1. Despite the fact that his teacher Wundt believed that thinking was beyond the reach of experimental psychology, Külpe first turned to the experimental study of higher psychic processes: thought and volition by the using the systematic introspection.
2. Method. He used the systematic experimental introspection or controlled self-observation(invented by Karl Marbe).
Method was not in the simultaneous unfolding of processes of thinking and its observation but in retrospective observation of the own cognitive processes during the task.
3. In this case the main object of study by this method was a procedural aspects of thinking, rather than its result.
4. The most important result of his research was the discovery of an independent mental reality, which cannot be reduced to the sensory content.
5. He introduced the concept of the "imageless thought" seemed to be that thoughts can occur without a particular sensory or imaginable content.
6. Kulpe and his colleagues found that the essence and specific of thinking is the presence of special “meanings” that impart unity, stability, activity, imagelessness and direction.
7. Philosophy. He was a Representative of critical realism. The main theme of Külpe’s work was the psychological foundations of epistemology and the theory of knowledge.
8. Founded the Institute of Psychology in the "Alte Universität" in Wurzburg together with Karl Marbe (1896).
Külpe studied as a doctoral student and assistant to Wundt at the University of Leipzig. In 1887, Külpe was awarded his PhD. (Thesis “The Theory of Sensual Feeling".) As a student of Wilhelm Wundt, worked 8 years at the Leipzig laboratory (1887-1894). In 1896 Külpe had founded a laboratory at the University of Würzburg and remained there for fifteen years. He was Professor at Würzburg (1894–1909) and Bonn (1909–13). In 1913 Külpe took a post at the University of Munich (1913-1915).
His best known pupils were N. Ach and K. Bühler, O.Zelz, J. Angell. In addition Max Wertheimer, Kurt Koffka, Charles Spearman worked with him for a time.
Wilhelm Wundt and Edward Titchener were profoundly opposed to the idea of imageless thought, in spite of this Külpe and Wundt remained on friendly terms personally.
He lived a large portion of his life with his older, unmarried cousins, Ottillie and Marie Külpe, at their residences in Leipzig, Würzburg, Bonn, and Munich. He never married either and throughout the years he devoted an immense amount of his time to his work.