 Psychologist John B. Watson calls Juan Luis Vives the father of modern psychology because, in his book "De Anima et Vita" ("The Soul and Life"), he was the first to recognize the importance of empirical investigation.In his work on memory, Vives found that the more closely one attends to stimuli, the better they will be retained.By the 1990's, psychologists began using positron emission tomography (PET) and later functional magnetic resonance imaging (fMRI) to image the brain while monitoring tasks involving attention.