Modern society and lifestyles impose severe stresses on human beings, young and old from all walks of life. Medical researches had demonstrated with ample proofs that prolonged stresses, whether physical, mental or emotional, can adversely impact a person's health and well being.
In modern society, electromagnetic field (EMF) pollution is becoming severe and widespread, as electrical appliances and electronic devices becoming pervasive in our workplace, home and environment. As most appliances and devices draw their power from the power grid (60Hz or 50Hz depending on your country), power line related (i.e. power transmission network as well as power-drawing equipment and devices) noises are most prominent in our living environment.
1. Automatic Sleep Stage Scoring with Wavelet Packets Based on Single EEG Recording by Luay A. Fraiwan, Natheer Y. Khaswaneh, and Khaldon Y. Lweesy in World Academy of Science, Engineering and Technology 54 2009
2. Performance of the frequency domain indices with respect to sleep staging by Terry B.J. Kuo a,b,c, C.Y. Chen a,b, Ya-Chuan Hsu a,b, Cheryl C.H. Yang in Clinical Neurophysiology Volume 123, Issue 7 , Pages 1338-1345, July 2012
3. EEG Analysis Applied to Sleep by Peter Achermann, Epileptologie 2009; 26: 28 – 33
Low cost motion sensors usually deploy 3-dimensional (3D) accelerometers to track the motion and activities of the user. The sensor monitors the acceleration (including gravity), so it can detect real motions (with significant acceleration) as well as change in orientations (or postures). The motion sensor is usually attached to head, body trunk, or on limbs. Running, jogging, walking are easily tracked to provide pedometer or equivalent functionality. It's also very effective in detection of "dozing off" when the subject is drowsy and goes into micro-sleep episodes.
Skin Conductance Response (SCR) is also called Galvanic Skin Response (GSR). The SCR increases whenever there's excitation or emotional response, and the stronger the response the stronger the SCR signal. Being surprised, strong emotions, strong pain and laughing heartily can readily produce strong SCR signals. The SCR signal consistently rises within 1~3 seconds, and relaxed out over longer periods (4~10 seconds). SCR is part of the polygraph test and is commonly used in market research to determine the true emotional response level of the subject.
ECG (also called EKG) signal measures the electrical control signals from the sympathetic and para-sympathetic nervous systems that regulate heart beat. If measured at suitable location, it also provides useful signals on inhaling (excitation) and exhaling (relaxation) phases of breathing. For medical diagnoses and treatments, please be directed to medical professionals. Here we only provide simplified descriptions.
Sleeping is the most essential and longest duration human activity, yet we know very little of the wonderful rhythms in us. We will not address any medical diagnoses nor treatments here, they need to be directed to medical professionals. We simply describe the commonly accepted sleep stages (called hypnogram), please see references such as Wikipedia for more detailed descriptions.
Sleep stages are classified as 1. Wake, 2. Drowsy, 3. Sleep I (shallow), 4. Sleep II, 5. Slow Wave (Sleep III & IV) and REM sleep, generally according to EEG signals.
Human is a marvelously adaptive creature, and many of our capabilities remain hidden and not well understood. Bio-feedback generally refers to the training of our body, mind, heart to learn, adapt and control specific stimuli from any or a combination of our senses. Bio-feedback may have been achieved or learned consciously, but also quite often achieved subconsciously or unconsciously.
Both dry electrodes and gel electrodes are commonly used for EEG, ECG, EMG, SCR measurements. Dry electrodes are durable, easy to use and easy to clean, while adhesive gel electrodes generally make more stable skin contacts, but may need replacement after repeated use.
There is really no mystery, nor needing expensive ingredients to get good skin contacts. Remember, human body is essentially a saline bag (just water, salt, and tissues), so most saline solution or gel are all very compatible with it.