Multitrial inhibitory avoidance learning in the crab Chasmagnathus.

Chasmagnathus crabs placed in the dark compartment (DC) of a double-chamber device and given electrical shocks whenever they entered or remained in the light compartment (LC), showed an LC-avoidance behavior when tested 24 h after a training session of three 30-min periods with 60-min intervals. The avoidance behavior depended neither on the shock number nor on the distribution at training but only on exposure to the LC-shock contingency, thus suggesting that crabs learn to associate the LC with an aversive situation. The learning outcome disclosed a higher degree of refraining from entering the LC rather than a faster escaping to the DC. Distributed practice proved more effective on crab avoidance learning than massive practice. Retention of the learned behavior occurred after a 24-h rest interval in an environment different from that of the training apparatus. Experimental devices previously used in avoidance learning studies with crabs were improved here by automating both the computation of latency values and the event recording.     

Long-lasting and context-specific freezing preference is acquired after spaced repeated presentations of a danger stimulus in the crab Chasmagnathus

A visual danger stimulus elicits an escape response in the crab Chasmagnathus that declines after repeated presentations. Previous results report that such waning may be retained as context-signal memory (CSM) or signal memory (SM): CSM is long lasting, associative, and produced by spaced training, while SM is an intermediate memory, nonassociative, and produced by massed training. The performances of both spaced and massed trained crabs are here examined, using video analysis to determine topographic changes in the behavioral response during and after training. During spaced training, escape vanishes and is mainly replaced by freezing, while during massed training, escape decreases over trials without being replaced by any defensive response. After 24 h, the marked proclivity to freezing persists in spaced trained crabs, while a high level of escaping is shown by massed trained crabs. The long-lasting freezing preference of spaced trained crabs proves to be context-specific and apparent from the very first presentation of the danger stimulus at testing, though freezing is not triggered by the sole exposure to the context. We conclude (a) that freezing preference is the acquired response of the CSM process; (b) that CSM can be properly categorized as an instance of contextual conditioning and SM of classical habituation; (c) that CSM and SM are not two phases of a memory processing but two distinctly types of memory; and (d) that therefore, the temporal distribution of training trials has a drastic effect on crab's memory, more dramatic than that previously described. The possibility that massed and spaced presentations of the same stimulus may represent two different stimulus types is discussed.     

The generality of outside-in processing routines in the analysis of form

In a previous study, Earhard and Walker (1985) showed that outer details of forms were more accurately reported than inner details. Although they suggested that this pattern might reflect a routinely applied outside-in processing strategy, their ability to generalize was limited by a reliance on small, single forms which occupied a fixed position in the visual field. To provide a more adequate assessment of generality of outside-in processing, a series of five experiments examined the discriminability of inner- and outer-line detail under a wide variety of conditions. Support for a general outside-in processing routine was obtained. More accurate reporting of outer detail was evident with large as well as small forms, with long and short exposure durations, and with trial-by-trial variations in the size and orientation of forms. Outer lines were also reported more accurately when a number of forms were presented simultaneously for inspection and under circumstances where error rates were low and reaction time procedures were employed. Evidence was presented to support the view that the more accurate discrimination of outer detail reflected the deployment of an attentional strategy.     

Retrieval improvement is induced by water shortage through angiotensin II

Angiotensin II (ANGII) has an evolutionary preserved role in determining adaptative responses to water-shortages. In addition, it has been shown to modulate diverse phases of memory. Still, it is not clear whether ANGII improves or spoils memory. We demonstrated that endogenous angiotensins enhance consolidation of a long-term associative memory in the crab Chasmagnathus and that water shortage improves memory consolidation through brain ANGII actions. Here, we show that weakly trained crabs, when water-deprived, exhibit enhanced retrieval. Subsequently, memory retention is indistinguishable from that of strongly trained crabs. ANGII, but not angiotensin IV, is a necessary and sufficient condition for such enhancing effect. We conclude that ANGII released due to water shortage leads to enhanced memory retrieval. Thus, it seems that ANGII has an evolutionary preserved role as a multifunction coordinator that enables an adaptative response to water-shortage. The facilitation of memory consolidation and retrieval would be among those coordinated functions.     

Force and dominance in the agonistic behavior of the freshwater crab Potamon fluviatile

In decapods, no analysis has ever been conducted of the force exerted by chelae, and the role that strength plays in the establishment of hierarchies. For this purpose, a device was designed to measure the force produced by the major chela in the freshwater crab Potamon fluviatile, where dominance hierarchy and agonistic behavioral patterns have previously been analyzed. Experiments showed that only in the females is strength the main factor influencing the outcome of contests. In males chela size more than chela strength is used to settle conflicts, together with other nonphysiognomic characteristics, molding the aggressive state of one individual, such as its history, including isolation from conspecifics, and possibly hormone concentration and metabolic levels.     

The Effects of Prosocial and Aggressive Videogames on Children's Donating and Helping

We investigated the effects of a prosocial and an aggressive videogame on children's prosocial behavior. Third-, fourth-, seventh-, and eighth-grade boys and girls (N = 160) were randomly assigned to either a control condition or one of four treatment conditions. In two of the treatment conditions, children played a videogame with prosocial content either singly or cooperatively with another child. In the other two conditions, children played an aggressive videogame either singly or competitively. Subsequent levels of donating and helping were measured. A three-way analysis of variance indicated that older students donated significantly more than did younger students. Children who played either of the aggressive videogames donated significantly less than did those who played prosocial games by themselves. No significant effects were found for helping. Playing the prosocial videogame did not increase prosocial responding, but playing the aggressive videogame tended to suppress this behavior. The failure of the prosocial game to accelerate prosocial responding might be due to the relatively brief treatments used in this study and/or to the particular prosocial videogame utilized.     

Aggressiveness and memory: subordinate crabs present higher memory ability than dominants after an agonistic experience

A relationship between aggressiveness and memory has been proposed in several studies with different animal species. Here, we study this possibility in the crab Chasmagnathus granulatus, using the context-signal memory model (CSM) that involves an association between the learning context and a visual danger stimulus. Each experiment consisted of an agonistic phase and a memory one. During the former, matched pairs of male crabs were staged in two 10-min encounters and the dominant or subordinate condition of each member of the dyad was determined. During the memory phase, crabs were trained to acquire CSM and tested 24 h later. Results showed that the agonistic encounter, staged 48 h before the acquisition of CSM, can modulate memory according to the dominance condition of the fighter; in such a way that memory retention of subordinates results higher than that of dominants. By contrast, when the memory phase preceded the agonist one, forthcoming dominants and subordinates did not differ in their memory ability. The memory modulation would not be linked to a dominance status but to a persistent dominance relationship fully reconstructed in each encounter between the same opponents. Therefore, the crab's CSM would not depend directly on predetermined intrinsic properties, but on the outcome of the fight, which would be determined in turn by the relative aggressiveness of the fighters. The finding that the agonistic episode modulates memory opens the possibility of using this episodic interference to probe the function of diverse phases of CSM.     

Grooming expresses harderian gland materials in the blind mole rat

The blind mole rat (Spalax ehrenbergi) is a highly aggressive and solitary rodent that shows the most striking physiological and behavioral adaptations to underground life. The eyes are not detectable externally; they are atrophied and covered by a thick layer of skin. A considerable part of the orbit is occupied by a very large Harderian gland. The current study demonstrates that during autogrooming the mole rat expresses Harderian gland materials from the conjunctival sac to the external nares and spreads them onto the fur. In contrast to other rodents, the mole rat's grooming behavior is usually confined to the front part of the body and does not progress after the head wipes to ventrolateral torso licking. Moreover, in highly aggressive encounters grooming sometimes ceases after the second phase-the nose wipe bouts. The unique first phase of the mole rat's grooming consists of highly rapid strokes over the skinny border of the head, which we assume help to squeeze Harderian materials from the gland. Unlike other rodents, in which grooming occupies a considerable part of their waking time, mole rats, cage individually, rarely perform autogrooming behavior. Grooming in mole rats has been found to be highly correlated with aggressive encounters, and submissive animals exhibit significantly more grooming than their dominant opponents. It is speculated that the Harderian gland discharge may serve as an appeasing substance when mole rats meet to reduce the extreme aggressiveness typical of these subterranean rodents. © 1995 Wiley-Liss, Inc.     

Rapid contact call-driven induction of NR2A and NR2B NMDA subunit mRNAs in the auditory thalamus of the budgerigar (Melopsittacus undulatus)

In situ hybridization histochemistry was used to assess the effect of auditory stimulation with natural contact calls on expression of NR2A and NR2B NMDA subunit mRNAs in neurons of the thalamic auditory relay nucleus ovoidalis (Ov) of a vocal learning parrot species, the budgerigar (Melopsittacus undulatus). The results showed that both the core (Ov) and ventromedial shell subdivisions (Ovm) of ovoidalis contained neurons expressing NR2A and NR2B mRNA in no-stimulation control subjects and that the distributions of neurons expressing these subunit mRNAs were very similar in both the core and shell of Ov. Contact call stimulation (5, 30 and 180 min) resulted in substantial increases of 50-60% in the number of neurons expressing NR2A and NR2B mRNAs in both the core and shell. Staining intensity, as measured by the optical density of stained somata approximately doubled compared to controls for both NR2 subunits in the 5 and 30 min conditions, but declined from 30 to 180 min. In all conditions, the density, but not staining intensity, of neurons expressing NR2B exceeded NR2A expression. Furthermore, the density of neurons expressing both subunit mRNAs in call stimulation conditions was greater in the core than in the shell despite the fact that total neuronal density was approximately 20% higher in the shell. Previous experiments have shown that call stimulation is more effective at inducing expression of the immediate early gene zenk in the Ov shell than core; however the present results do not indicate that either NR2A or NR2B mRNA expression mediates this effect since neither subunit exhibits greater expression in Ovm. Ca(++) release is needed for immediate early gene expression, however and, notably, Ovm contains large numbers of neurons containing CGRP, a peptide which has been shown to increase cytosolic Ca(++) levels.     

催化剂模型:媒体暴力真的可以预测社会暴力?

国内研究者熟知的一般攻击模型认为,媒体暴力与社会暴力之间存在"因果关系"。2008年,Ferguson针锋相对地提出了催化剂模型,认为媒体暴力与社会暴力之间是"零因果"的关系,媒体暴力只是扮演着犯罪行为的文体催化剂,而不是犯罪行为的触发器。首先,介绍了催化剂模型的理论观点和近年来相关的支持性实证研究;其次,分析了催化剂模型对一般攻击模型所持观点的种种质疑;最后,总结了该领域的研究困境和未来研究的方向。     

Aggression-consistent, -inconsistent,and -irrelevant priming effects on selective exposure to media violence

Priming with aggressive concepts increases males' attraction to media violence. It was hypothesized that priming with schema-irrelevant concepts would decrease interest relative to the effects of schema-relevant concepts, whether or not the schema-relevant concepts were also schema-consistent. Thirty male undergraduates used lists including aggressive (schema-consistent and schema-relevant), positive or prosocial (schema-inconsistent yet relevant), or entirely neutral (schema-irrelevant) words to write short stories (priming task), then received an opportunity to select videotaped film clips for viewing. Subjects primed by aggressive word lists included more aggression, anger, fear, and violence in their stories than did those in the aggression-inconsistent and aggression-irrelevant conditions, whereas aggression-inconsistent priming yielded more fun, helping, and joy than did other conditions. Aggressively primed subjects expressed more interest in films containing violence and hostility than did neutrally primed subjects, whereas aggression-inconsistent priming did not differ significantly from either aggressive (schema-consistent) or neutral (schema-irrelevant) priming. Findings indicate that the aggressive priming activates aggressive concepts that make violence and hostility more salient to individuals. Because male undergraduates typically express interest in violence, enhanced salience leads to increased interest. © 1992 Wiley-Liss, Inc.     

Class size,pupil attentiveness and peer relations

Background: Despite a long‐running debate over the effects of class size differences on educational performance there is little evidence on the classroom processes that might be involved. Aims: The effects of class size differences are examined in relation to social and behavioural adjustment to school, in terms of two dimensions: attentiveness and peer relations. It was predicted that as class size increased there would be more inattentiveness in class and more signs of social difficulties between children in the form of more rejection, asocial, anxious and aggressive behaviour, and less prosocial behaviour. Samples: Data came from a large‐scale longitudinal study of children over KS1 (4‐7 years). The observation study was based on a subsample of 235 children in 21 small (average 19 children) and 18 large (average 33 children) reception classes (aged 5 years). The PBR sample involved over 5,000. Methods: There were two complementary methods of data collection: first, a systematic observation study of pre‐selected target children in terms of three ‘social modes’ — when with their teachers, other children and when not interacting — and in terms of work, procedural, social and off‐task activities; and, second, a teacher administered Pupil Behaviour Rating (PBR) scale comprising over 50 items rated on a 3‐point scale grouped into six ‘factors’: hyperactive/distractible, aggressive, anxious/fearful, prosocial, asocial, and excluded. Results: Observations showed that children in large classes were more likely to show off‐task behaviour of all kinds, and more likely to interact with their peers in terms of off‐task behaviour, social, and also on‐task behaviours. Connections between class size and PBR factors were not strong. There was no support for the view that peer relations are better in smaller classes; indeed, there was a slight tendency for worse peer relations, in terms of aggression, asocial and excluded, in the smallest classes. Conclusions: There was confirmation that children in large classes are more distracted from work and more often off task. The unexpected result, based on teacher ratings, that small classes may lead to less social and more aggressive relations between children is discussed, along with implications for teachers of a tendency for more peer‐related contacts in large classes.     

Behavioral and neuronal attributes of short- and long-term habituation in the crab Chasmagnathus

Investigations using invertebrate species have led to a considerable progress in our understanding of the mechanisms underlying learning and memory. In this review we describe the main behavioral and neuronal findings obtained by studying the habituation of the escape response to a visual danger stimulus in the crab Chasmagnathus granulatus. Massed training with brief intertrial intervals lead to a rapid reduction of the escape response that recovers after a short term. Conversely, few trials of spaced training renders a slower escape reduction that endures for many days. As predicted by Wagner’s associative theory of habituation, long-term habituation in the crab proved to be determined by an association between the contextual environment of the training and the unconditioned stimulus. By performing intracellular recordings in the brain of the intact animal at the same time it was learning, we identified a group of neurons that remarkably reflects the short- and long-term behavioral changes. Thus, the visual memory abilities of crabs, their relatively simple and accessible nervous system, and the recording stability that can be achieved with their neurons provide an opportunity for uncovering neurophysiological and molecular events that occur in identifiable neurons during learning.     

Fixed-ratio pausing: Joint effects of past reinforcer magnitude and stimuli correlated with upcoming magnitude

Pigeons responded on fixed-ratio schedules ending in small or large reinforcers (grain presentations of different duration) interspersed within each session. In mixed-schedule conditions, the response key was lit with a single color throughout the session, and pausing was directly related to the past reinforcer (longer pauses after large reinforcers than after small ones). In multiple-schedule conditions, different colors accompanied the ratios ending in small and large reinforcers, and pausing was affected by the upcoming reinforcer as well as the past one. Pauses were shorter before large reinforcers than before small ones, but they continued to be longer after large reinforcers than after small ones. The influence of the past reinforcer was modulated by the magnitude of the upcoming reinforcer; in the presence of the stimulus before the small reinforcer, the effect of the past reinforcer was enhanced relative to its effect in the stimulus before the large reinforcer. These results show that pausing between ratios is jointly determined by two competing factors: past conditions of reinforcement and stimuli correlated with upcoming conditions.     

Identification with film characters, covert aggressive verbalization, and reactions to film violence

To determine some conditions governing the aggressive aftereffects of identification with aggressive film characters, men were first angered by a confederate and then exposed to a film clip of a violent boxing match. Subjects instructed to identify with the winner of the prize-fight were subsequently more aggressive toward the confederate than subjects instructed to identify with the loser or subjects not asked to identify with a film aggressor. Apparently, viewers must perceive their identificand incur reinforcement for his aggression before they become more aggressive themselves. However, requiring subjects to make implicit aggressive verbalizations during the film completely eliminated any aggressive aftereffects of identification. This finding was opposite to prediction and suggested that covert verbalization interfered with subjects' ability to make the vicarious aggressive responses which mediate increased subsequent aggression.     

Social inference and individual differences in aggression: Evidence for spontaneous judgments of hostility

This research examined the hypothesis that aggressive vs. nonaggressive individuals differ in their spontaneous trait inferences, i. e., inferences made without any conscious intention of inferring characteristics of an actor. We anticipated that spontaneous processing conditions would be more revealing of aggressive/nonaggressive differences than would conditions that prompt deliberate inference processes. We used a cued-recall paradigm. Aggressive and nonaggressive subjects were instructed to memorize sentences that were open to either hostile or nonhostile interpretations. Sentence recall was then cued by either hostile dispositional terms or by words that were linked semantically to the element of the sentences. Within the spontaneous inference condition, semantic cues prompted twice as much recall as hostile cues among nonaggressive subjects, whereas dispositional cues aided recall more than semantic cues among aggressive subjects. As predicted, within the delinerate inference conditions there were no aggressive/nonaggressive differences. The nature of spontaneous vs. deliberate inferential processes and the advantages of spontaneous inference paradigms for testing predictions about schema-based processing in aggression are discussed. © 1995 Wiley-Liss, Inc.     

Effect of naloxone pretreatment on habituation in the crab Chasmagnathus granulatus

On sudden presentation of a passing shadow, the crab Chasmagnathus granulatus reacts with an escape response that habituates after repeating the same stimulus. In a first series of experiments, a range of naloxone (NX) doses (0.8, 2.4, 3.2, and 6.2 micrograms/g) was injected into crabs 15 min before one 15-trial habituation session. An enhancing effect of 3.2 micrograms NX/g on responsiveness appeared over trials, that cannot be explained either by a ceiling effect or by a delay in peak drug action. Two doses below 3.2 microgram/g and one dose above had no significant effect. Results from a second series of experiments showed that the 3.2 microgram NX/g effect vanishes after 15 trials (1 h after injection). The hypothesis that crab's habituation involves the action of an endogenous opioid mechanism is put forward to account for the naloxone pretreatment effect.     

Flicker Induction and the Role of Molar Properties in the Critical Flicker Frequency

This experiment investigated the effects of peer vs. adult frustration on aggressive responses of eight-year-old boys. In addition, the effect of frustration vs. nonfrustration on aggressive responding was tested.

In two experimental conditions, groups of four boys were brought into a room and read instructions preparing them for a game-competition situation. Either a peer or an adult confederate disrupted the group's goal completion. A control condition without disruption was also used.

Considerably more aggression was expressed in the peer condition than in the adult condition, on the basis of the aggression category of the Rosenzweig Picture-Frustration Test, Children's Form (20). Frustration in general led to significantly more aggression than no frustration.

The results indicated that boys of middle childhood are more attentive to and are likely to exhibit more aggressive reaction to peer frustration than adult frustration. In addition, frustration in general yielded more aggressive reaction than no frustration, supporting the original frustration-aggression theory proposed by Dollard et al. (8).     

Aggression is suppressed by acute stress but induced by chronic stress: Immobilization effects on aggression, hormones, and cortical 5-HT1B/ striatal dopamine D2 receptor density

Although it has been established by a number of investigators that a variety of stressors are associated with the induction of aggressive behavior, two specific issues remain unanswered. First, it is unclear whether the contexts surrounding stressors (e.g., stressor length and chance of winning over opponents) change outcomes regarding aggressive behavior. Second, if a relationship exists between stress and aggressive behavior, altered levels of stress-related hormone (e.g., corticosterone [CORT]), as well as aggression-related biomarkers (e.g., testosterone [T], density of prefronto-cortical 5-HT(1B) receptor and striatal dopamine D(2) receptor [D2r]) may contribute to changes in aggressive behavior. Thus, we examined how immobilization (with a 1-, 5-, or 10-day exposure) would impact (1) a longitudinal course of aggression toward different-sized opponents, (2) levels of CORT and T, and (3) densities of 5-HT(1B) receptor (5-HT1Br) in the prefrontal cortex (PFC) and D2r in the striatum. It was found that, regardless of small or large opponents, a single 2-h exposure to immobilization reduced aggressive behavior (stress-suppressed aggression) over time, whereas repeated (10-day) exposure to immobilization escalated aggressive behavior (stress-induced aggression). These stress effects persisted up to 1 week of recovery from immobilization stress. Moreover, immobilized rats demonstrated elevated levels of T, but not CORT, as compared with controls. Finally, acute immobilization altered D2r densities in the shell of the nucleus accumbens, and chronic immobilization changed 5-HT1Br in the PFC, including the downregulation of 5-HT1Br densities in the right prelimbic and orbitolateral cortices. The potential relationships among stress, aggression, and 5-HT1Br/D2r roles are discussed.     

Watching Aggressive, Attractive, Female Protagonists Shapes Gender Roles for Women Among Male and Female Undergraduate Viewers

The impact of exposure to media representations of aggressive, attractive, female protagonists on audiences?? gender role expectations for women was explored through a laboratory experiment with 122 undergraduates from a large university on the west coast of the United States. Participants viewed a segment of a major Hollywood motion picture that featured a female protagonist who was either highly attractive or less attractive and either highly aggressive or not aggressive. Viewing clips featuring a female protagonist who was both aggressive and stereotypically attractive led to greater endorsement of stereotypically feminine and stereotypically masculine gender role expectations for women. The effect on endorsement of stereotypically masculine expectations was partially mediated by the perception that the protagonist was a good role model for women. Although women endorsed both feminine and masculine gender role expectations for women more strongly than men, the effects of exposure to aggressive, attractive, female protagonists were similar for both male and female participants. Results are discussed in terms of gender stereotype activation and superwoman expectations for women.