Introspection is contemplation on one's self, as opposed to extrospection, the observation of things external to one's self. Introspection may be used synonymously with self-reflection and used in a similar way. Introspection is like the activity described by Plato when he asked, "...why should we not calmly and patiently review our own thoughts, and thoroughly examine and see what these appearances in us really are?" (Theaetetus, 155) Cognitive psychology accepts the use of the scientific method, but rejects introspection as a valid method of investigation. 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. Introspection was once an acceptable means of gaining insight into psychological phenomena. 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 subject's 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.