Brainwave entrainment is any practice that aims to cause brainwave frequencies to fall into step with a periodic stimulus having a frequency corresponding to the intended brain-state (for example, to induce sleep), usually attempted with the use of specialized software. It purportedly depends upon a “frequency following” response on the assumption that the human brain has a tendency to change its dominant EEG frequency towards the frequency of a dominant external stimulus.[citation needed] Such a stimulus may be aural, as in the case of binaural or monaural beats and isochronic tones, photic (visual), as with a dreamachine, a combination of the two with a mind machine, or electromagnetic radiation.-wikipedia