Deindividuation is a social psychological explanation of aggression it is the process whereby people lose their sense of socialised individual identity making them more likely to engage in behaviour that is deemed antisocial. Zimbardo suggested that deindividuation is due to anonymity, reduced responsibility, increased arousal, sensory overload and altered consciousness due to drugs and alcohol.
Individuals become deindividuated when anonymous because there is less awareness of their individuality, which makes them seem almost faceless when they are merged with a large group of people or when wearing a mask. They can also be deindividuated in times of increased arousal and sensory overload this can happen when in crowds where it is loud and packed especially if people are getting intoxicated by drugs and alcohol. Likewise in large groups an individual may act violent due to the responsibility not being completely on them. By being masked, in uniforms, groups, in the dark etc. can influence deindividuation

Prentice – Dunn and Rodger suggest that an individual loses different types of self-awareness in a group. Not concerning about the impression you have to the people around you leads to less public self-awareness and losing concerns you have for own standards and morals leads to less private self-awareness. The loss of private self-awareness that leads to increased anti-social behaviour.
Furthermore, Festinger et al suggested that when an individual is submerged in a group there I a reduction of inner restraints and self-awareness causing them to forget consequence and social norms which may lead to anti-social behaviour.
The experiment for prentice and Festinger were carried out 30 years later and the results were the same suggesting that a loss in public or private self-awareness can cause an individual to become deindividuated.

A study that support deindividuation as an explanation of aggression was conducted by Zimbardo et al in 1973 who aimed to test the effect of deindividuation on prison guards and prisoner aggression. He created a stimulated prison of 24 male participants. Half were assigned to be guards and the others were prisoners. The guards wore reflective glasses, uniform and carried hand cuffs. While the prisoners wore lose smocks and were only referred to by number. The guards created a brutal atmosphere becoming aggressive verbally and physically. Both participants showed signs of deindividuation and the experiment that was meant to last 2 weeks go called off after just 6 days.
This shows that due to the guards wearing the uniform and sunglasses they were not acting themselves and therefore did not feel responsible their actions when acting out the role of the guard.

This study can be critiqued methodologically. All the participants Zimbardo used were males in their 20’s hence the sample is gender biased as all the men were white males. This means that the results cannot be applied to a wider population as aggression may vary in women or in other ethnicities’. However, the experiment was in a real life environment. Even though the situation was tightly controlled, the study still had ecological validity for example in the way that he had the prisoners arrested from their homes. This means that the findings can be generalised to real life situations hence aggression is caused by anonymity.
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Another study supporting deindividuation as an explanation of aggression was conducted by Diener et al who conducted a naturalistic study to assess the effects of 3 deindividuation variables on stealing by children. He found that children were much more likely to steal when dressed up in Halloween costumes or when in the presence of a group. The high rate of stealing occurred among anonymous children in group. This supports the deindividuation theory as the costumes hide the identity of the children therefore making them anonymous this suggests that deindividuation does cause aggression.

The study has a large sample as there were 1300 children in the study this means that the findings of the study is generalisable hence the children are more likely to be aggressive in groups or when anonymous.

A study that challenges deindividuation as an explanation of aggression was conducted by Gergen and Barton in the darkened room aroused study six men and six women, who did not know each other, were put into groups. They were put in either normally lit rooms (control group) or in a completely dark room (experimental group) and were told that there was nothing special that the experimenters wanted them to do. The results showed that the participants in the dark room began to get physical, half of them hugged each other, some of them became quite intimate and 80% reported feeling sexually aroused. This challenges deindividuation as the participants did not become aggressive or anti-social when they could not be identified.
This study has a low sample size as only 12 people participated in the study. This means that the findings cannot be generalised therefore if more people were to have been in the study there may have been participants who were aggressive in the experimental setting.

A debate concerning the deindividuation is that it takes a determinist view of aggression; explanations are deterministic if they suppose that given a certain criteria, a given behaviour is guaranteed. The theory states that aggressive behaviour is a result of losing one’s conscious constraints in the presences of a group and it denies that the individual is responsible their behaviour. It also takes a reductionist approach as it fails to consider other factors which may influence aggression such as biological causes such as neurotransmitters. Therefore, the deindividuation theory should be viewed with caution as an explanation of aggression.

Furthermore, research into the deindividuation raises ethical issues. The research done by Zimbardo shows a violation of the ethical guideline relating to protection from harm, the research has been criticised for its numerous violations of the BPS’s ethical guidelines. The experiment was designed to last for two weeks, but was stopped after 6 days due to the level of aggression shown by the guards and the inhumane treatment of the prisoners causing long term psychological damage on the participants. This causes the research to be unethical and when considering research into aggression, it needs to be viewed with caution.

Finally, an issue with the deindividuation is that it has real life applications this means that the findings and explanations of deindividuation can be applied directly to real life scenarios. It explains how and why guards in Abu Ghraib are able to torture the prisoners to such an extreme extent. It may be due to their uniform which gives them a sense of anonymity and they can torture prisoners as the responsibility is not completely on them. Therefore, deindividuation is a strong as an explanation of aggression.