A mind machine (aka brain machine or light and sound machine) uses pulsing rhythmic sound, flashing light, or a combination of these to alter the frequency of the user's brainwaves. Mind machines can induce deep states of relaxation, concentration, and in some cases altered states of consciousness, which have been compared to those obtained from meditation and shamanic exploration. Photic mind machines work with flickering lights embedded in sunglasses or a lamp that sits above or facing the user's head. The user then "watches" with their eyes closed. The process applied by some of these machines is said to induce brainwave synchronisation or entrainment. History The influence of rhythmic sounds and drums to enter altered states of consciousness is used in different indigenous tribes (see Shamanic music), as well as optical stimulation produced by the flickering light of camp fires or pressing lightly on the eyeballs. This "stroboscopic photo-stimulation produces 'photic driving', the alpha type of brain electrical activity associated with an altered state in which people are susceptible to suggestion". ( p. 12). The first scientific observations were made by William Charles Wells in the 1790s who described different effects of binocular vision. His results were later transferred to be applied in binaural beats. Visual experiments with flickering lights were conducted in the 1940s by William Grey Walter who used stroboscopic light flashes to measure their effects on brain activity, assessed with EEG. He reported effect not just on visual areas but on the whole cortex. During the '60s and '70s the interest in different methods to induce altered states without the use of drugs were rising. Some of the induced states by rhythmic light and sound combinations were even described as psychedelic-like, while these claims lack adequate measurements for their similarity. In this line, numerous nightclubs began using strobes to maximize the effects of the music for dancing. The development of alpha EEG feedback (see neurofeedback) is an important starting point for biofeedback and its explicit use for entering altered states of consciousness. In these decades, Jack Schwarz built one of the first mind machines using rhythmic sounds and variable frequency lights in goggles to produce certain mental states. Enterprises started to produce different types of mind machines and some scientists followed the line of research to explore if and how these devices elicit effects on brain processes. In the late 1980s and early 1990s Farley initiated an