instead introspect upon what you know has occurred. As a result of his experiment, Külpe determined that visual perception is determined not only by external stimulation but also by Aufgabe, which is another word for the task or directive. Since he varied the Aufgabe (task) slightly in each session of the experiment, he was able to find a correlation between the range of attention and degree of consciousness. He found that the wider one’s span of attention, the lower one’s degree of consciousness is to any specific aspect, and vice versa. He concluded that there is a limited amount of energy driving attention and that this limitation is constant. He also concluded that the abstraction process is based on apprehension, rather than sensational differences in presentation, and that these two concepts are distinct. Mental set Külpe and his Würzburg associates also used his abstraction experiments to reject associationism as the elementary thinking method. For example, in situations where participants were asked to provide a superordinate category, or superior group within a classification system, for birds, they were more likely to respond by saying, ‘Animal’ than a specific bird such as a ‘hummingbird.’ As a result, Külpe and the students at the Würzburg laboratory concluded that behavior such as the above example could not be explained according to associationistic logic. They determined that the actual task, instead of the stimulus directs the thinking process. This mechanism became known as the mental set. Specifically the mental set refers to an innate tendency to respond a certain way. Eventually the mental set was seen as a factor that could account for a large portion of the variation in the ways that people solve problems. Major works Oswald Külpe’s books and published works cover a variety of subject matter, which impacted his interest in psychology. Examples of his publication topics include logic, aesthetics, philosophy, and epistemology. His first major book, published in 1893, was Grundriss der Psychologie. The handbook summarized a comprehensive amount of experimental research at the time, including new research on reaction time, contributions to psychophysics, Carl Stumpf’s research into tonal fusions, and Hermann Ebbinghaus’ research on memory. He defined psychology as, “the facts of experience," as the book concerned itself strictly with scientific fact. The lack of focus on the concept of thought in his book is interesting because the Würzburg school greatly researched mental set and imageless thought. He once