Also known as light and sound stimulation, AVS systems use flashing lights (usually small lights set inside eyeglasses) and sound (usually through a set of earphones) to entrain the EEG. Various forms of AVS devices have been in use both clinically and commercially since the mid-1970s and currently there are a number of different manufacturers (mostly American) who make this type of equipment and sell codeine phosphate 30mg these machines to the public (e.g., Comptronics Devices Ltd., Microfirm Ltd., Mind Gear Devices Ltd., Synetics Systems Inc, Zygon Inc., etc.).
Basically, all commercially-available AVS devices are relatively small and portable electronic devices which will stimulate the user with flashing light through a special set of eyeglasses and with sound through the earphones. Like the EDS system, the light stimulation from AVS devices is given by means of a set of special eyeglasses with small lights built into the back of the lenses. The sound stimulation usually consists of simple beats or pulses of sound generated for the user through a set of earphones. Generally, the light and sound stimulation are designed to be syncopated so as to increase the EEG entrainment effect.
Unlike EEG biofeedback systems or the EDS system, commercial AVS devices do not record the user’s brain waves or show the user what is happening to the EEG while the device is being used. Also, unlike the EDS system, AVS devices are not interactive- that is, the stimulation coming from the AVS device does not change with changes in the user’s EEG. AVS devices are usually preprogrammed to run some number of different stimulation sessions, each varying in the pattern of frequency changes of the lights and sounds over the course of the session.
In most cases, commercial AVS devices include some limited number of different stimulation sessions pre-programmed into the device memory chip. Each of the different sessions are usually designed to entrain the user’s EEG in some specific segment of the total EEG spectrum so as to achieve some specific mind state. For example, most of these devices include programs that are designed to entrain the EEG into the alpha frequency range (8-12 Hz) which is generally associated with feelings of relaxation, or into the delta frequency range (1-4 Hz) which is generally associated with deep, restorative sleep, or into the beta frequency range (above 12 Hz, usually 16-24 Hz stimulation) which is generally associated with alert wakefulness and focused attention.