Final answer:
Soloman Asch conducted experiments on conformity by showing participants varying line lengths and asking them to match them, revealing the impact of group pressure on individual decisions.
Step-by-step explanation:
The sociologist pioneer who performed an experiment in which he showed a group of participants a paper with three lines on it, all varying in length, and asked them to compare the lines was Soloman Asch. Solomon Asch conducted several experiments in the 1950s to determine the impact of group pressure on individual judgment and conformity. Participants were shown a series of line segments and were asked to identify which line segment from the first group most closely resembled the fourth line segment in length. Despite the apparent simplicity of the task, Asch's experiments revealed that people often conformed to the group's incorrect choice, highlighting the strong influence of social pressure on individual behavior.