Aggressive action is behaviour aimed at causing either physical or psychological pain. - Aronson et al, 1997

As aggression is an emotional reaction and it is very hard to measure. The most common way aggression is measured in lab studies is by asking people to give electric shocks. Other ways include getting them to punch a doll, to verbally rate how aggressive they felt, or to push a button to rate their aggression on a scale. However, these are subjective and people have different perspectives of aggression.

There are many theories as to what causes us to act aggressively.

Frustration-aggression Hypothesis

When we are blocked from achieving our goal, this leads to frustration. Frustration can then lead to aggression. However, sometimes this frustration can be displaced and lead to something else, eg depression.

Frustration can be increased when it is unexpected, or when we are nearer to our goal when it is blocked - you are more likely to get angry at someone for pushing in front of you if you are second in a queue than if you are 50th in the queue. Frustration is likely to be less keenly felt when it is understandable, legitimate or unintentional.

Relative Deprivation Theory

When people feel that they deserve more than they have got, this can lead to frustration, which can then lead to aggression. This does not always happen in the poorest areas, as you might expect, as it is about what people feel they deserve. It occurs when people compare what they have to what others around them have. It often occurs when conditions are improving and expectations are rising but are not met.

Cue-arousal Theory

According to this theory, although frustration leads to anger, it doesn't necessarily lead to aggression. There needs to be some associated stimulus to spark the aggression. For example, if you were carrying a pile of heavy books and couldn't get the door open, this would cause you to feel frustration, but not aggression. However, if someone then laughed at you, this may be the cue to aggression.

This was shown by an experiment called the Weapons Effect. Participants were given a task to do and were verbally criticised for their performance of the task, leading to frustration. They were then given the chance to give electric shocks to the people who had criticised them. Half of the participants did this while there was a gun present. These people gave significantly more shocks than the other half, suggesting that the gun acted as a cue to aggression. However, one criticism of this study is that there may be cultural differences. For example, some people may have given less shocks as the other person had the gun.

Excitation-transfer Theory

This theory suggests that arousal from one situation can be transferred to another situation. For example, a number of participants were provoked by verbal abuse. Half then went and did some exercise and half did nothing. All of the participants then had the chance to give electric shocks to the people that had abused them. The people that did the exercise gave more shocks than the others. This showed that the arousal from the exercise was transferred into aggression.

The Excitation-transfer theory was criticised for assuming that aggressive acts are committed without thinking, which does not account for acts that are planned in a cold, calculating way. It was later revised to include cognitive processes. When we attribute the frustration to a person, we are more likely to feel aggression. When we attribute the frustration to the situation, we are less likely to feel aggression.

Social Learning Theory

If a child is rewarded for being aggressive that behaviour is positively reinforced and is more likely to be repeated. For example, a child hits another child and the second child gives up his toy. The first child has been rewarded for her violent behaviour, so will probably be violent again in the future.

Similarly, a child may be rewarded for aggressiveness through negative reinforcement. This means that something bad is avoided. For example, a child prevents another child from stealing his toy by threatening her and he gets to keep the toy. Again, the aggressive behaviour is rewarded and the behaviour is likely to be repeated.

When children watch others being rewarded for aggressive behaviour, they are likely to learn this behaviour through vicarious reinforcement. For example, a psychologist called Bandura did an experiment with five groups of children. The first group were shown a video where an adult behaved violently towards a bo-bo doll¹ and being rewarded for this behaviour. The second group were shown a video with an adult being punished for violent behaviour towards the doll. The third group were shown a cartoon cat behaving violently. The fourth group were shown a non-violent video and the fifth group were not shown a video at all. All of the children were then allowed to play in a room full of toys which included bo-bo dolls. Bandura found that all of the children who saw the violent behaviour on the films acted twice as aggressively towards the bo-bo dolls than the control groups. However, there was no difference between these groups.

There are, however, several criticisms of this research. Some people argued that this was not a good example of aggression as no humans were hurt. Also, the bo-bo dolls are designed to be punched so they invite aggression. The ecological validity of the experiment was low. This means it is difficult to generalise the findings to real life as the experiment was done in a lab and this is not very realistic. Another criticism is that the children that acted aggressively in the experiment tended to be the ones who were rated as aggressive anyway.

Deindividuation

When people are in a large group or crowd, they tend to lose a sense of their individual identity and take on the identity of the group. This can make them commit acts of aggression and violence that they wouldn't normally commit. They do not take responsibility for these acts. A good example is that of football hooliganism. There are two factors involved with this:

• Public self-awareness - This is an individual's sense that others are aware of them and that they are identifiable to others.
• Private self-awareness - This is the individual's own sense of awareness of himself, his thoughts, actions, beliefs, etc.

Both of these factors decrease in deindividuation.

An experiment was done to investigate this. A group of female participants were dressed in dark clothes with hoods. They were never called by name and they were placed in a dim room. The second group were wearing regular clothes and large name badges. They were in a brightly-lit room. When asked to give electric shocks as part of a 'learning experiment', the first group gave twice as many as the second group.

Other evidence comes from a researcher who looked at several newspaper articles about mob attacks. He found that the larger the mob, the more violent, savage and prolonged the attacks were.

Environmental Stressors

Studies have found that many environmental factors increase aggression.

Temperature

When the temperature rises people tend to feel more disposed to aggressive behaviour. A researcher looked at incidents of violence across the USA and the corresponding weather reports. He found that when it was moderately hot (84°F) there was the most violence, but after weather higher than this temperature, the violence decreased. This was backed up by a lab study by Baron and Bell who put participants in rooms of different temperatures then increased the heat in each of the rooms. The participants were asked to give electric shocks. They found that as the temperature rose, the participants gave more electric shocks, but that once the temperatures got to extreme levels, the shocks decreased.

However, another researcher called Anderson looked at cases of violent acts including rape, murder and assault. He found that there was a steady increase as the temperature rose but that there was no indication of decline in extreme heat.

One problem with this theory is that it would probably not be true to say that people in hotter countries are more aggressive.

Crowding

A higher density of people leads to higher levels of aggression. This theory links to deindividuation (see above). It is also unpleasant when your personal space is invaded. For example, there is the most aggression along the most heavily-congested roads; there are more prison riots when the population density in the prison is higher; a study shows there was more aggression in a day nursery as the nursery got more crowded.

However, this pattern is not found in families, as people expect others to be in close proximity. This suggests that it is not just a high density, but overcrowding that is the problem. There are also limitations to this, as some people do not find encroachment of their personal space to be a problem. Furthermore, there are also cultural differences eg Arabs tend to stand very close together. Also, if you can confront people about it, aggression can be reduced.

Both crowding and heat lead to physiological arousal which leads to aggression. However, this may depend on your interpretation of the arousal, for example, crowds can be uplifting, fun and exciting.

Noise

Noise is any unwanted sound that causes a negative effect. It can cause aggression when it is too loud or unpredictable. Glass and Singer conducted an experiment where participants were asked to complete a maths task and were then asked to complete a proof-reading task. During the maths task, some of participants were subjected to noise, but all of them had quiet during the proof-reading task. It was found that the people who had the noise in the first task made more mistakes in the second task. They made the most mistakes when the noise was very loud, was random (unpredictable) and when they had no control over it.