (mediated by interactions between basolateral amygdala and orbitofrontal cortex) (Pickens et al. 2003) and cognitive representations in latent extinction mediated by the hippocampus (Gabriele and Packard 2006) is currently unclear.Finally, the selective impairing effect of cocaine self-administration on latent extinction may have implications for understanding the persistent ability of drug-predictive cues and contexts to compel drug-seeking behavior and relapse. Specifically, if the ability to use cognitive learning mechanisms to extinguish drug-seeking behaviors is impaired following the transition from initial to habitual and compulsive drug use, then contextual/relational cues might be expected to maintain greater control over behavior following extinction training. This in turn might suggest that incorporation of response extinction procedures into treatment strategies might provide greater therapeutic efficacy.     

Preextinction Stress Prevents Context-Related Renewal of Fear

Extinction learning, which creates new safety associations, is thought to be the mechanism underlying exposure therapy, commonly used for the treatment of anxiety disorders and posttraumatic stress disorder. The relative strength and availability for retrieval of both the fear and safety memories determine the response in a given situation. While the fear memory is often context-independent and may easily generalize, extinction memory is highly context-specific. “Renewal” of the extinguished fear memory might thus occur following a shift in context. The aim of the current work was to create an enhanced and generalized extinction memory to a discrete stimulus using stress exposure before extinction learning, thereby preventing renewal. In our contextual fear conditioning paradigm, 40 healthy men acquired (Day 1), retrieved and extinguished (Day 2) the fear memories, with no differences between the stress and the control group. A significant difference between the groups emerged in the renewal test (Day 3). A renewal effect was seen in the control group (N = 20), confirming the context-dependency of the extinction memory. In contrast, the stress group (N = 20) showed no renewal effect. Fear reduction was generalized to the acquisition context as well, suggesting that stress rendered the extinction memory more context-independent. These results are in line with previous studies that showed contextualization disruption as a result of pre-learning stress, mediated by the rapid effects of glucocorticoids on the hippocampus. Our findings support research investigating the use of glucocorticoids or stress induction in exposure therapy and suggest the right timing of administration in order to optimize their effects.     

Stimulus control of responding in the early trials of differential conditioning

In Experiment 1 two groups of rats were given 12 differential conditioning trials, seven to the rewarded alley (S+) and five to the nonrewarded alley (S?), prior to being extinguished in both alleys. Group S?S+ received S+ trials, following S? trials in acquisition, while Group S+S? did not receive S+ trials following S? trials in acquisition. In extinction S+ and S? trials were presented according to a quasi-random sequence for both groups. Running on the last 3 trials of acquisition was found to be faster following S+ than following S? trials. Group S?S+ showed greater resistance to extinction and less discriminative responding in extinction than Group S+S?. These results suggest that responding in differential conditioning is controlled not merely by S+ and S? but by the memories of reward (S^R) and of nonreward (S^N) as well. When the joint effects of both classes of cues were considered, e.g., S^R+S+, responding in the early trials of differential conditioning was shown to be highly orderly. Experiment 2 was highly similar to Experiment 1 except that Groups S?S+ and S+S? were equated along dimensions not equated in Experiment 1. The results obtained in Experiment 2 were highly similar to those obtained in Experiment 1.     

The time course of extinction-induced aggressive behavior in humans: Evidence for a stage model of extinction

Three experiments examined the effects of extinction on aggressive responding in male college students. In Experiment 1 subjects initially performed on a task where shuttle responding was either continuously or partially reinforced with tokens while either a nonaggressive button-pressing response or an aggressive pad-striking response was concurrently reinforced by escape from a moderately aversive tone. During shuttle acquisition there was clear preference for the escape response of button pressing, but when shuttle responding was extinguished subjects began to respond aggressively by striking the pad to escape. The time course of aggressive escape responses during concurrent shuttle extinction was an inverted U; aggressive responding rose to a peak and then declined. Aggressive responding began earlier in extinction following continuous- as contrasted with partial-reinforcement shuttle training. Experiment 2 showed that similar extinction-induced aggression was precipitated by both moderate and extended continuous-reinforcement shuttle training, with earlier onset after extended reinforcement. Experiment 3 ruled out the possibility that the emergence of the pad-striking response during extinction was simply induced response variation. These data were interpreted within the theoretical framework of P.T.P. Wong's recently advanced stage model of extinction (Animal Learning and Behavior, 1978,6, 82–93).     

Effect of schedule and magnitude of reinforcement on instrumental learning in the toad, Bufo arenarum

Extinction after training with continuous (CR) or 50% partial (PR) reinforcement, and with different magnitudes of reward, was studied in the amphibian Bufo arenarum, in a runway situation. In Experiment 1, a group of toads received massed-trial, CR training with access to water as the reward. Performance improved during acquisition, including an improvement on the first trial of each session. Extinction was rapid and there was evidence for spontaneous recovery of the running response. In Experiment 2, groups of toads received PR or CR training at a rate of one trial per day. PR impaired acquisition and resulted in poor responding during extinction, compared to CR. Experiment 3 factorially studied the effects of schedule (PR vs CR) and distribution of practice (15 s vs 300 s intertrial interval). Acquisition was impaired by PR training but had little effect on extinction performance. Different magnitudes of water reinforcement were used in Experiment 4 in a one-trial-per-day situation. Terminal acquisition performance was a monotonic function of reward magnitude, but there were no differences in extinction performance across groups. The results are discussed in relation to comparative and developmental data on the paradoxical effects of reward.     

Stimulus- and pellet-induced drinking during a successive discrimination

In three experiments, interim water drinking was examined in rats exposed to a multiple schedule whose two components were extinction and a variable-time 30-s schedule of food delivery. Two different drinking patterns were observed in Experiment 1. Pellet-induced drinking, characterized by high rates of postpellet drinking in the variable-time component, with little or no drinking in extinction, occurred when the acquisition of stable postpellet drinking preceded discrimination training. Stimulus-induced drinking, characterized by a burst of drinking at the onset of extinction, with no drinking during the variable-time schedule, occurred when discrimination training preceded all other experimental conditions. With extended training, stimulus-induced drinking eventually was accompanied by postpellet drinking. In Experiment 2, the rate of stimulus-induced drinking and the number of sessions during which it occurred without postpellet drinking were found to be inversely related to component duration. In Experiment 3, the rate of schedule-induced drinking was found to vary directly with component duration.     

Belief similarity and attitude similarity as determinants of interpersonal attraction

It was predicted that attraction would be a function of both attitude similarity and belief similarity, but that attitude similarity would have the greater influence. In Expt I, 60 subjects were presented with strangers that were either similar or dissimilar on attitude and on belief. Attraction was a positive function of both attitude similarity (p < .05) and belief similarity (p < .01). Experiment II replicated and extended Expt I with the addition of a 50% similar group for both attitude and belief. Attraction was a positive linear function of both attitude similarity (p < .001) and belief similarity (p < .02); departure from linearity was not significant. Attitude similarity also had greater effects on other aspects of interpersonal evaluation than belief similarity. The results were discussed in terms of the locus of reinforcement of attitude similarity and of belief similarity.     

The partial punishment effect following minimal acquisition training: Sodium amobarbital and the stimulus properties of early punished trials

In a runway investigation, six groups of rats received limited runway training such that partial punishment, partial reinforcement, or continuous reinforcement was accompanied by sodium amobarbital or saline. Following an interpolated phase of continuous reinforcement without injections, all groups were given punished extinction. The entire experiment was conducted under widely spaced conditions (ITI = 24 hr). It was found that partial punishment increased resistance to punished extinction relative to partially and continuously reinforced controls when acquisition was given under saline. When partial punishment training was accompanied by amobarbital this effect was eliminated. The drug was observed to have no effect on the punished extinction performance of the partial reinforcement and continuous groups, respectively. Moreover, the partial reinforcement effect (PRE) did not generalize to punished extinction. These data provide information concerning the difference between the stimuli associated with the early trials of punishment and nonreward and indicate that the former but not the latter contain emotional elements.     

Punishment persistence and sequence: Some effects of P-length and N-length in the rat

In a runway investigation, two groups of rats received partial punishment training with P-lengths of 1, 2, and 3 (Group P123) and P-lengths of 1 (Group P1), respectively. Two additional groups received partial reinforcement with N-lengths of 1, 2, and 3 (Group N123) and N-length of 1 (Group N1). An additional group was given unpunished continuous reinforcement in the runway, but received control shocks in a separate apparatus. Following training all subjects received punished extinction (shock plus nonreward). The results indicated that P-length increased resistance to punished extinction, however N-length did not have the corresponding effect. In addition, partial reinforcement did not increase resistance to punished extinction relative to continuous reinforcement. These results were interpreted within a sequential-theoretical framework.     

Effects of UCS intensity and postpeak acquisition trials on classical conditioning of the SCR

The present study examined the effects of UCS intensity and number of postpeak acquisition trials on classical conditioning and extinction of the SCR. A 2 × 3 design was employed in which subjects received either a 1, 2, or 4 mA shock UCS and either two or 16 acquisition trials beyond the peak CR. While conditioning was demonstrated during acquisition, there was no relationship between strength of conditioning and intensity of UCS. The phenomenon of stronger resistance to extinction following fewer acquisition trials (e.g., two past the peak CR) than with many (e.g., 16 past the peak CR) was demonstrated only for the groups that were conditioned with the 4 mA UCS. Resistance to extinction varied positively with UCS intensity, but only for the subjects who received two postpeak acquisition trials. Sixteen trials beyond the peak CR resulted in the UCS intensity having little or no effect on resistance to extinction.     

Some determinants of behavioral contrast in pigeons and rats

In Expt. 1, pigeons trained on a multiple variable interval, extinction schedule, showed a positive contrast effect by comparison with control groups trained with S+ only, provided that the interval between stimulus presentations was short (10 sec), but not when it was long (60 sec). Positive contrast also occurred more readily with an easier discrimination, and its appearance was highly correlated with the temporary appearance of transient contrast effects. Although a longer interval between trials produced an overall increase in rate of responding in subjects trained only with S+, it was suggested that this at best represented a different type of contrast effect. In Expt. 2, rats showed positive contrast to S+ when S− was correlated with a lower frequency of reinforcement, but not when it was correlated with a reduced magnitude of reinforcement. The results were discussed in terms of frustration theory.     

Instrumental learning in preschool children as a function of type of task, type of reward, and some organismic variables

The effects on instrumental behavior of differences in type of task, type of reward and three organismic variables were investigated in preschool children. The main results were that: (a) an imitative task was acquired in fewer trials than a nonimitative task; (b) social reward in acquisition led to greater resistance to extinction; (c) a history of frequent social reinforcement from peers led to persistence in responding during extinction for boys only; (d) extraversion was found to interact with the variables of task and reward in errors made during extinction; and (e) intelligence was not found to be a reliable predictor of main acquisition and extinction measures or related errors. Detailed analysis of the different types of errors contributed directly to the interpretation of these findings.     

Aversive CSs suppress lever pressing for food but not the eating of free food

Forty rats received CER acquisition, half “on the baseline” (response lever present), half “off the baseline.” During initial CER extinction, Ss received: (a) normal CER extinction (lever available), (b) free food during CSs only (no lever), (c) free food during non-CSs only (no lever), or (d) free food during both CS and non-CS periods (no lever). While normal extinction Ss were highly suppressed in the presence of the CS, all free food groups readily ate but did not differ in eating latencies. On subsequent CER extinction trials on the baseline, those Ss which received free food during the CSs were no less suppressed than other Ss. These data offer no support for Estes' (1969) reciprocal inhibition explanation of CER and punishment, nor do they support a fear interpretation of CER.     

Modeling Hierarchical Versus Random Exposure Schedules in Pavlovian Fear Extinction: No Evidence for Differential Fear Outcomes

In exposure therapy, the client can either be confronted with the fear-eliciting situations in a hierarchical way or in a random way. In the current study we developed a procedure to investigate the effects of hierarchical versus random exposure on long-term fear responding in the laboratory. Using a fear conditioning procedure, one stimulus (CS +) was paired with an electric shock (US), whereas another stimulus was not paired with the shock (CS-). The next day, participants underwent extinction training including presentations of the CS-, CS + and a series of morphed stimuli between the CS- and CS +. In the hierarchical extinction condition (HE; N = 32), participants were first presented with the CS-, subsequently with the morph most similar to the CS-, then with the morph most similar to that one, and so forth, until reaching the CS +. In the random extinction condition (RE; N = 32), the same stimuli were presented but in a random order. Fear responding to the CS +, CS- and a new generalization stimulus (GS) was measured on the third day. Higher expectancy violation, t(62) = -2.67, p = .01, physiological arousal, t(62) = -2.08, p = .04, and variability in US-expectancy ratings, t(62) = -2.25, p = .03, were observed in the RE condition compared to the HE condition, suggesting the validity of this novel procedure. However, no differences between the RE and HE condition were found in fear responding as tested one day later, F(1, 62) < 1. In conclusion, we did not find evidence for differential long-term fear responding in modeling hierarchical versus random exposure in Pavlovian fear extinction.