A coded summation method to measure evoked responses of human beings

Human Beings have several kinds of responses evoked by different kinds of stimuli. Examples include auditory evoked responses, visual evoked responses, and etc. Evoked responses appear in electroencephalograms (EEGs) and are measured by an EEG. These evoked responses have a smaller amplitude wave and an averaged summation method (ASM) is widely used to measure this phenomenon. The ASM, however, is not entirely suitable to measure a signal hidden behind nonstationary data with a high ratio. Because the number of average summation cycles has to increase in order to improve the signal-to-noise ratio, increased time is required to measure a signal. The nonstationarity of data also increases the danger that a measured signal has several distortions caused by nonstationarity. These facts indicate the necessity for a short period measurement to obtain an evoked response. At the same time, the short period measurement realizes a reduction of load for measured person. In this paper, a process called a coded summation method (CSM) is proposed. This method has the ability to measure an evoked response within 1/4, approximately 1/12 of the time that is required by the usual ASM. The CSM transforms the original data into codes and then follows with a summation and an averaging for the coded data. The CSM is applied to two kinds of actual cases; the measurement of auditory slow vertex responses and visual evoked responses. Through the trials and discussions about the results in these two cases, an algorithm is derived to determine several CSM parameters the effectiveness of CSM is evaluated by being compared with the traditional ASM technique.