An apparatus for explicit and implicit attitude reaction monitoring on mobile computing devices and a method of operating such devices for interacting with a user and for guiding a behaviour of the user. The method comprising presenting the user with a series of tasks, each task requiring at least one response from the user and receiving the responses to the tasks from the user. The method further comprising, determining as a function of the received responses, one or more differences in the explicit and implicit attitudes of the user towards performing an intended behaviour, and delivering at least one message to the user, as a result of the differences in attitude, so as to guide the user to perform the intended behaviour.