Research into ‘contagion’ has been applied to a range of different behaviours. However, the failure to explain the apparent group-boundaries present in ‘passive’ social influence invites an explanation for behaviours incorporating social identification. Participants from the University of Sussex (n = 37) were presented with a video of two people itching. The participants’ level of social identification with the itching targets was manipulated so that they viewed the actors as belonging to either an ingroup or outgroup. Itching was both observed using a webcam and measured with a self-reported itchiness questionnaire. Where the itching targets were framed as ingroup, statistical significance was found for higher self-reported itchiness, and marginally significant results derived from observations to showed an increase in scratching behaviour, compared to when framed as outgroup. Other effects measured included the time of first scratch, the duration of itch per itch and self-relevance. Mediation and moderation analyses were also conducted to test for further possible explanations for the findings. This study contributes to the understanding of the process of ‘passive’ social influence, in which the level of social identification with the behavioural target impacts the spread of behaviour, rather than ‘mere exposure’, a concept that has been so widely adopted in the past. How and why do behaviours spread from person to person? In particular, how does aggression and violent behaviour spread? When, as in 2011, riots began in London, why did they then occur in Birmingham, Manchester, and Liverpool? One of the most common ways of addressing such issues is through the notion of 'contagion'. The core idea is that, particularly in crowds, mere exposure to the behaviour of others leads observers to behave in the same way. 'Contagion' is now used to explain everything from 'basic' responses such as smiling and yawning (where the mere act of witnessing someone yawn or smile can invoke the same response in another) to complex phenomena like the behaviour of financial markets and, of course, rioting. What is more, laboratory experiments on the 'contagion' of simple responses (such as yawning) serve to underpin the plausibility of 'contagion' accounts as applied to complex phenomena (such as rioting). Despite this widespread acceptance, the 'contagion' account has major problems in explaining the spread of behaviours. In particular, there are boundaries to such spread. If men smile at a sexist joke, will feminists also smile in response to the men's smiles? If people riot in one town, why is it that they also riot in some towns but not others? For example, in 2011, disturbances spread from London to Birmingham, Manchester and Liverpool but they did not spread to Sheffield, Leeds or Glasgow. 'Contagion' explanations cannot answer such questions because they assume that transmission is automatic. They do not take account of the social relations between the transmitter and receiver. We propose a new account of behavioural transmission based on the social identity approach in social psychology. This suggests that influence processes are limited by group boundaries and group content: we are more influenced by ingroup members than by outgroup members, and we are more influenced by that which is consonant with rather than contradictory to group norms. The social identity approach is therefore ideally suited to explaining the social limits to influence, both for 'basic' phenomena and rioting. In order to advance both theoretical understanding and practical interventions, our research will develop a social identity analysis of transmission processes at multiple levels. Accordingly, the aims and objectives of this research project are as follows: First, we will conduct a series of experimental studies on 'basic' behaviours (yawning, itching) to examine whether the effects of being exposed to a behaviour depend on observers and actors being fellow ingroup members. We will also examine 'complex' behaviours (aggression and rioting) to see if (1) observers are more influenced when the actors are ingroup members; (2) observers are more influenced by the responses of other observers when these are also ingroup members; (3) willingness to copy others depends upon whether their behaviour is consonant with observer group norms. Second, we will examine the spread of urban disorder during the 2011 English riots. We have been granted special access to the full data-set from the Guardian/LSE 'Reading the Riots' study (270 interviews with participants carried out immediately following the events). This, along with other secondary sources (such as detailed crime figures), will allow us to examine the extent to which the spread of these riots was linked to a sense of shared identity with those who had rioted previously (that is, those who rioted 'saw themselves' in those who rioted before them, and those who lacked such a sense were less likely to riot). Third, we will use our findings to generate a wider debate about the nature of psychological transmission and the practicalities of addressing them. Activities will include workshops which will bring together researchers, practitioners (e.g., the police) and policy-makers in local and national government to address how we can mitigate against the spread of riots and violence.

Forty-two undergraduate students from the University of Sussex took part in this study; (25 Female, 17 male) aged between 19 and 23 (M= 20.79, SD= 1.07). Participants were either approached around campus or scheduled to meet via email and randomly assigned to one of three groups: ingroup, outgroup, or control group. Participants were given a laptop with a webcam and instructed to complete part 1 of a questionnaire (ingroup and outgroup conditions only), then watch a short video and finally complete part 2 of the questionaire (all conditions).