Wundt, the father of modern psychology, is credited with opening the first psychology lab in Germany.
He used introspection in his work. This is a technique that is used to gain insight into how mental processes work. The Latin meaning, means to "look into".
It is the process by which a person gains knowledge about his or her own mental and emotional state. People were trained to report their inner experiences presented with a stimulus and all introspections were recorded strictly under controlled conditions. Each participant was given standardised instructions for replication purposes.