Which psychologist conducted a classic study of conformity in which a group of confederates working with the experimenter were able to convince the actual participant that lines A and Y in the diagram above were not equal about 74 percent of the time?

Zimbardo is best known for the Stanford prison experiment, which investigated the psychological effects of perceived power and authority in a simulated prison environment. While his work is pivotal in psychology, it does not focus on conformity related to perceptual judgments, as Milgram's study does.

Festinger is famous for his theory of cognitive dissonance and his research on social comparison. Although his theories relate to conformity and social influence, they do not involve the specific experiment where confederates deceived participants about line lengths, as conducted by Milgram.

Bandura is recognized for his work on observational learning and the Bobo doll experiment, which examined aggression and imitation in children. His research does not pertain to the conformity study in question, which specifically involved the influence of a group on an individual's perception of similarity.