Final answer:
Oscar Pfungst believed that Hans, a horse who appeared to be able to perform complex arithmetic calculations, relied on visual cues from the audience's behavior to answer questions. This phenomenon is known as the Clever Hans effect. The correct answer is d) Clever Hans effect.
Step-by-step explanation:
Oscar Pfungst believed that Hans, a horse who appeared to be able to perform complex arithmetic calculations, was actually relying on visual cues from the audience's behavior to answer the questions. This phenomenon, where individuals unintentionally pick up on cues from their environment to produce the desired outcome, is known as the Clever Hans effect.
The Clever Hans effect is similar to the Hawthorne effect, which describes the increase in performance of individuals who are aware they are being observed by researchers or supervisors. Both effects highlight the importance of being aware of and controlling for the influence of external factors in research studies. The correct answer is d) Clever Hans effect.