Why does the psychology of science need to be classified as its own discipline?
Because psychology can shed light on the personalities, developmental histories, cognitive processes of scientific interest, talent, and creativity that other disciplines do not. History of science touches these topics sometimes, but in case studies in a historical context. Psychology is the only discipline that studies these topics empirically.
How is the psychology of science different from the philosophy of science and the sociology of science?
Psychology is the only study of science that combines an empirical perspective with a focus on the individual. It also is the only study of science that uses the experimental methods. Also psychology uniquely focuses on psychological factors such as personality, motivation, brain activity, and development of thought. Philosophy is mostly analytical, that is non-empirical and does not test its own hypotheses the way psychology of science does. Sociology ignores or even refutes the individual in a social context and focuses on sociological structures and forces. The individual doesn't really matter.
Does the psychology of science address the psychology of rationality? That is, rationality as defined by cognitive science (instrumental and epistemic rationality).
Psychology, or more specifically cognitive psychology, very much is concerned with rational and non-rational cognitive processes, often by comparing experts to novices and seeing what distinguishes the two groups in how they identify and solve scientific problems. Cognitive scientists like Paul Thagard, Herb Simon, and Kevin Dunbar have examined rationality; but to the extent that psychology weighs in against pseudoscience, anti-science, and social constructivism, it takes a stance on rationality and the scientific method being of value. A very good cognitive science perspective on science the edited volume by Carruthers, Stich, and Siegal (2002) entitled the cognitive basis of science.
What books do you recommend to a lay audience if they are interested in learning more about the psychology of science?
There no trade books for a wide general audience, so my 2006 book (the psychology of science and the origins of the scientific mind) would be one possible lay audience book (no stats in it).
What books do you recommend to the scientist that is interested in learning more about the psychology of science?
There are many books on the topic that might be of interests to scientists;
--the handbook of the psychology of science, edited by Feist and Gorman (2013) (springer publishing)
--creativity in science, by Simonton (2004)
What is your favorite book?
I assume you mean in the psychology of science. The books that for me have a special place were the two that inspired me to become a psychologist of science during graduate school, namely the edited volume by Gholson, Shadish, Neimeyer and Houts (1989) psychology of science: contributions to metascience and Dean Simonton's (1988) scientific genius: a psychology of science.
Where do you see the discipline- the psychology of science- in five years?
I would love to say that it would have PhD programs and research centers, but I think that is overly optimistic. More realistically, I think our society--the international society for the psychology of science and technology--will continue to have it's biennial conferences and have a small but loyal core group of scholars working and identifying themselves as psychologists of science.