A person's performance on tasks can be enhanced or impaired by the mere presence of others, and a person's behavior as part of a group can be quite different from the person's behavior when acting alone. In certain cases, individual performance can be either helped or hindered by the physical presence of others. The term social facilitation refers to any effect on performance, whether positive or negative, that can be attributed to the presence of others. Research on this phenomenon has focused on two types of effects: audience effects (the impact of passive spectators on performance) and coaction effects (the effect on performance caused by the presence of other people engaged in the same task).

In one of the first studies in social psychology, psychologist Norman Triplett looked at coaction effects. He had observed in official bicycle records that bicycle racers pedaled faster when they were pedaling against other racers than when they were racing against the clock. Was this pattern of performance peculiar to competitive bicycling Or was it part of a more general phenomenon whereby people work faster and harder in the presence of others than when performing alone Triplett set up a study in which he told 40 children to wind fishing reels as quickly as possible under two conditions: alone or in the presence of other children performing the same task. He found that the children worked faster when other reel turners were present than when they performed alone.

Later studies on social facilitation found just the opposite effect that the presence of others, whether co-acting or just watching, could hurt or diminish individual performance. Social psychologist Robert Zajonc proposed an explanation for these seemingly contradictory effects. He reasoned that we become aroused by the presence of others and that arousal facilitates the dominant response, the one most natural to us. On simple tasks and on tasks at which we are skilled, the dominant response is to perform effectively. However, on tasks that are difficult or tasks we are just learning, the incorrect response (making a mistake or not performing effectively) is dominant. This reasoning accounts for the repeated findings that, in the presence of others, performance improves on tasks that people do easily but suffers on difficult tasks. Other researchers have suggested that concern over the observers' evaluation is what most affects people's performance, particularly if they expect a negative evaluation.

What happens in cooperative tasks when two or more people are working together instead of competing Do they increase their effort or slack off Researcher Bibb Latan¨|used the term social loafing to refer to people's tendency to exert less effort when working with others on a common task than when they work alone. Social loafing occurs in situations where no one person's contribution to the group can be identified and individuals are neither praised for a good performance nor blamed for a poor one. In one experiment, Latan¨| and others asked male students to shout and clap as loudly as possible, first alone and then in groups. In groups of two, individuals made only 71 percent of the noise they had made alone; in groups of four, each student put forth 51 percent of his solo effort; and with six students, each made only a 40 percent effort.

Harkins and Jackson found that social loafing disappeared when participants in a group believed that each person's performance could be monitored and evaluated; indeed, even the idea that the group performance may be evaluated against some standard can be sufficient to eliminate the loafing effect. When a group is relatively small and group evaluation is important, some members will even expend extra effort if they know that some of their coworkers are unwilling, unreliable, or incompetent to perform well. Moreover, social loafing is unlikely when participants can evaluate their own individual contribution or when they have a personal stake in the outcome.It is also unlikely when participants feel that the task is challenging or when they are working with close friends or teammates. Some 80 experimental studies have been conducted on social loafing in diverse cultures. Based on evidence these studies have produced, social loafing probably occurs in almost all cultures.