Final answer:
The phenomenon where runners in a park pick up their pace when another runner comes into view is known as 'social facilitation'. It is characterized by the improved performance of individuals on simple or well-rehearsed tasks due to the presence of others.
Step-by-step explanation:
Runners in a park were found to pick up their pace when another runner came into view; this finding illustrates the phenomenon of social facilitation. Social facilitation is the tendency for individuals to perform better on simple or well-rehearsed tasks in the presence of others. Contrary to the concept of social loafing, where individuals in a group might exert less effort because their individual performance is not being evaluated, social facilitation occurs because individuals are aware that their performance might be observed, which leads to increased arousal and motivation. This enhanced performance in the presence of others applies especially when the tasks involved are simple or if the individual has a high level of proficiency in the task. The presence of another runner acts as a social stimulus, subconsciously signaling the runners to heighten their performance.