In Asch's famous research study, participants agreed with people making an incorrect choice in a line length judgment task. This study is a classic study of

This study is a classic study of conformity.

Step 1: Understanding the question The question is asking about a famous research study conducted by Solomon Asch. In this study, participants were asked to judge the length of lines and often agreed with other people who were making an incorrect choice.

Step 2: Identifying the key concept The key concept in this question is the behavior of the participants who agreed with an incorrect choice. This behavior is related to a specific psychological concept.

Step 3: Linking the behavior to the concept The behavior of the participants in Asch's study - agreeing with an incorrect choice because others are doing so - is an example of conformity. Conformity is a type of social influence involving a change in belief or behavior in order to fit in with a group.

Step 4: Formulating the answer Therefore, Asch's study is a classic study of conformity.