SLT and Aggression

What is Deindividuation?

Deindividuation refers to a psychological state in which individuals within a group lose their sense of personal identity and feel less accountable for their own behaviour. The term was coined by Festinger et al. (1952), who observed that submersion in a group reduced self-awareness and loosened normal social constraints.

Zimbardo's Model (1969)

Zimbardo developed the most influential account: group membership and anonymity produce a state of deindividuation characterised by reduced private self-awareness, weakened inhibitions, and impulsivity. This makes antisocial behaviour more likely because the individual no longer feels personally responsible. The Stanford Prison Experiment (Haney, Banks & Zimbardo, 1973) is often cited as a real-world illustration — guards adopted brutal roles partly due to uniform and group identity.

Research Evidence

Mann (1981) — Crowd Baiting

Mann analysed 21 newspaper accounts of people threatening to jump from tall buildings. In 10 of the 21 cases, crowds below baited the individual. Crucially, baiting was significantly more likely when crowds were large and when events took place at night — both deindividuating conditions. This naturalistic evidence supports Zimbardo's model, though it cannot establish causation.

Mullen (1986) — Lynching Meta-Analysis

Mullen content-analysed newspaper reports of 60 lynchings in the United States. Larger mob size was associated with greater atrocity in the killing. As the number of lynchers per victim increased, the acts became more savage — consistent with the prediction that crowd size amplifies deindividuation.

Challenges: The SIDE Model

Reicher, Spears & Postmes (1995) proposed the Social Identity model of Deindividuation Effects (SIDE). They argued that anonymity does not simply reduce self-awareness; instead, it shifts attention away from personal identity towards group identity. Behaviour then conforms to group norms, which can be prosocial or antisocial depending on context. This better explains why carnival crowds or online communities can display strongly norm-governed behaviour even under anonymity.

Johnson & Downing (1979) directly tested this: participants wore either a KKK-style costume or a nurse's uniform before administering electric shocks. Those in KKK costumes gave more shocks; those in nurse uniforms gave fewer. The direction of deindividuated behaviour depended on the costume's social cues — directly contradicting the assumption that deindividuation always leads to aggression.