Abstract
The progress of scientific psychology during the late 19th century brought a new topic into the long-discussed issue of self-observation, namely that of psychological experiment. Towards the end of the century, though, Avenarius proposed a new model of psychology, in which psychophysical experiment was no longer a mere aid for self-observation, rather becoming a new paradigm for psychology. In his Grundriss Külpe embraced this new idea of psychology as a science based on the observation of the dependency between the brain and the psychic contents, and consequently as a collective research. Although later Külpe and his followers rejected the psychophysical approach, they kept the idea that psychological observation was not self-observation, since psychology could become an objective and general science only through experiments in which the researcher registered the experiences of a third person.