Playful defensive responses in adult male rats depend on the status of the unfamiliar opponent

Adult male rats reared as pairmates from weaning were tested in a neutral arena with both members of another pair (one at a time). The unfamiliar pairs were found to engage in play fighting, although they were more likely to escalate the encounter into serious fighting than were pairs of familiar rats. Based on their within‐home pair behavior, each pairmate was designated as a dominant or a subordinate. When the test encounters between unfamiliar males were analyzed with regard to whether the pairings consisted of two dominants, two subordinates, or a mixed pair, the pattern of play fighting was found to be attenuated. Both dominants and subordinates were more likely to initiate playful encounters, to respond defensively during these encounters, and to do so using adult‐typical tactics of defense when paired with an unfamiliar rat that was dominant in its home cage. The mechanisms by which the home status of unfamiliar male rats can be identified by another male are discussed, particularly with regard to the role that play fighting may serve for this function. It is concluded that the data support the hypothesis that play fighting can be used by adult rats for social testing, which in this case seems to involve ascertaining the opponent's fighting capability. Aggr. Behav. 25:141–152, 1999. © 1999 Wiley‐Liss, Inc.     

Drugs and punished responding I: rate-dependent effects under multiple schedules

The effects of drugs were studied in pigeons whose responses were punished with electric shock during one component of a multiple fixed-interval 5-min fixed-interval 5-min schedule of food presentation. Most of the drugs analyzed for rate-dependent effects increased low rates of both punished and unpunished responding, while increasing higher rates less, or decreasing them; however, low rates of punished responding sometimes were increased more by pentobarbital, diazepam, and chlordiazepoxide than were matched rates of unpunished responding. In contrast, d-amphetamine and chlorpromazine usually increased low rates of unpunished responding more than matched rates of punished responding. These two drugs also decreased high rates of unpunished responding less than they decreased high rates of punished responding. Thus, the effects of drugs on punished responding depend on the control rate of punished responding; however, the rate-dependent effects of drugs on punished responding are not always the same as they are for unpunished responding.     

Persistent behaviour in extinction after partial deprivation in training

Four groups of rats were trained to run an alleyway with one trial per day. Two groups were always deprived when trained while the other two received a partial deprivation schedule. One group of each pair received a continuous reward in the goal box while the other received partial reward. A partial reinforcement effect was found during extinction. The partially deprived groups also showed persistence in extinction. This result extends parallels between the effects of satiation and nonreward upon behaviour.     

Effects of post-trial administration of naloxone and beta-endorphin on shock-induced fighting in rats

To study the involvement of endogenous opioid peptides in the development of shock-induced fighting, naloxone (2 mg/kg) or beta-endorphin (10 micrograms/kg) was administered subcutaneously immediately after the session and during nine consecutive daily sessions to rats repeatedly exposed to electric shocks. beta-Endorphin blocked the development of shock-induced fighting while naloxone facilitated it but only when shock-induced fighting occurred at a low rate. The effects of beta-endorphin were time dependent since when beta-endorphin was injected 90 min after the shock session instead of immediately after, its impairing effect disappeared. In addition, naloxone blocked the impairment produced by beta-endorphin. Differential postsession treatment of each member of pairs of rats with naloxone and beta-endorphin resulted in a higher probability of rats treated with naloxone to be dominant over rats treated with beta-endorphin in the test situation. These results are discussed in relation with the possible involvement of endogenous opioids in the modulation of the physiological consequences of defensive behavioral responses to shock.     

Effects of previous housing conditions on shock-induced aggression.

This study investigated shock-induced aggression as a function of housing rats in single or communal cages for varying periods of time before testing. Rates of fighting were unaffected by housing conditions when rats spent seven or 14 days in either of these settings before testing. Placing rats in these settings for 21 or 28 days before testing, however, did affect rates of fighting. Communal caging of subjects for 28 days before testing was particularly deleterious to shock-induced aggression. How rats are housed outside the experimental chamber is a variable affecting shock-induced aggression and should be considered both in designing future studies and as a topic for future investigation.     

Variable-ratio conditioning history produces high- and low-rate fixed-interval performance in rats

Four rats were exposed to an A-B-A-B series of 30 sessions each of variable-ratio 20 (A) and fixed-interval 30-s (B) schedules. Four other rats received 120 sessions of fixed-interval 30 s. The rats with a history of variable-ratio responding subsequently showed primarily high or low response-rate patterns on the fixed-interval schedule without evidence of classical scalloping (i.e., increased rates of responding throughout the interreinforcement interval), except infrequently in 1 rat. The rats exposed to only the fixed-interval 30-s schedule displayed the expected sequence of scalloping giving way to lower rate break-run or simply low-rate responding over time. This experiment shows that when naive rats are exposed to even a simple history of reinforcement (in this case, a variable-ratio 20), their subsequent fixed-interval performance is very different from comparable performance in naive rats, and might be said to be more similar to the responding of adult humans. The argument is made that care should be taken in comparing the fixed-interval performance of humans and nonhumans because humans have a complex history of reinforcement, whereas laboratory nonhumans are typically naive.     

Studies of wheel-running reinforcement: parameters of Herrnstein's (1970) response-strength equation vary with schedule order

Six male Wistar rats were exposed to different orders of reinforcement schedules to investigate if estimates from Herrnstein's (1970) single-operant matching law equation would vary systematically with schedule order. Reinforcement schedules were arranged in orders of increasing and decreasing reinforcement rate. Subsequently, all rats were exposed to a single reinforcement schedule within a session to determine within-session changes in responding. For each condition, the operant was lever pressing and the reinforcing consequence was the opportunity to run for 15 s. Estimates of k and R(O) were higher when reinforcement schedules were arranged in order of increasing reinforcement rate. Within a session on a single reinforcement schedule, response rates increased between the beginning and the end of a session. A positive correlation between the difference in parameters between schedule orders and the difference in response rates within a session suggests that the within-session change in response rates may be related to the difference in the asymptotes. These results call into question the validity of parameter estimates from Herrnstein's (1970) equation when reinforcer efficacy changes within a session.     

d-Amphetamine-chlorpromazine antagonism in a food reinforced operant

Dose effect curves for d-amphetamine and chlorpromazine were obtained with rats on a milk reinforced FR 10 schedule. A dose of d-amphetamine (2.5 mg/kg, i.p.) which completely suppressed all responding for 60 min was administered simultaneously (concomitant with the pretreatment times) with various doses of chlorpromazine. The d-amphetamine-induced cessation of responding was removed by several of the doses of chlorpromazine with maximal antagonism occurring at a dose of 1.5 mg/kg i.p. This dose of chlorpromazine, when administered independently, produced no observable side effects and showed no effect on the FR 10 schedule. One animal appeared to develop tolerance to the repeated dosages of d-amphetamine.     

A discrimination based on punishment

Twelve white rats learned to press a bar or lever when this act was intermittently followed by pellets of food. Once a stable rate of pressing had been established, the animals were subjected to electric shock as a punishment for each response during alternate five minute periods within the experimental session. A difference in rates during the safe and punished phases was manifested both by the experimental group (8 rats), who were provided with a light as a signal when it was safe to respond, and also, contrary to expectation, by the control group (4 rats), who continued in darkness throughout the session. The differential responding by the control group was greatly reduced, however, when the duration of each phase was reduced from five minutes to one.

The investigation was then continued to determine the role of some of the other factors in the situation. Increasing the severity of the shock increased the difference between the light and the dark rates. Withholding the pellets of food reduced the overall rates but did not affect the light-dark discrimination. Withholding the shock, on the other hand, permitted an increase in rate and caused the animals to lose their discrimination; when food had previously been withheld, however, so that the rate of response was relatively low, this deterioration in the discrimination was not as rapid as before. Restoration of the discrimination training under a lower hunger drive confirmed the finding that the formation of the discrimination was quite rapid and showed that the level of drive did not affect the proportionality between the rates in the light and in the darkness. These findings were interpreted by comparing the current procedure with those previously used in studies of avoidance reactions and conflict.     

Play fighting between kindling-prone (FAST) and kindling-resistant (SLOW) rats

Differences in the play behavior of 2 strains of rats suggest that different components of play fighting can be modified independently. The development of play fighting in cross-strain pairs of familiar and unfamiliar rats was examined to determine whether interacting with a non-congruent pair-mate would alter the pattern of play typical for each strain. In both strains, changes in play fighting were observed throughout development, but partner identity appeared to influence play fighting in different ways depending on age. These data suggest that some components of play may be more impervious to changes in social environment than other components.     

Reflexive fighting in the albino rat: Aggressive or defensive behavior?

Specific agonistic responses of albino rats were compared for dominant colony rats and intruders, and for rats in a “reflexive fighting” task. The “reflexive fighters” showed high levels of defensive responses such as boxing and freezing, and very low levels of aggressive behaviors such as piloerection, biting, and the lateral display. This pattern clearly suggests that the behaviors measured in the reflexive fighting task reflect conspecific defensive reactions, rather than “shockelicited aggression.” Moreover, striking responses seen in the reflexive fighting task also occur at a high rate when footshock is given to a solitary rat held in a boxing posture. Thus it appears that “reflexive fighting” primarily involves defensive rather than aggressive responses.     

Molar versus local reinforcement probability as determinants of stimulus value.

During one component of a multiple schedule, pigeons were trained on a discrete-trial concurrent variable-interval variable-interval schedule in which one alternative had a high scheduled rate of reinforcement and the other a low scheduled rate of reinforcement. When the choice proportion between the alternatives matched their respective relative reinforcement frequencies, the obtained probabilities of reinforcement (reinforcer per peck) were approximately equal. In alternate components of the multiple schedule, a single response alternative was presented with an intermediate scheduled rate of reinforcement. During probe trials, each alternative of the concurrent schedule was paired with the constant alternative. The stimulus correlated with the high reinforcement rate was preferred over that with the intermediate rate, whereas the stimulus correlated with the intermediate rate of reinforcement was preferred over that correlated with the low rate of reinforcement. Preference on probe tests was thus determined by the scheduled rate of reinforcement. Other subjects were presented all three alternatives individually, but with a distribution of trial frequency and reinforcement probability similar to that produced by the choice patterns of the original subjects. Here, preferences on probe tests were determined by the obtained probabilities of reinforcement. Comparison of the two sets of results indicates that the availability of a choice alternative, even when not responded to, affects the preference for that alternative. The results imply that models of choice that invoke only obtained probability of reinforcement as the controlling variable (e.g., melioration) are inadequate.     

Effects of chlorpromazine on fixed-ratio responding: modification by fixed-interval discriminative stimuli.

Effects of chlorpromazine (1 to 100 mg/kg) were assessed on two pigeons' responding under various modifications of a multiple schedule of food delivery. During a fixed-interval component, the first response after 5 min produced food; during the subsequent, fixed-ratio component, the 30th response produced food. Modifications of the schedule entailed changes in stimulus conditions imposed during the fixed-ratio component that did not systematically alter characteristics of performance under non-drug conditions. In the first phase of the experiment, distinctive visual stimuli were correlated with each schedule component (conventional multiple schedule); chlorpromazine produced small decreases in fixed-ratio responding (20% at 30 mg/kg). When each response during the fixed-ratio component produced the stimulus correlated with the fixed-interval schedule (fixed-interval discriminative stimulus) for 1.2 s, effects of chlorpromazine were not different from those under the conventional multiple schedule. Chlorpromazine produced greater decreases in fixed-ratio responding (55% at 30 mg/kg) when either the first response of each fixed ratio changed the stimulus correlated with the fixed-ratio schedule to the fixed-interval discriminative stimulus for the remainder of the fixed-ratio component, or when the fixed-interval discriminative stimulus was presented independently of responding according to a matched temporal sequence. When the fixed-interval discriminative stimulus was present continuously during the fixed-ratio component (mixed schedule), chlorpromazine produced even more substantial decreases in fixed-ratio responding (greater than 80% at 30 mg/kg). Effects of chlorpromazine on fixed-interval responding were also modified by the schedules of fixed-interval discriminative stimulus presentation. The effects of chlorpromazine were a joint function of the stimuli prevailing during the multiple schedule and the degree to which responding influenced these stimuli.     

Time-allocation matching between punishing situations

In the presence and absence of white noise, response-independent aversive events were delivered to rats according to several variable-time electric-shock schedules. The animals could switch from the noise component to the no-noise component and vice versa by making a single lever-press response. If the schedule in one component was not in operation when the animal was in the other component, the proportion of time allocated to one component equalled or matched the proportion of obtained punishers in the other component. If both schedules were always in operation, minimizing tended to occur: the animals allocated almost all of their time to the component having the lower shock rate. An analysis of these results, in terms of the expected time until an aversive event, is presented.     

PROMPTING TECHNIQUES TO INCREASE THE RETURN RATE OF MAILED QUESTIONNAIRES1

To increase the return rate of questionnaires mailed to clergy and physicians concerning their mental-health practices, different prompts were used after the questionnaire was received during four mail-outs to four randomly drawn samples of clergy and physicians. For each mail-out, the sample was divided into experimental (received prompt) and comparison (no prompt) groups, and one type of prompt or combination was used. Non-returnees of the questionnaire in the experimental group received either: (a) a single telephone call, (b) a memo, (c) a package (personal letter and new questionnaire) or package plus a telephone call, or (d) a double call. Comparison physicians and clergy were mailed only the original questionnaire. Relative to their respective comparison group's return rate, which averaged 22% across the four mail-outs (range 18% to 24%), the single call and package alone about doubled the overall return rate, the package and call increased the return rate about two-and-a-half fold, and the double call almost tripled the return rate. The memo was ineffective. A cost-effectiveness analysis indicated that the double-call procedure was less expensive than the single call, and much less expensive than the package alone or package with a call in securing returns. An analysis of the pattern of returns showed clearly that when prompts were not delivered (comparison groups), very few returns were received after about seven days from the initial mail-out. Most returns from prompts (experimental groups) were received by several days after the prompt. The results were seen as salient to the problem of reducing selection or volunteer bias in questionnaire studies and subsequent research demonstrating the effectiveness of telephone calls made about a week after distribution of surveys in securing high return rates was discussed.     

Visual Reinforcement Signals Interfere with the Effects of Reinforcer Magnitude Manipulations

Three experiments examined the effect of reinforcement magnitude on free-operant response rates. In Experiment 1, rats that received four food pellets responded faster than rats that received one pellet on a variable ratio 30 schedule. However, when the food hopper was illuminated during reinforcer delivery, there was no difference between the rates of response produced by the two magnitudes of reward. In Experiment 2, there was no difference in response rates emitted by rats receiving either one or four pellets of food as reward on a random interval (RI) 60-s schedule. In Experiment 3, rats responding on an RI 30-s schedule did so at a lower rate with four pellets as reinforcement than with one pellet. This effect was abolished by the illumination of the food hopper during reinforcement delivery. These results indicate that the influence of magnitude is obscured by manipulations which signal the delivery of reinforcement.     

Effects of promazine, chlorpromazine, d-amphetamine, and pentobarbital on treadle pressing by pigeons under a signalled shock-postponement schedule.

The effects of promazine on treadle pressing to postpone the presentation of electric shock were studied in three pigeons. The effects of chlorpromazine, d-amphetamine, and pentobarbital were studied in two of these pigeons. Each treadle press postponed electric shock for 20 sec and presentation of a preshock stimulus for 14 sec. Selected doses of both promazine and chlorpromazine increased the rates of treadle pressing in all birds. The response-rate increases produced by promazine and chlorpromazine were due to increased conditional probabilities of treadle pressing both before and during the preshock stimulus. d-Amphetamine (1 and 3 mg/kg) slightly increased responding in one of the birds, but not to the extent that promazine or chlorpromazine did. In the other bird, the 10 mg/kg dose of d-amphetamine increased shock rate but did not change response rate. Some doses of d-amphetamine increased the conditional probabilities of responding both in the absence of the preshock signal and during the preshock signal in both birds. Pentobarbital only decreased response rates and increased shock rates.     

The generality of learned helplessness in the rat

Two experiments were simultaneously conducted in which two different groups of 40 rats each were exposed to one of two different stressors. In both experiments half the subjects were pretreated with shock, half with underwater exposure. For each pretreatment stressor, half the subjects were allowed to escape, the other half were not. The experiments differed in the test task used. Approximately 24 hr after pretreatment, one-half the subjects from each pretreatment group received 20 water-escape trials in an underwater maze, the other half received 20 shock-escape trials in a two-way shuttle box. The subjects in each of the inescapable pretreatment conditions were slower to escape in the subsequent shock-escape and water-escape tasks when compared with subjects in the corresponding escapable pretreatment condition. The “learned helplessness” effect appeared to be no smaller when aversive stimuli were changed between pretreatment and test than when they remained the same.     

The biological function of Pavlovian conditioning: Learned inhibition of aggressive behavior in territorial fish

Following Pavlovian discrimination training, stimuli predicting the appearance of a territory intruder (an excitatory conditional stimulus, CS+) or the absence of that event (an inhibitory conditional stimulus, CS−) were presented to pairs of territorial male fish immediately before their first aggressive interaction. Pairmates that both received excitatory stimuli prior to the confrontation were significantly more aggressive than a control group which received the same training but which received neither a CS+ nor a CS− in the test. Pairmates in which both received a CS− were significantly less aggressive than the control group. In these three groups, no differences in aggression were observed between the individual members of a single pair. Two additional groups were composed of pairs whose members received different stimuli prior to the test. Although no differences were found between pairmates in the group in which one member received a pretest CS− while the other member received no stimulus presentation, large differences in aggressive behavior were obtained when one fish received a CS+ and its pairmate received a CS−. We discuss the behavioral ecology of terriorial behavior in fish and attempt to show the potential importance of these results in this naturalistic context. In addition, we discuss the implications of an ecological approach for causal analyses of inhibitory learning.     

Redundancy effects in the perception and memory of visual objects

Is visual representation of an object affected by whether surrounding objects are identical to it, different from it, or absent? To address this question, we tested perceptual priming, visual short-term, and long-term memory for objects presented in isolation or with other objects. Experiment 1 used a priming procedure, where the prime display contained a single face, four identical faces, or four different faces. Subjects identified the gender of a subsequent probe face that either matched or mismatched with one of the prime faces. Priming was stronger when the prime was four identical faces than when it was a single face or four different faces. Experiments 2 and 3 asked subjects to encode four different objects presented on four displays. Holding memory load constant, visual memory was better when each of the four displays contained four duplicates of a single object, than when each display contained a single object. These results suggest that an object's perceptual and memory representations are enhanced when presented with identical objects, revealing redundancy effects in visual processing.