Is extinction the hallmark of operant discrimination?: Reinforcement and S effects

Using a successive discrimination procedure with rats, three experiments investigated the contribution of reinforcement rate and amount of S(Delta) exposure on the acquisition of an operant discrimination. S(D) components and were always 2 min in length, while S(Delta) (extinction) components were either 1 min or 4 min in length; responses in S(D) were reinforced on one of four schedules. In Experiment 1, each of eight groups were exposed to one possible combination of rate of reinforcement and S(Delta) component length. At every level of reinforcement, the 4 min S(Delta) groups acquired the discrimination more quickly. However, within each level of reinforcement, the proportions of responding in S(D) as a function cumulative S(Delta) exposure were equivalent, regardless of the number of reinforcers earned in S(D), suggesting that extinction is the "hallmark" of discrimination. Experiment 2 sought to replicate these results in a within-subjects design, and although the 4 min S(Delta) conditions always produced superior discriminations, the lack of discriminated responding in some conditions suggested that stimulus disparity was reduced. Experiment 3 clarified those results and extended the finding that the acquisition of operant discrimination closely parallels extinction of responding in S(Delta). In sum, it appears that higher reinforcement rates and longer S(Delta) exposure facilitate the acquisition of discriminated operant responding.     

Determinants of tonic and phasic reactions in transswitching

Forty-eight college students were assigned randomly to four groups in a 2 X 2 factorial arrangement of phasic conditional stimuli (same vs. different) and tonic conditional stimuli (same vs. different) to receive 2 days of classical conditioning with a transswitching procedure. Tonic stimuli were a 5-minute projected white triangle or circle; phasic stimuli were a 5-second red or green square superimposed over the tonic stimuli. There were six tonic stimulus segments each day, separated by 20-second periods of no stimulus, three containing six trials of the phasic stimulus paired with shock and three containing six trials of the phasic stimulus alone, in the counterbalanced order. Tonic responding at the onset of the tonic stimuli or during brief periods following its onset were recorded, along with phasic responses to the phasic stimuli. Responses included magnitude of skin conductance responses, frequency of unelicited skin conductance responses, and tonic heart rate. Both skin conductance measures of responding to the tonic stimuli differentiated significantly between positive and negative tonic segments during Day 2, but only in the group with two different tonic stimuli and one phasic stimulus ("standard" transswitching). This supported the hypothesis that tonic stimulus differentiation would be absent when two different phasic stimuli were present. The heart rate data did not support this hypothesis, showing tonic differentiation in both groups with two tonic stimuli. Phasic differentiation controlled by the different phasic stimuli was observed on Day 1; on Day 2, phasic differentiation was present only in the group with two tonic and one phasic stimuli and the group with one tonic and two phasic stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of inter-trial interval length on food-hoarding partial reinforcement of running behaviour in the golden hamster

Food-hoarding provides an adequate motivation in sated hamsters for the acquisition of a two-way running response. This learning was studied using a discrete-trial procedure, in continuous (CR) and partial reinforcement (PR) conditions, with two different inter-trial interval (ITI) lengths. The dependent variables were: the time spent by Ss in the goal section of the runway, and the number of their runs during extinction.The PR training had two effects on goal times: a slow decrease in acquisition on non-reinforced trials, and then a stabilization at this level during the extinction phase, as contrasted with the sudden increase found in CR-trained Ss when they were switched from acquisition to extinction conditions. However, the PR effects on number of runs depended upon ITI length: resistance to extinction of PR-trained Ss was superior to that of CR-trained Ss with spaced, but not with massed, trials. In the latter case, CR-trained Ss persisted as much as did PR-trained Ss. An hypothesis is offered, along the lines of the Frustration theory.     

Superstitious responding and reinforcement rate under concurrent variable-interval extinction schedules

To examine superstitious responding, four pigeons key pecked under multiple concurrent variable-interval 45 s variable-interval 90 s concurrent variable-interval 90 s variable-interval 180 s schedules in the absence of a changeover delay. The two variable-interval 90 s schedules then were replaced by extinction, and key-peck responding during extinction was examined as a function of the prevailing reinforcement rate. During the first several sessions, extinction-key responding was maintained closer to baseline levels in the presence of the higher reinforcement rate, and this effect dissipated or even reversed with continued exposure to extinction. Although extinction-key responding generally decreased to near-zero levels after several sessions, in a few instances, it continued for 30 and 45 sessions. These results demonstrate how concurrent variable-interval extinction schedules can be used to investigate what often has been labeled superstitious responding.     

Prolonged microwave irradiation of rats: Effects on concurrent operant behavior

Two measures of performance were used to study the effects of pulse-modulated microwave radiation (PM MWR) on schedule-controlled operant behavior of rats: 1) cued (S^D), fixed-ratio (FR) bar pressing for food reinforcement; and 2) noncued (S^d) bar pressing in the absence of food reinforcement. The animals were irradiated and the behavioral data were obtained concurrently, during daily three-hour sessions, five days per week for six to nine weeks. Each experiment began with a two to three-week baseline interval of sham irradiation; a two to three-week interval of sham irradiation followed the irradiation phase. The irradiated animals were exposed to 1.3-Ghz PM MWR (pulse width of 1 microsecond at 600 pulses per second) at whole-body, average specific absorbed-dose rates of from 1.5–6.7 mW/g. Control and irradiated animals were tested in identical, cylindrical waveguide exposure/behavioral assemblies; different groups of irradiated and sham-irradiated animals were used for each dose rate. At 1.5 mW/g, the levels of S^D operant responding by control and irradiated animals were comparable, and showed similar progressive diminutions over the course of each daily session. S^d operant responding was more variable, but again comparable, with both groups showing similar, progressive declines in rate of responding during each session. At 3.6 mW/g, no specific effects on S^D operant response rates were observed. However, there was an initial and transient increase in the rate of extinction of S^d responding. At 6.7 mW/g, S^D response rates were slightly reduced, whereas there was a major reduction in noncued (S^d) operant responding followed by a sharp rebound during the first post-MWR week. This marked reduction in S^d operant responding at MWR onset was in contrast to the relative stability and persistence of FR responding for food reinforcement.     

Strictly simultaneous classical eyelid conditioning in man

Strictly simultaneous eyelid conditioning in human Ss on the one hand and forward (ISI: 0.45 s), backward (ISI: -0.45 s), and pseudoconditioning on the other hand were compared in two different experimental situations: one-session experiment (100 reinforcements, 20 isolated CS randomly interspersed), and ten-sessions experiment (20 reinforcements, 4 isolated CS in each session), UCS was a light flash (0.5 J, 20 microseconds duration), CS a tone (1000 Hz, 50 ms, 73 dB). In both the experiments, strictly simultaneous conditioning was significantly different from pseudoconditioning, but significantly less effective than forward conditioning. In the ten-sessions experiment, it was also less effective than backward conditioning, while in the one-session experiment, it did not differ from backward conditioning. Statistical mixture decomposition method applied to the one-session- and the ten-sessions- experimental samples of individual acquisition curves resulted into the division of both samples into 4 subgroups according to the trend of acquisition curves. A significant positive association between the conditioning procedure and the distribution of individual curves into the four subgroups was found.     

Companion's effects upon resistance to change

In order to investigate the effects of a companion's presence on resistance to change, five rats were trained under a multiple schedule comprised of components with high versus low rate of water reinforcement. After response rates became stable, water was given to the subjects prior to the experimental sessions, and these were conducted both in the absence and in the presence of a companion, which also could be responding or merely present. Results showed that the companion's presence increased resistance to satiation, mainly during the component with the higher reinforcement rate. These results suggest that the effect of the companion's presence may interact with reinforcement rate in determining response rate and resistance to satiation.     

Contextual stimulus control of conditional vasomotor and electrodermal reactions to angry and friendly faces. Transswitching--yes! Preparedness--No!

An experiment with 42 human Ss used the transswitching procedure to examine tonic stimulus control of phasic and tonic conditioned vasomotor heart rate, and electrodermal reactions. The conditional stimulus (CSs) were photos of angry and friendly human faces, and the unconditional stimulus (US) was a human scream. In one tonic context (blue light), the CSs were paired with the US, in the other context (yellow light), the CSs were presented unpaired. Following acquisition, an extinction series was run with the US omitted during both tonic contexts. Phasic vasomotor and skin conductance reactions differed in the positive and negative tonic segments (stronger in positive). The skin conductance responses also differed during extinction, but the vasomotor responses did not. Tonic differences (following onset of the tonic stimuli) in unelicited skin conductance response frequency, finger pulse volume, and heart rate were also found, although these developed more slowly than the phasic differences. The finger pulse volume tonic difference was greater in extinction than the skin conductance response frequency. There was no effect of the angry-friendly facial expressions, either directly or in interaction with the transswitching effects. The results were interpreted to mean that the transswitching phenomenon is not limited to one another autonomic effector, but is more generalized across the ANS (sympathetic branch). The absence of influence of the facial expressions indicates the relative weakness of the "preparedness" hypothesis in comparison with more influential contextual factors.     

Fewer peak trials per session facilitate acquisition of peak responding despite elimination of response rate differences

It has been shown in previous research [Kaiser, D.H., 2008. The proportion of fixed interval trials to probe trials affects acquisition of the peak procedure fixed interval timing task. Behav. Process., 77 (1), 100-108] that rats acquired peak responding sooner when fewer peak trials were presented during sessions of training with the peak procedure timing task. One potential problem with that research was that there were large differences in response rates among the groups. The present experiment attempted to examine the effect of proportion of peak trials when differences in response rate were controlled. Two groups of rats were each simultaneously tested with two versions of the peak procedure. One group was tested with 10% peak trials per session, and the other group was tested with 50% peak trials per session. For both of the groups, one of the panel lights and levers was associated with the traditional peak procedure. The other panel light and lever was associated with a similar peak procedure; however, reinforcement was provided at the end of each peak trial. This manipulation eliminated differences in response rate among the groups, however, Group 10% acquired peak responding more quickly than Group 50%, effectively replicating previous work in the absence of a response bias.     

Time estimation by pigeons on a fixed interval: the effect of pre-feeding

Pigeons well trained on a fixed interval 10-s schedule of reinforcement were tested on the peak procedure. In a successive conditions design, they were either pre-fed or not in the experimental setting. Pre-feeding decreased the rate of responding. It also led to a maximum rate of responding that occurred 2-3 s later than in the control condition, where the maximum occurred at the usual time of reinforcement. The shift in peak time in response to pre-feeding shows that peak time may not be a pure measure of timing. The results are also interpreted in terms of timing theories.     

凉血活血汤联合阿维A胶囊治疗银屑病的临床疗效及其机制研究

目的:探讨凉血活血汤联合阿维A胶囊治疗银屑病的临床疗效及其可能作用机制。方法:选择2012年7月~2015年11月于我院就诊的银屑病患者60例,按照就诊先后顺序分为实验组与对照组,每组各30例,实验组患者使用凉血活血汤联合阿维A胶囊进行治疗,对照组患者仅给予阿维A胶囊进行治疗。比较治疗前后两组患者血清白细胞介素17(IL-17)、白细胞介素22(IL-22)、白细胞介素23(IL-23)及血管内皮因子(VEGF)水平,同时比较两组患者的不良反应发生率及临床总有效率。结果:与治疗前相比,两组患者血清IL-17、IL-22、IL-23及VEGF水平均降低;治疗结束后与对照组相比,实验组患者血清IL-17、IL-22、IL-23及VEGF水平较低(P0.05);且与对照组相比,实验组患者的不良反应发生率较低(P0.05);临床总有效率较高(P0.05)。结论:凉血活血汤联合阿维A胶囊能明显提高银屑病患者的临床疗效,且安全性较高,可能与其降低血清IL-17、IL-22、IL-23及VEGF水平有关。     

The proportion of fixed interval trials to probe trials affects acquisition of the peak procedure fixed interval timing task

A common procedure for studying the ability of animals to time is the peak procedure. With the peak procedure, animals are first trained on a fixed interval schedule (i.e., 30s). After the animals have been well trained on the fixed interval schedule, probe trials are introduced. On probe trials, the stimulus is presented longer (i.e., 90s) and the animal does not receive reinforcement for responding. When animals are first presented with probe trials responding remains flat following the point that reinforcement normally occurs on fixed interval trials. The descending slope that eventually emerges is acquired with experience with probe trials. The present experiments manipulated the percentage of probe trials compared to FI trials across groups of rats. It was hypothesized that the descending limb of peak responding would be acquired more quickly when there were many probe trials per session as this might facilitate extinction of responding beyond the interval that reinforcement normally occurs. It was found, however, that acquisition of peak responding occurred best when there were few probe trials per session.     

Effect of unsignaled delays between stimuli in a chain schedule on responding and resistance to change

Behavioral momentum theory is an evolving theoretical account of the strength of behavior. One challenge for the theory is determining the role of signal stimuli in determining response strength. This study evaluated the effect of an unsignaled delay between the initial link and terminal link of a two-link chain schedule on resistance to change using a multiple schedule of reinforcement. Pigeons were presented two different signaled delay to reinforcement schedules. Both schedules employed a two-link chain schedule with a variable interval 120-s initial link followed by a 5-s fixed time terminal link schedule. One of the schedules included a 5-s unsignaled delay between the initial link and the terminal link. Resistance to change was assessed with two separate disruption procedures: extinction and adding a variable time 20-s schedule of reinforcement to the inter-component interval. Baseline responding was lower in the schedule with the unsignaled delay but resistance to change for the initial link was unaffected by the unsignaled delay. The results suggest that not all unsignaled delays are equal in their effect on resistance to change.     

"The stone which the builders rejected...": Delay of reinforcement and response rate on fixed-interval and related schedules

The article deals with response rates (mainly running and peak or terminal rates) on simple and on some mixed-FI schedules and explores the idea that these rates are determined by the average delay of reinforcement for responses occurring during the response periods that the schedules generate. The effects of reinforcement delay are assumed to be mediated by a hyperbolic delay of reinforcement gradient. The account predicts that (a) running rates on simple FI schedules should increase with increasing rate of reinforcement, in a manner close to that required by Herrnstein's equation, (b) improving temporal control during acquisition should be associated with increasing running rates, (c) two-valued mixed-FI schedules with equiprobable components should produce complex results, with peak rates sometimes being higher on the longer component schedule, and (d) that effects of reinforcement probability on mixed-FI should affect the response rate at the time of the shorter component only. All these predictions were confirmed by data, although effects in some experiments remain outside the scope of the model. In general, delay of reinforcement as a determinant of response rate on FI and related schedules (rather than temporal control on such schedules) seems a useful starting point for a more thorough analysis of some neglected questions about performance on FI and related schedules.     

Isolated effects of number of acquisition trials on extinction of rat conditioned approach behavior

Four conditioned approach experiments with rats assessed for effects of number of acquisition trials on extinction of conditioned responding, when number of acquisition sessions and total acquisition time were held constant. In Experiment 1, 32 trials per acquisition session led to more extinction responding than did 1 or 2 trials per session but less than did 4 trials per session. In Experiment 2, 2 trials per acquisition session led to more spontaneous recovery than did 32 trials per session. These latter findings are reminiscent of the overtraining extinction effect (OEE). Experiment 3 attempted to reduce the OEE with a preconditioning phase of partial reinforcement. Experiment 4 attempted to reduce the beneficial within-subject effects of increasing the number of acquisition trials on extinction observed by Gottlieb and Rescorla (2010) by extinguishing stimuli in different sessions. Overall, results suggest a procedural asymmetry: between-subject, increasing the number of trials between any pair of trials does not lead to greater persistence of responding during extinction; within-subject, it does. Results are discussed from an associative perspective, with a focus on explanations involving either frustration or comparator mechanisms, and from an information processing perspective, with a focus on Rate Estimation Theory.     

Thyrotropin-releasing hormone action in the preoptic/anterior hypothalamus decreases thermoregulatory set point in ground squirrels.

Earlier work has shown that thyrotropin releasing hormone (TRH) produces dose-dependent decreases in body temperature (Tb) and metabolic rate when microinjected into the dorsal hippocampus (HPC) or preoptic/anterior hypothalamus (PO/AH) of awake ground squirrels. This study employed a behavioral paradigm to investigate the possibility that TRH-induced hypothermia is associated with a decrease in thermoregulatory set point. Six animals were successfully trained to press a bar for radiant heat escape and cool air reinforcement in order to obtain a cooler ambient temperature (Ta). During experimental testing, the animals were microinjected remotely with TRH (10-1000 ng/microliters) or a control solution (sterile saline or TRH-OH) into the PO/AH. The micro-injections were delivered via bilateral injection cannulae inserted through chronic bilateral cannula guides that had been stereotaxically implanted under pentobarbital anesthesia. Cumulative and time-integrated bar presses were obtained on a computer generated display. Tb, measured in the brain via a bead-type thermistor, and chamber Ta were recorded continuously. Following TRH administration, a significant increase in mean bar-press rate was observed during the period in which Tb was falling, when compared to a comparable time period just prior to the microinjection. These findings complement results obtained from four animals that were trained to press a bar for heat reinforcement in a cold (- 10 degrees C) environment. In this alternative behavioral paradigm, microinjection of TRH into the PO/AH or HPC induced a decrease in mean bar-press rate as Tb was falling. The results support the hypothesis that TRH-induced hypothermia in golden-mantled ground squirrels is achieved by lowering thermoregulatory set point.     

Resistance to variable-time schedules produced by spaced-response reinforcement schedules

Two experiments are reported in which rats were exposed to either a tandem fixed-ratio 1 differential-reinforcement-of-low-rate 10 sec schedule (tand FR1 DRL 10) (Experiment 1) or to a DRL 10 sec schedule (Experiment 2) prior to being exposed to a variable-time (VT) schedule. Response decrement was not universally found during the VT phase, one rat emmitting an increase in response rate relative to baseline (Experiment 1), while another showed neither an increase nor decrease during VT relative to baseline (Experiment2). The VT schedule induced less efficient responding in both experiments. Interresponse time (IRT) distributions (Experiment 2) indicated that the VT changed the pattern of responding. These results, when combined with others from our laboratory, indicate that although unsignalled variable delay of reinforcement may be a sufficient condition for producing resistance to response-independent reinforcement, it is not a necessary condition. It was concluded that a response competition model of the kind proposed by Henton and Iversen (1978) might have explanatory merit in this kind of experimental situation.     

Chronic functional ethanol tolerance in mice influenced by body temperature during acquisition

Previous studies have found that body temperature during intoxication influences brain sensitivity to ethanol with the sensitivity being less at cool than at warm body temperatures. If this effect of temperature reflects alterations in the acute membrane perturbing action of ethanol, as suggested by in vitro studies, then body temperature reduction (hypothermia) during tolerance acquisition should reduce the effectiveness of a given ethanol concentration and, in turn, should reduce the development of chronic functional ethanol tolerance. To test this hypothesis, adult drug-naive C57BL/6J mice were injected i.p. once daily for five days with 3.6 g/kg ethanol (20% w/v) and were exposed to 34 degrees C or 25 degrees C for five hours following injection. On day 6, both ethanol acquisition groups and naive mice were injected i.p. with 4.0 g/kg ethanol and exposed to 25 degrees C. During acquisition, the group exposed to 34 degrees C had significantly higher body temperatures than the mice exposed to 25 degrees C, and there were no statistically significant differences in blood ethanol concentrations between treatment conditions. The extent of tolerance on day 6, measured by sleep-times and wake-up blood and brain ethanol concentrations versus naive mice, was significantly greater in the 34 degrees C acquisition group than in the 25 degrees C acquisition group. The results demonstrate that body temperature influences tolerance development in the manner predicted by membrane perturbation theories of anesthesia and adaptation based tolerance theories.     

Amphetamine affects the start of responding in the peak interval timing task

In this paper we investigate how amphetamine affects performance in a PI task by comparing two analyses of responding during peak trials. After training on 24 s fixed interval (FI-24) with 96 s peak trials, rats were given amphetamine for 4 consecutive days at doses of .5 and 1.0 mg/kg. Responses during peak trials were fitted with a Gaussian distribution to estimate the expected time of reinforcement from the peak time. A single trials analysis was also performed to determine the start time and stop time of the transition into and out of a high rate of responding on each peak trial. Amphetamine significantly decreased peak times as measured with the Gaussian curve fitting. However, in the single trials analysis, animals initiated responding significantly earlier, but did not stop responding earlier. Thus, fitting a Gaussian to the average performance across trials sometimes provides a different characterization of the timing process than does analyzing the start and stop of responding on individual trials. In the current experiment, the latter approach provided a more precise characterization of the effects of amphetamine on response timing.     

The comparison between cool and warm-hot environments on lipolytic response during prolonged exercise

The purpose of this study was to investigate the effect of cool exposure on lipolytic response during prolonged intermediate-intensity exercise in humans. Eight male subjects participated in this study; they performed 120-min cycle ergometer exercise at 60% of maximal oxygen uptake (VO2max) in a climatic chamber at 10 degrees C (C) and 30 degrees C (WH). There were no significant differences in oxygen uptake and respiratory exchange ratio between the two conditions during the prolonged exercise. Significant influences of cool exposure were observed in the changes in both heart rate and rectal temperature (p<0.01). Although cool exposure had no significant effects on plasma triglyceride, free fatty acid, and glycerol levels, changes in adrenaline and noradrenaline levels at C were significantly lower than WH during the prolonged exercise (p<0.01). Changes in the ratio of glycerol to noradrenaline (Gly/Nad), as an index of lipolytic efficiency, were significantly high at C as compared with WH (p<0.01). These results suggest that cool exposure has an influence on lipid metabolism during prolonged intermediate-intensity exercise, from the viewpoint of efficiency in lipolysis.