It is not certain what physical, chemical or neural mechanism causes or generates the changes in air pressure in or near the ear in response to various thoughts. It is hypothesized that various thoughts have varying intensities which cause involuntary muscle contractions or movements on a microscopic level in or near the ear, which generate pressure changes in or near the ear due to the compression of the air local to the ear. Nevertheless, regardless of the exact physical, chemical or neural mechanism, empirical testing has confirmed that thoughts generate small pressure changes in or near the ear of the person having the thoughts and that the air pressure changes have substantially their own signature and are thus substantially unique for each type of thought. Consequently, the air pressure changes can be monitored near the ear and used to detect the presence and type of thoughts of a user.
…according to US Patent 6,024,700, anyway.