Phenomenology is the study of subjective experience. It is an approach to psychological subject matter that has its roots in the philosophical work of Edmund Husserl. Early phenomenologists such as Husserl, Jean-Paul Sartre, and Maurice Merleau-Ponty conducted philosophical investigations of consciousness in the early 20th century. Their critiques of psychologism and positivism later influenced at least two main fields of contemporary psychology: the phenomenological psychological approach of the Duquesne School (The Descriptive Phenomenological Method in Psychology), including Amedeo Giorgi and Frederick Wertz; and the experimental approaches associated with Francisco Varela, Shaun Gallagher, Evan Thompson, and others (embodied mind thesis). Other names associated with the movement include Jonathan Smith (Interpretative Phenomenological Analysis), Steinar Kvale, and Wolfgang Köhler. Phenomenological psychologists have also figured prominently in the history of the humanistic psychology movement.