This is a sophisticated and powerful tool for the analysis and feedback of EEG signals. It amplifies the signals, analyses them, and provides a visual display of the amplitude of five different frequency bands. It also provides sound feedback for the presence of signals in a specified frequency band; it times for how long they are present in a timed training session, and warns of the presence of unwanted signals and of muscle activity.

It can pass data to a computer for subsequent analysis, and can switch on a battery-operated audio player to give your personal selection of feedback sound.

It represents a major advance in EEG equipment at a very reasonable price. While much more expensive than the Alpha Sensor, its microcomputer control and elaborate filter system and particularly its capacity to look at more than one frequency at a time make it technically far superior. Other multi-frequency EEG systems start at at least twice the price of this one.

The instrument is operated from 6V DC, from batteries or a mains power supply. A headband with gold-plated electrodes is supplied as standard and other electrodes can be provided. Highly discriminating filters separate the signals into the following wavebands:

• Theta, 4-6Hz;
• Alpha I, 7-8Hz;
• Alpha II, 9-11Hz;
• Alpha III, 12-13Hz;
• Beta, 13-30Hz.

A separate channel detects muscle (EMG) activity in the range 100-300Hz. For each channel including EMG there is a LED bar graph display, with a sensitivity switch to extend its range. For the channel selected for feedback, amplitude is shown digitally.

Separate quantitative indicators show if electrode contact is poor and if artifact is present; only if they are not, and if the signal exceeds the adjustable threshold, can feedback be obtained. The feedback takes the form of a pleasant chirping sound, presented either through the loudspeaker or an earphone. The instrument notes the amount of time during which feedback is supplied, and at the end of the preset session time, 3 to 30 minutes, the 'score' of time above threshold is displayed digitally, alternating with the session time.

As the EMG Channel can register up to 250 µV, the instrument can also be used specifically for EMG feedback. During training, data is passed to an RS232 connector; many computers can accept such a signal.

Specification

• Power: 6V 600mA DC
• Input impedance: 10 megohm Filter band centres: 5, 7.5, 10, 12.5, 22, 200Hz
• Thresholds: 5, 7.5, 10, 20, 30 µV p-p.
• Level Indicators:
  • EEG: 0-25 and 0-50 µV p-p
  • EMG: 0-50, 0-100, 0-250 µV rms
• Controls: Power, Full Scale 25/50, Filter Select, Threshold Level, Volume, EMG Range, Start/Stop training session.
• Displays: Power; Sensor contact; Artifact; Time; RS232 active; Bar Graph Amplitude, for each waveband; Digital Amplitude, for chosen waveband; Waveband selected
• Dimensions: 300 x 180 x 60mm
• Weight: 2.5kg. Metal case.