investigation concerning medical claims made by some manufacturers and sellers. The FDA concluded that Light and Sound Machines were not medical devices and did not warrant regulation. Sellers and manufacturers were given guidelines for how they could advertise these devices, and were required to include a disclaimer and cautionary document with each machine. Nowadays, mind machines are rediscovered by some teenage cultures as so called “digital drugs”, a legal way to enter altered states of consciousness. Application Mind machines include flashing light devices, which are similar to the Brion Gysin dreamachine in that both produce a flickering visual field. Unlike flashing light devices, the dreamachine can be used by several people at once, but has few, if any, technical features. Technical setting Mind machines typically consist of a control unit, a pair of headphones and/or strobe light goggles. The unit controls the sessions and drives the LEDs in the goggles. Professionally, they are usually referred to as Auditory Visual Stimulation Devices (AVS devices). Also mind machines are offered that can connect to the Internet for updates download of new session material. Application rate One session normally takes between 15 and 60 minutes. During a session the user should lie relaxed, and place the glasses on the eyes, which should remain closed during the whole session. Many machines have pre-programmed sessions which vary in parameters like light brightness, audio pitch or beat frequency but also give the opportunity for the user to create a custom session. Typically one session consists of a series of segments. Within one segment parameters change in a constant way. Mind machines are often used together with biofeedback or neurofeedback equipment in order to adjust the frequency on the fly, while proof for their effectiveness is lacking. Description of altered states Perceptual changes Light & sound mind machines can have various effects on the user. Most users describe seeing a flashing light, others perceive swirling patterns that have been compared to psychedelic light shows or fractals. A few users report seeing detailed, virtual reality like scenes. But also tactile and emotional changes are reported after a 6 Hz photic stimulation, as well as auditory hallucinations like binaural beats. Changes in brain activity Sessions will typically aim to address the target frequencies which correspond to delta (1-3 hertz), theta (4–7 Hz), alpha (8–12 Hz) or beta brain waves (13–40 Hz). Those frequency bands can be adjusted by the