intersubjectivity, and wrote extensively on the topic. In German, his writings on intersubjectivity are gathered in volumes 13–15 of the Husserliana. In English, his best-known text on intersubjectivity is the Cartesian Meditations (it is this text that features solely in the Husserl reader entitled The Essential Husserl). Although Husserlian phenomenology is often charged with methodological solipsism, in the fifth Cartesian Meditation, Husserl attempts to grapple with the problem of intersubjectivity and puts forward his theory of transcendental, monadological intersubjectivity. Husserl's student Edith Stein extended intersubjectivity's basis in empathy in her 1917 doctoral dissertation, On the Problem of Empathy (Zum Problem der Einfühlung). Intersubjectivity also helps to constitute objectivity: in the experience of the world as available not only to oneself, but also to the other, there is a bridge between the personal and the shared, the self and the others. Psychology Discussions and theories of intersubjectivity are prominent and of importance in contemporary psychology, theory of mind, and consciousness studies. Three major contemporary theories of intersubjectivity are theory theory, simulation theory, and interaction theory. Shannon Spaulding, Assistant Professor of Philosophy at Oklahoma State University, wrote: Simulation theorists, on the other hand, claim that we explain and predict others' behaviour by using our own minds as a model and "putting ourselves in another's shoes"—that is, by imagining what our mental states would be and how we would behave if we were in the other's situation. More specifically, we simulate what the other's mental states could have been to cause the observed behaviour, then use the simulated mental states, pretend beliefs, and pretend desires as input, running them through our own decision-making mechanism. We then take the resulting conclusion and attribute it to the other person. Authors like Vittorio Gallese have proposed a theory of embodied simulation that refers to neuroscientific research on mirror neurons and phenomenological research. Spaulding noted that this debate has stalled in the past few years, with progress limited to articulating various hybrid simulation theories—"theory theory" accounts. To resolve this impasse, authors like Shaun Gallagher put forward interaction theory. Gallagher writes that an "... important shift is taking place in social cognition research, away from a focus on the individual mind and toward ... participatory aspects of social understanding...." Interaction theory is put forward to "galvanize" the interactive turn in explanations of intersubjectivity. Gallagher defines an interaction as two or more autonomous agents engaged in co-regulated coupling behavior.