What was one of Carl Stumpf's major contributions to psychology?

Carl Stumpf made significant contributions to psychology, and one of his most notable achievements was the establishment of phenomenology as a key approach in understanding conscious experience. However, his work regarding the study of Clever Hans is particularly relevant. Clever Hans was a horse that appeared to demonstrate remarkable intelligence by answering questions posed to him through a form of non-verbal communication, specifically tapping his hoof. Stumpf's investigation into this phenomenon revealed the influence of the experimenter's cues on the horse's behavior, leading to important discussions on perception, expectation, and the implications of suggestibility in research settings. This work not only highlighted potential biases in psychological experimentation but also underscored the need for rigorous methodology and critical assessment of behavior, contributing to a better understanding of animal cognition and the psychology of learning. Stumpf's influence in examining these aspects of behavior and cognition represents a pivotal moment in the evolution of psychological science.