This theory is based on Le Bon's 'Crowd Theory'. He described how an individual transformed when part of a crowd, claiming that anonymity, suggestibility and contagion mean that collective mind takes over the individual. The individual then loses self-control, and goes against social norms.
Deindividuation is a psychological state characterised by lowered self evaluation and lowered concern about evaluation by others.
The psychological state of deindividuation is aroused by being part of a crowd or large group.
Contributing factors are anonymity (Wearing a uniform) and altered consciousness due to drugs or alcohol (Zimbardo, 1969)
Zimbardo suggested that being part of a crowd can diminish awareness or our own individuality. In a large crowd, each person feels faceless and anonymous - the larger the group, the greater the anonymity. There's a diminished fear of negetive evaluation by others and a reduced sense of guilt.
Deindividuation - Research
Anonymity - Zimbardo (1969) carried out a series of experiments that were to develop the deindividuation theory. Groups of four female undergraduates were to deliver electric shocks to 'aid the learning' of another student'. Half of the participants were dressed in bulky clothing with hoods that hid their faces, and the other half wore their own clothes and were given name tags. Both sets of participants were told they could see the shock-ee. Participants in the deindividuation condition shocked the person for twice as long as the other group.
The Faceless Crowd - Mullen (1986) analysed newspaper cuttings of 60 lynchings in the US between 1899 and 1946. He found that the more people there were in the mob, the greater the savagery with which they killed their victims.
The Baiting Crowd - Mann (1981) analysed 21 suicide jumps in the US. He found that 10 in 21 of the jumps, a crowd had gathered that had 'baited' the jumper. These incidents tended to occur at night time and when there was a larger crowd, aiding the anoymity and facelessness.
Deindividuation - Evaluation
Gender bias (IDA) - Cannavale (1970) found that male and female groups responded differently under deindividuation conditions reflecting a gender bias in the theory. An increase in aggression was found only in the all male groups.
Real-world application (IDA) - Mann's baiting crowd
Cultural differences - Watson's warriors experiment. Watson looked at tribesmen who went to war with other tribes. He found that those warriors who wore face paints were more destructive towards their victims, compared to those who did not change their appearance.
Lack of research support - A meta-analysis of 60 studies concludes that there is not enough evidence to support the major claims of the deindividuation theory. Spivey and Prentice-Dunn found that deinviduation can lead to pro-social behaviours as well as anti-social.
Neural Factors in Aggression
Neurotransmittors - There are chemicals which enable impulses to be transmitted from one area of the brain to another
Serotonin - Thought to reduce aggression by inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response. Low levels of serotonin have been associated with aggressive behaviour. Some drugs are thought to lower serotonin levels. Mann gave 35 healthy participants dexfenfluramine, which is known to deplete serotonin levels. He found that in the drugs causes aggression and hostility in the male participants only.
Dopamine - The link with aggression and dopamine is not as strong as it is with serotonin but some evidence suggests that there is a link. Increases in dopamine activity via the use of amphetamines have also been associated with increases in aggressive behaviour.
Antipsychotics which have been know to reduce dopamine activity in the brain have been showed to reduce aggression levels.
Neural Factors - Evaluation
Evidence from non-human studies - Raleigh et al have added support for the importance of serotonin in aggressive behaviour by using vervet monkeys. Individuals fed on a diet containing tryptophan (increases serotonin levels) exhibited decreased levels of aggression. Individuals fed on a diet low in tryptophan exhibited increased levels of aggression. This suggests that the difference in behaviour could be attributed to the serotonin levels.
Evidence from anti-depressants - If low levels of serotonin are associated with low impulse control, drugs that clinically raise serotonin levels should produce a concurrent lowering aggression. This was proved by Bond (2005).
Dopamine - Couppis and Kennedy (2008) found that in mice, a reward pathway in the brain becomes engaged in response to an aggressive event, and that dopamine acts as a positive reinforcer in this pathway. This suggests that individuals will actively seek out aggressive encounters because they produce a rewarding sensation.
Hormonal factors in aggression
Testosterone - Dabbs et al (1987) measured salivary testosterone in violent and non-violent criminals. Those with the highest testosterone levels had a history of primarily violent crime, whereas those with lower levels of testosterone had commited non-violent crime.
Lindman et al (1987) found that young males who behaved aggressively when drunk had higher testosterone levels than those who did not act aggressively when drunk.
The challenge hypothesis - Wingfield et al (1990) proposes that in monogamous species, testosterone levels should only rise above the baseline level in response to social challenges, such as male-male aggression or threats to status. As the human species is monogamous, this would predict that male testosterone levels rise sharpy in response to such challenges.