This study aimed to investigate the relationship between shared social identity and the transmission of behaviour via observation alone. The study used a 1x3 design (In-group/Out-group/undefined) in which participants watched a video of actors scratching various body parts and their scratching responses were measured using a video recorder and a self report questionnaire. There were no significant main effects of condition on shared identity, self-reported itchiness, time to first scratch, number of scratches, duration of scratches of average scratch duration. However, there were significant differences between IG and OG (planned contrasts) for shared identity and self-relevance but no significant differences between IG and OG (planned contrasts) for self-reported itchiness and the behavioural data. Using only IG/OG participants, there was a significant indirect effect for Condition (IG/OG) - Shared Identity - Self-reported Itchiness - Number of Scratches (serial mediation using PROCESS v3). There were no significant moderation effects of Identity strength between Condition (IG/OG) and Shared identity or any of the scratching variables. This study is part of a series of studies that 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. 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.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.

Participants from the University of St Andrews (n = 64) took part in this study. They were recruited through SONA, the School of Psychology & Neuroscience's online research participation system and met with a researcher in the School's immersion lab. First, the participants’ level of social identification with the scratching targets was manipulated in the introduction to the questionnaire such that they viewed the actors as belonging to an in-group, out-group or to no particular social group. They were then presented with a questionnaire that made their identification with the actors more salient. Next they watched a short video of a male and female scratching various body parts and labelled as either a student (in-group condition), a Dundee student (out-group condition) or not identified as belonging to any particular group. Scratching was both observed using a video recorder and measured with a self-reported itchiness questionnaire after the video ended.