The Würzburg School was an influential force in second generation German psychology
In 1896, one of Wundt's former Leipzig laboratory assistants, Oswald Külpe (1862–1915), founded a new laboratory in Würzburg. Külpe soon surrounded himself with a number of younger psychologists, most notably Narziß Ach (1871–1946), Karl Bühler (1879–1963), Ernst Dürr (1878–1913), Karl Marbe (1869–1953), and Henry Jackson Watt (1879–1925). Collectively, they developed a new approach to psychological experimentation that flew in the face of many of Wundt's restrictions. Wundt had drawn a distinction between the old philosophical style of self-observation (Selbstbeobachtung) in which one introspected for extended durations on higher thought processes and inner-perception (innere Wahrnehmung) in which one could be immediately aware of a momentary sensation, feeling, or image (Vorstellung). The former was declared to be impossible by Wundt, who argued that higher thought could not be studied experimentally through extended introspection, but only humanistically through Völkerpsychologie (folk psychology). Only the latter was a proper subject for experimentation.
The Würzburgers, by contrast, designed experiments in which the experimental subject was presented with a complex stimulus (e.g., a Nietzschean aphorism or a logical problem) and after processing it for a time (e.g., interpreting the aphorism or solving the problem), retrospectively reported to the experimenter all that had passed through his consciousness during the interval. In the process, the Würzburgers claimed to have discovered a number of new elements of consciousness (over and above Wundt's sensations, feelings, and images) including Bewußtseinslagen (conscious sets), Bewußtheiten (awarenesses), and Gedanken (thoughts). In the English-language literature, these are often collectively termed "imageless thoughts", and the debate between Wundt and the Würzburgers as the "imageless thought controversy."
Wundt referred to the Würzburgers' studies as "sham" experiments and criticized them vigorously. Wundt's most significant English student, Edward Bradford Titchener, then working at Cornell, intervened in the dispute, claiming to have conducted extended introspective studies in which he was able to resolve the Würzburgers imageless thoughts into sensations, feelings, and images. He thus, paradoxically, used a method of which Wundt did not approve in order to affirm Wundt's view of the situation (see Kusch, 1995; Kroker, 2003).
The imageless thought debate is often said to have been instrumental in undermining the legitimacy of all introspective methods in experimental psychology and, ultimately, in bringing about the behaviorist revolution in American psychology. It was not without its own delayed legacy, however. Herbert Simon (1981) cites the work of one Würzburg psychologist in particular, Otto Selz (1881–1943), for having inspired him to develop his famous problem-solving computer algorithms (e.g., Logic Theorist and General Problem Solver) and his "thinking out loud" method for protocol analysis. In addition, Karl Popper studied psychology under Bühler and Selz, and appears to have brought some of their influence, unattributed, to his philosophy of science (Ter Hark, 2004).