The purpose of this work is to determine the parameters of spontaneous-thought-intrusions (daydreaming) and related mental activity such as insight, intuition, mindwandering, and curiosity. This is accomplished through the use of retrospective questionnaires and experimental manipulation. Topics of present interest are: (a) the lifespan changes in daydreaming in a longitudinal sample, and (b) the relation of daydreaming incidence to tasks of varying vigilance requirements.