Introspection is the self-observation and reporting of conscious inner thoughts, desires and sensations. It is a conscious mental and usually purposive process relying on thinking, reasoning, and examining one's own thoughts, feelings, and, in more spiritual cases, one's soul. It can also be called contemplation of one's self, and is contrasted with extrospection, the observation of things external to one's self. Introspection may be used synonymously with self-reflection and used in a similar way.
Behaviorists claimed that introspection was unreliable and that the subject matter of scientific psychology should be strictly operationalized in an objective and measurable way. This then led psychology to focus on measurable behavior rather than consciousness or sensation. Cognitive psychology accepts the use of the scientific method, but rejects introspection as a valid method of investigation for this reason. It should be noted that Herbert Simon and Allen Newell identified the 'thinking-aloud' protocol, in which investigators view a subject engaged in introspection, and who speaks his thoughts aloud, thus allowing study of his introspection.
On the other hand, introspection can be considered a valid tool for the development of scientific hypotheses and theoretical models, in particular in cognitive sciences and engineering. In practice, functional (goal-oriented) computational modeling and computer simulation design of meta-reasoning and metacognition are closely connected with the introspective experiences of researchers and engineers.
Introspection was used by German physiologist Wilhelm Wundt in the experimental psychology laboratory he had founded in Leipzig in 1879. Wundt believed that by using introspection in his experiments he would gather information into how the subjects' minds were working, thus he wanted to examine the mind into its basic elements. Wundt did not invent this way of looking into an individual's mind through their experiences; rather, it can date to Socrates. Wundt's distinctive contribution was to take this method into the experimental arena and thus into the newly formed field of psychology.