Spectral analysis of human tremor during cognitive tasks.

Many stresses occur in our daily lives. Some of these are part of diseases of the nervous system such as ataxia and neuroses. Certain body tremors may be related to these stresses. The rhythmic movement of various muscle groups, similar to a fast circadian rhythm, is defined as a tremor. These tremors, occurring during cognitive tasks, have been recorded by one-dimensional accelerometer in use in our laboratory. In this expanded study, we recorded three-dimensional body displacements with an optical motion capture system while subjects were performing the tasks of intent listening, reading and mental arithmetic calculations. The recorded displacements were subjected to spectral analysis using the Fast Fourier transform (FFT). The results indicate that the body vibration amplitude spectrum caused by mental arithmetic is significantly increased in the frequency rage of 0.5 to 0.7 Hz, when compared to those recorded during other tasks. The induced tremor, as well as general invisible body micro-vibration, were obtained from the three-dimensional body displacements.