Deindividuation describes the phenomenon when an individual loses certain aspects of self-awareness within a group environment. Mostly commonly applied to situations of group violence or negative behaviors, deindividuation can arguably cause a group member to lose sense of his or her personal obligations, morals, and sense of responsibility. In this example, the young man describes getting "caught up" and "carried away" with the group while failing to consider his personal role in the events. Such a description would be considered characteristic of deindividuation.

The bystander effect refers to the inverse relationship between the number of people witnessing a negative event and the number of people that will assist in alleviating the negative outcome. As the young man described was a participant in the riot, rather than a bystander, we can eliminate this answer choice.

Social facilitation describes the likelihood for individuals to perform well on simple tasks when being watched by a group. Essentially, when one's talents are being evaluated by others, one tends to perform their existing talents better. This phenomenon is relatively unlinked to the situation described in the question.

Groupthink is a decision-making phenomenon driven by the desire for harmony within a group, and is used to justify irrational decisions and choices. A certain outcome may be reached solely to stabilize group loyalty and cohesion, rather than based on the consequences and effects of the outcome. While the situation described in the question outlines an instance of a group acting cohesively, the young man's response stems from a lack of cognitive awareness rather than a conscious desire to adhere to the group's actions.

Group polarization is another decision-making trend, and describes the tendency for group decisions to be more polarized toward given extremes than the viewpoints of the individual members. While the situation described certainly outlines a shift from moderate to extreme, there is again the issue of cognitive awareness and intention that allow us to eliminate this answer choice.

Deindividuation occurs when people are in a situation with a high degree of arousal and low feelings of responsibilities. In other words, it is a situation where individuals experience a loss of restraint and individual identity that is replaced with mob mentality. It can be described as a lack of self-awareness and results from disconnection of behavior from attitudes. Several factors create ideal conditions for deindividuation: group size, physical anonymity, and arousing activities.

Aggregates are groups of people who frequently exist in the same space but have little interactions. A person would be likely to experience deindividuation in this setting because of concepts like the bystander effect- people assume less responsibility because they believe someone else will take care of whatever issue is at hand, that someone else will do the right thing.

On the other hand, the other choices are incorrect. “Primary groups” are those close to you that you bond and interact heavily with; they serve expressive functions (i.e. where emotional needs are being met). We are closer and feel more generally responsible with these people. “Secondary groups” are usually task-oriented, impersonal, temporary, business-like relationships with instrumental purposes. We would be less likely to experience deindividuation with these groups because we would have a high feeling of responsibility for the tasks the group has been formed to tackle. “Counter-cultures” are distinct subcultures focused on stopping some dominant aspect of mainstream culture (like "anti-vaxxers"). Like an “out-group,” they are not a group with which someone would generally find common values, so they would be unlikely to induce deindividuation.

According to the bystander effect, there is diffusion of responsibility; thus, most people assume, often mistakenly, that “someone else” will take the necessary actions such as calling the police or ambulance. The likelihood of someone taking appropriate action is inversely correlated with the number of people at the scene. 

While intriguing, the other choices are incorrect. A self-serving bias is the tendency to attribute successes to ourselves and failures to external causes. Conformity is where one adjusts one’s thinking or behavior because of that of others. Deviance is described as a violation of society’s standards of conduct or expectations. Groupthink is a psychological phenomenon that occurs within a group of people, in which the desire for harmony or conformity in the group results in an irrational or dysfunctional decision-making outcome.

Also called bystander apathy, the “bystander effect” describes cases where individuals do nothing to help someone in need when other people are around. Many think that if no one else is reacting, then it must mean that the problem is not worth solving. A landmark case occurred in New York when Kitty Genovese was stabbed to death in a public area. Although 38 people witnessed the murder, no one stepped in to help. This scenario is a classic example of the bystander effect. Although the people could be described as conforming to one another, bystander effect is a more specific description.

The correct answer is "groupthink," the concept that individuals stifle their ideas in the group to achieve concensus. Group polarization is not the correct answer, because it means that groups might select options that are more extreme than individual members of that group might select, and this is not illustrated in the example above. The other concepts are concepts of psychology, but are not related to group processes. 

Group polarization describes the phenomenon when individuals make more extreme decisions when acting together as a group than they would by themselves. In this scenario, as individuals—the jurors—believed in their respective points of view from the beginning; however, after they formed oppositional groups, they became even more entrenched in their points of view.

The other choices are incorrect due to various reasons. Cognitive appraisal is a process where a physiological arousal is assessed in the brain and processed for the appropriate physiological and psychological coping strategies. It has nothing to do with the juror situation. Informational influence is a group effect arising from a group’s desire to be correct and to understand how to act best in a given situation. While this may play a role here—because the jury may be trying to be correct and act in the interest of justice—it has split into two opposing camps and one group will not “act correctly." Social categorization is the process by which people sort themselves into categories. This may be happening in this situation when the jury broke into two camps—those who believe the defendant is guilty and those who believe the defendant is not guilty—but it is not the primary effect. The self-serving bias describes the attribution of positive experiences to our own character and actions but negative experiences to factors external to our own character and actions. While this may affect the jurors’ interpretations of their own opinions and actions, it does not explain why they are more entrenched in their beliefs after discussing the matter with others who believe the same thing they do.