Subvocal Speech Recognition

"Subvocal speech is silent, or sub-auditory, speech, such as when a person silently reads or talks to himself. Biological signals arise when reading or speaking to oneself with or without actual lip or facial movement. A person using the subvocal system thinks of phrases and talks to himself so quietly, it cannot be heard, but the tongue and vocal cords do receive speech signals from the brain."[1]

As early as 1975, researchers have been testing "the feasibility of designing a close-coupled, two-way communication link between man and computer using biological information from muscles of the vocal apparatus and the electrical activity of the brain during overt and covert (verbal thinking) speech."[2]

NASA currently uses small electrodes "placed at the location of the tongue and the side of the throat near the larynx, [that] differentially capture a signal that is the result of the difference between the two. They are processed first by transforming them into a matrix of wavelet coefficients (a special kind of wavelet called a dual tree wavelet), and secondly by using a neural-net to classify that wavelet coefficient matrix to associate a particular pattern with the signal energies that are present in the magnitude of coefficients."[3]

A research group at one university is trying to go further by eliminating the use of implants and instead using EEG to control a subvocal Brain-Computer Interface (BCI). "Over the past [eighteen] years, productive BCI research programs have arisen."[4] Brainwaves can be used to move a cursor on a computer screen, for example. Improving the technology to isolate subvocal speech will provide novel uses.

"Quiet cell phones would be one commercial application; possibly communication between divers, is another. Anyone who needs to use noisy haz-mat suits or work in high-noise environments could benefit from this technology."[5]

So far, capturing the signals requires a device having physical contact with the test subject. Ideally, a system should be developed that can read subvocal and other signals from a distance. A high resolution "radar" would be able to pinpoint the signals in the body and interpret them to model the intended activity. NASA is "developing an entirely new type of sensor that doesn’t even have to touch the body, called a capacitive sensor."[6]

It was in 1996 that I first theorized that something like this might be in development by the military industrial complex and exploited by criminal groups. Upon that realization, I developed the habit of subvocalizing a different PIN number when I'm at the ATM.



[3] Op cit.



[6] Op cit.

For more information, visit CIA Tradecraft at

For more information on BCI, search the Entrez PUBMED journal database