Definition
The Clever Hans Effect refers to an unconscious nonverbal communication of information from a researcher or observer to a subject (animal or human), which creates the illusion of a cognitive, psychic, or supernatural ability in the subject.
Why It Matters
It warns researchers that subjects may be responding to hidden social cues rather than the problem being tested, which is essential for maintaining experimental integrity.
Core Concepts
- Hans the Horse: In 1904, a horse named Hans appeared to perform complex arithmetic and read German by tapping his hoof.
- Oskar Pfungst’s Discovery: A psychologist discovered that Hans was not “thinking” but reacting to the subtle, unconscious body language (tilts of the head, tension in the face) of his trainer or the audience as he neared the correct number of taps.
- Observer-Expectancy Effect: The more general phenomenon where a researcher’s expectations subtly influence the outcome of an experiment or the behavior of a subject.
- Double-Blinding: The primary solution to this effect, ensuring that neither the subject nor the person interacting with them knows the correct answer or the expected outcome.