Immanuel Kant distinguished transcendental apperception from empirical apperception. Philosopher Gottfried Wilhelm Leibniz introduced the concept of apperception to this philosophical approach to attention. McClelland used the thematic apperception test in order to test this part of his theory. Wundt believed that creative synthesis was entwined with all acts of apperception. Failure of apperception is seen in delirious states. He also collaborated on the Thematic Apperception Test. It was there she developed a system to analyze the Thematic Apperception Test. Examples of such tests include the Rorschach test and the Thematic Apperception Test. Murray notes that both Pressive Perception and Apperception are largely unconscious. The term was later adapted in psychology by Johann Friedrich Herbart (see Apperception). The Thematic Apperception Test (TAT) is commonly used for assessing motives. Apperception theory applied equally for general psychology and cultural psychology. Apperception is Wundt's central theoretical concept. Apperception played a key role in Herbart's educational theory. Apperception is required for a perceived event to become a conscious event.