Mediating factors in chick social pecking: 1. Effects of isolation,imprinting, and peer contact

Two experiments examined the influence of periods of social isolation on rates of intersubject pecking in pairs of domestic chicks. Of central interest was the effect of an imprinting condition wherein single birds were reared with either a red or green Styrofoam object. In the first experiment, imprinted subjects were given social pecking tests in the absence of the imprinting object, while in the second study the tests for social pecking were conducted in the presence of one of the imprinting objects. In the latter test the object was familiar to one bud of a pair, but was novel to the other animal. The results of both experiments showed that the rate of intersubject pecking of the imprinted subjects was intermediate to, and statistically different from both the low pecking rate of chicks reared in pairs and the high pecking rate of chicks reared in total isolation. The presence of a familiar object during tests in the second study seemed to serve as a secure base since chicks that had been reared with that object exhibited more social pecking than did chicks that were unfamiliar with the object. However, regardless of the provision of the object the social pecking of the imprinted chicks again fell on a point intermediate to the other groups. Hypotheses concerning a) intolerance of figureground movement and b) sheer stress of isolation were advanced to account for these results.     

Isolation-induced social pecking in domestic chicks: Contemporary correlates and sequelae

Aspects of the social pecking of domestic chicks in a free response situation were examined in a series of experiments. It was proposed that a dual pattern of responses involving (a) a preponderance of pecks at the head of a conspecific, and (b) heightened emotionality (as indicated by the emission of distress calls) might be taken to reflect an aggressive tendency, and evidence was reviewed that showed that a brief period of isolation was a sufficient condition to elicit such a pattern. The main questions asked in this paper are: (a) whether the gender of a chick had a material influence on the incidence of such social pecking, and (b) whether orders established in pecking exchanges reflected a unidimensional social ordering among chicks. In the 1st set of studies the effect of the sex of subject on rates of social pecking was tested. While an isolation procedure clearly produced the dual pattern of heightened head pecking and calling, reliable sex differences were not in evidence. In a 2nd study, concerned with the generality of social orders as observed in social pecking exchanges, the isolation procedure again was sufficient to produce apparently aggressive reactions but the resulting peck orders between chicks did not predict success in later tests when the same 2 subjects were pitted against one another in either approach or avoidance competitive tasks. These results are discussed in terms of the relationship of infant aggression to adult aggression, and suggestions are made for a revised view of the development of the aggressive behavior of fowl.     

Effects of sex,status, and mating cues on expected aggressive responses

The effect of sex, status, and mating cues on expected aggression was examined via three scenario‐based studies in which participants imagined themselves in a situation with a same‐sex instigator of a provocation. Participants were randomly assigned to receive a scenario, which included one of two levels of status of instigator (high, low), one of two levels of attractiveness of the instigator (unattractive, attractive), and one of two levels of provocation (apology, insult). Sex and dispositional aggressivity were also included in a full factorial design. Based on evolutionary psychology ideas, we anticipated that status and attractiveness would differentially influence expected aggression for men vs. women. Participants in Experiment 1 were instructed to imagine that they were alone, whereas participants in Experiments 2 and 3 imagined themselves in a situation that included mating‐related primes. In general expected aggression was greater for aggression‐prone participants and under conditions of provocation and/or a high‐status instigator. Experiments 2 and 3 found that, in the context of mate competition, sex differences in the effects of instigator provocation, status, and attractiveness emerged: greater aggressivity now only predicted more aggression for males but not females who were insulted; aggression was highest for females confronting an unattractive, high‐status instigator and for males confronting an attractive, high‐status instigator; females were more likely to aggress against a high‐status instigator, regardless of being in a steady relationship or a first date situation, but males were only more likely to aggress against a high‐status instigator in a first date situation. Aggr. Behav. 35:259–273, 2009. © 2009 Wiley‐Liss, Inc.     

Some characteristics of the aggressive behavior of mice after prolonged Isolation: Intraspecific and interspecific aspects

Experiments on mice have demonstrated changes in the relationships, interdependence and sequence of behavioral items following prolonged isolation. It was found that aggression in isolates was stereotyped and hardly amenable to the control not only by intraspecific but also by interspecific factors. Isolated mice, in contrast to the group-reared animals, spontaneously attacked adult rats. This finding was interpreted as being due to a disruption of behavioral plasticity under circumstances of prolonged isolation from conspecifics.     

The effects of urine on aggressive responses by male golden hamsters

Twenty adult male golden hamsters were isolated into individual cages for a period of six weeks, at the end of which time they had introduced into their home cages, on three occasions, a castrated male intruder. On each occasion the castrated intruder was daubed on the anogenital region with urine from one of three sources: (1) intact females, (2) other castrated males, and (3) intact males. Urine from a different source was applied to the castrated intruder on each of the three tests. Resident males consistently showed more aggression, sniffing, and following and less defensive behavior than the intruders. However, aggression by the resident males showed a significant variance over the three urine treatments given to the intruder. It is concluded that like male mouse urine, male hamster urine contains attack-provoking cues, but that unlike that of the mouse, female urine does not appear to be attack-inhibiting in this species.     

Effects of alpha and beta adrenergic antagonists on aggressive behavior in male mice

The effects of a variety of alpha and beta adrenergic antagonists were examined on the social encounters of isolated male mice with anosmic male partners. A range of alpha antagonists, including phentolamine, prazosin, and yohimbine, all suppressed social aggression. A range of beta antagonists, including propranolol, atenolol, metaprolol, and ICI 118, 551, also reduced this type of attack. Ethological assessment of the lowest effective dose of these adrenergic antagonists revealed a marked inhibitor action on offensive, social, and nonsocial behavior, while defensive responses and immobility were enhanced. It is concluded that the noradrenergic system has a significant non-specific role in mediating intermale aggression via both alpha and beta adrenergic receptor subtypes. © 1993 Wiley-Liss, Inc.     

Effects of social proximity on multiple aggressive behaviors

We systematically manipulated social proximity to examine its influence on multiple topographies of aggression. Aggression occurred at high levels during close-proximity sessions and at low levels during distant-proximity sessions even though social contact was presented continuously during both conditions. Topographies of aggression emerged sequentially across the close-proximity sessions, and all topographies were reduced to zero following extended sessions of this condition.     

Effects of alcohol intoxication and aggressivity on aggressive verbalizations during anger arousal

We examined the moderating effect of dispositional aggressivity on the relationship between alcohol intoxication and aggressive verbalizations. Using a laboratory anger-induction task that simulated an interpersonal conflict as a method to assess aggressive verbalizations (the articulated thoughts in simulated situations paradigm), 70 participants (33 women, 37 men) consumed either an alcoholic or a placebo beverage, and then imagined a series of audiorecorded interpersonal scenarios. Two blind-to-condition raters assessed the frequency of participants' aggressive verbalizations (insults, aggressive threats, belligerent provocations) articulated during anger arousal. Aggressivity was assessed using a standard measure of dispositional aggression. Results supported the aggressivity moderation hypothesis: intoxicated participants high in aggressivity responded with significantly more aggressive verbalizations relative to low-aggressivity participants regardless of beverage condition, and three times more aggressive verbalizations relative to the high-aggressivity/placebo group. There were no gender effects. These data support the hypothesis that alcohol potentiates aggression primarily among individuals at dispositional risk for engaging in such a behavior. Aggr. Behav. 34:428-436, 2008. (c) 2008 Wiley-Liss, Inc.     

Effects of pairing aggressive and nonaggressive children in strategic peer affiliation

Examined the behavior of 118 second graders who participated in a 6-week summer school program that incorporated strategic peer affiliation (a buddy system). Moderately aggressive children (the targets of the intervention) were paired with nonaggressive peers throughout the program. All participants were observed playing foosball with their buddies and with aggressive and nonaggressive nonbuddies as teammates. Aggressive children had lower levels of disruptive behavior when their teammate was nonaggressive, regardless of whether the teammate was a buddy. Nonaggressive children showed elevated disruptive behavior when playing with an aggressive nonbuddy, but not when playing with an aggressive buddy. The highest level of aggressive behavior was seen in pairs of aggressive teammates who were friends. One year later, no increase in peer-rated aggressive behavior was found in either group. Results suggest that unidirectional peer influence is possible and that strategic peer affiliation can be an effective intervention that does not put nonaggressive children at risk for acquiring undesired behaviors.     

Effects of reactivity to dorsal stimulation and social role on aggressive behavior in laboratory rats

Rats were selected on the basis of reactivity to dorsal tactile stimulation and then tested in a resident-intruder paradigm. While reactivity of residents did not influence the occurrence of agonistic behaviors or wounding of residents and intruders, reactivity of intruders did affect offensive and defensive patterns of interactions and the wounds sustained by residents and intruders. Subsequent to resident-intruder testing, rats were tested for shock-induced aggression. The pattern of the results and the results of additional experiments demonstrated that resident-intruder experience could affect subsequent shock-induced aggressive behavior.     

Effects of cohabitation with another female on aggressive behaviour in pregnant mice

Pregnant, nonpregnant (but mated) and virgin females were individually housed or lived with a pregnant or nonpregnant cagemate. They were subjected to a series of successive daily encounters with a male intruder, the cagemate being excluded. The most aggressive subjects were pregnant females living with a pregnant cagemate. Isolated pregnant females were as aggressive as pregnant females with a nonpregnant cagemate. Nonpregnant and virgin females were the least aggressive. Nevertheless nonpregnant subjects living with a pregnant cagemate generated higher aggressive scores than nonpregnant females living alone. The way in which a pregnant cagemate influences the aggressive behaviour of another pregnant or nonpregnant female is discussed.     

Effects of violent movies and trait hostility on hostile feelings and aggressive thoughts

The General Affective Aggression Model [Anderson CA, Deuser WE, DeNeve KM (1995): Personality and Social Psychology Bulletin 21:434–448; Anderson CA, Anderson KB, Deuser WE (1996): Personality and Social Psychology Bulletin 22:366–376] suggests that violent movies may increase aggression by increasing hostile feelings and the accessibility of aggressive thoughts. It also suggests that trait hostility may similarly influence affect and cognition. Experiment 1 explored the effects of viewing violent movie clips on affect and cognition. Participants who viewed a violent movie clip later reported higher levels of state hostility than did those who viewed a nonviolent clip. Experiment 2 added trait hostility to the design as a potentially important individual difference variable. The state hostility results of Experiment 1 were replicated. In addition, the relative accessibility of aggressive thoughts was increased by the violent clip, but only for low irritable participants. Discussion focused on the relevance to aggressive behavior. Aggr. Behav. 23:161–178, 1997. © 1997 Wiley-Liss, Inc.     

The ventromedial hypothalamus and aggressive behaviour in rats

Male rats were given bilateral lesions in either the anterior or posterior ventromedial hypothalamus (VMH). The intermale aggressive behaviour of these animals within their own territory was observed before and after the surgical procedure and compared with the behaviour of sham-operated animals. The effects of anterior VMH lesions include an increased tendency to respond with frontal threatening upon approach of a conspecific male. This behaviour closely resembles the aggressive responses described in “shock-induced aggression” tests. Posterior VMH lesions facilitate territorial aggressive behaviour characterized by approaching the opponent followed by lateral threatening and fighting. It is suggested that 2 distinct neural substrates exist, which serve to inhibit defensive (anterior-VMH) and offensive (posterior-VMH) intermale aggression, respectively.     

Effects of response requirement and alcohol on human aggressive responding.

Nine men participated in two experiments to determine the effects of increased response requirement and alcohol administration on free-operant aggressive responding. Two response buttons (A and B) were available. Pressing Button A was maintained by a fixed-ratio 100 schedule of point presentation. Subjects were instructed that completion of each fixed-ratio 10 on Button B resulted in the subtraction of a point from a fictitious second subject. Button B presses were defined as aggressive because they ostensibly resulted in the presentation of an aversive stimulus to another person. Aggressive responses were engendered by a random-time schedule of point loss and were maintained by initiation of intervals free of point loss. Instructions attributed these point losses to Button B presses of the fictitious other subject. In Experiment 1, increasing the ratio requirement on Button B decreased the number of ratios completed in 4 of 5 subjects. In Experiment 2, the effects of placebo and three alcohol doses (0.125, 0.25, and 0.375 g/kg) were determined when Button B presses were maintained at ratio values of 20, 40 and 80. Three subjects who reduced aggressive responding with increasing fixed-ratio values reduced aggressive responding further at higher alcohol doses. One subject who did not reduce aggressive responding with increasing fixed-ratio values increased aggressive responding at the highest alcohol dose. The results of this study support suggestions that alcohol alters aggressive behavior by reducing the control of competing contingencies.     

Gender differences in emotional and overt/covert aggressive responses to stress

We examined the role of stress exposure on gender differences in hostile (emotional and behavioral) reactions within the context of a laboratory paradigm. Aggressive behavior was indexed via the intensity (overt) and the duration (covert) of putative shocks delivered to a confederate. Half of the participants were exposed to a chronic stressor (high stress) and half were not (low stress). Participants' emotional responses were measured via self-report mood ratings before and after the experiment. Men displayed higher aggression in both stress conditions, which corresponded to their ratings of state hostility. On the other hand, women in high stress delivered lower intensity shocks, and this decreased overt aggression was positively correlated with sadness ratings. However, women did not decrease their levels of shock duration (covert aggression) under high stress and showed equivalent shock duration compared with men in high stress. These findings are discussed in terms of differential overt manifestations of distress between men and women.     

Aggressive reactions of ducklings to a nonliving target object

This study asked whether ducklings' forceful pecks at a nonliving target object could be validly identified as aggressive. Previously isolated ducklings were exposed to a small cylindrical object that could serve as a target for aggressive pecks and as an object for attachment. After initially attempting to flee from the target, they vigorously pecked at it and also showed signs of the formation of a social (imprinting) attachment. In all important respects this pattern of behavior was identical to the pattern of escape, aggressive pecks, and attachment seen when a previously isolated duckling first encounters a conspecific. Social housing, a manipulation which attenuates aggression against live targets in ducklings and other species, reduced pecking at the nonliving target object. Early aversive stimulation, which enhances aggression against live targets, increased pecking at the object. These findings support the use of nonliving targets in the study of aggression in ducklings.     

Influence of timing of post-weaning isolation on play fighting and serious aggression in the male golden hamster (Mesocricetus auratus)

Effects of timing of social isolation on play fighting and serious fighting were studied at different ages in male golden hamsters. Litters were isolated at 21, 35, and 65 days of age, and tested in a resident-intruder paradigm. Behaviors were compared within grous and with a fourth group of socially reared conspecifics. The earlier the pups were isolated, the more they engaged in play activities. Later, in adulthood, the aggression level of the same animals was retested using the same paradigm. The three isolated groups showed a high level of aggression, with significant differences among them. When compared with socially reared subjects, a reliable difference in the level of aggression was also found. These results support the view that early social experience is important, suggesting that isolation during early critical periods of socialization has a significant impact on play fighting, whereas short periods of isolation may be enough to trigger adult agonistic behavior. © 1994 Wiley-Liss, Inc.     

Human aggressive responses maintained by avoidance or escape from point loss.

During 50-min sessions, 6 male human subjects could press either Button A or Button B available as nonreversible options. Button A presses were nonaggressive responses and earned points according to a fixed-ratio 100 schedule. Prior to the experiment subjects were instructed that every 10 (fixed-ratio 10) Button B presses (aggressive responses) subtracted a point from a fictitious 2nd subject. A random-time schedule of point loss was used to engender aggressive responding. The instructions attributed these point losses to the Button B presses of the subject's fictitious partner. Aggressive responding either escaped or avoided point loss by initiating an interval free of point loss. The duration of the interval was varied systematically across sessions. Avoidance contingencies maintained a high rate of aggressive responding over 30 sessions in the absence of point loss. Escape contingencies also maintained aggressive responding across sessions, with rates of aggressive responding corresponding to rates of point loss.