Abstract: Apparatus is disclosed for use with one or more subjects simultaneously, for causing an output device to perform productive functions, such as various types of movement of an object, in response to the subject's movement between various brainwave states and combinations of brainwave states. When more than one subject is involved, the apparatus can generate an output signal indicating when all the subjects are producing a predetermined brainwave pattern simultaneously, when they are producing a predetermined brainwave pattern synchronously; when they producing a predetermined brainwave pattern coherently; or when, during a preceding predetermined interval of time, each of the subjects individually produced a predetermined brainwave pattern for more than a predetermined percentage of the interval of time.