Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's soul. Introspection is closely related to human self-reflection and self-discovery and is contrasted with external observation.
It generally provides a privileged access to one's own mental states, not mediated by other sources of knowledge, so that individual experience of the mind is unique. Introspection can determine any number of mental states including: sensory, bodily, cognitive, emotional and so forth.
Introspection has been a subject of philosophical discussion for thousands of years. The philosopher Plato asked, "…why should we not calmly and patiently review our own thoughts, and thoroughly examine and see what these appearances in us really are?" While introspection is applicable to many facets of philosophical thought it is perhaps best known for its role in epistemology; in this context introspection is often compared with perception, reason, memory, and testimony as a source of knowledge.
In psychology
Wundt
It has often been claimed that Wilhelm Wundt, the father of experimental psychology, was the first to adopt introspection to experimental psychology though the methodological idea had been presented long before, as by 18th century German philosopher-psychologists such as Alexander Gottlieb Baumgarten or Johann Nicolaus Tetens. Also, Wundt's views on introspection must be approached with great care. Wundt was influenced by notable physiologists, such as Gustav Fechner, who used a kind of controlled introspection as a means to study human sensory organs. Building upon the pre-existing use of introspection in physiology, Wundt believed the method of introspection was the ability to observe an experience, not just the logical reflection or speculations which some others interpreted his meaning to be. Wundt imposed exacting control over the use of introspection in his experimental laboratory at the University of Leipzig, making it possible for other scientists to replicate his experiments elsewhere, a development that proved essential to the development of psychology as a modern, peer-reviewed scientific discipline. Such exact purism was typical of Wundt and he instructed all introspection observations be performed under these same instructions: "1) the Observer must, if possible, be in a position to determine beforehand the entrance of the process to be observed. 2) the introspectionist must, as far as possible, grasp the phenomenon in a state of strained attention and follow its course. 3) Every observation must, in order to make certain, be capable of being repeated several times under the same conditions and 4) the conditions under which the phenomenon appears must be found out by the variation of the attendant circumstances and when this was done the various coherent experiments must be varied according to a plan partly by eliminating certain stimuli and partly by grading their strength and quality".
Titchener
Edward Titchener was an early pioneer in experimental psychology and student of Wilhelm Wundt. After earning his doctorate under the tutelage of Wundt at the University of Leipzig, he made his way to Cornell University, where he established his own laboratory and research. When Titchener arrived at Cornell in 1894, psychology was still a fledgling discipline, especially in the United States, and Titchener was a key figure in bringing Wundt's ideas to America. However, Titchener misrepresented some of Wundt's ideas to the American psychological establishment, especially in his account of introspection which, Titchener taught, only served a purpose in the qualitative analysis of consciousness into its various parts, while Wundt saw it as a means to quantitatively measure the whole of conscious experience. Titchener was exclusively interested in the individual components that comprise conscious experience, while Wundt, seeing little purpose in the analysis of individual components, focused on synthesis of these components. Ultimately, Titchener's ideas would form the basis of the short-lived psychological theory of structuralism.