EEG Signal Digitation Rate

Using an interface set up between the amplifiers and the computer, the EEG signals are fed into the analog/digital (A/D) converter in the computer. The computer converts the analogic variations in potential into a series of discrete digits with a given digitation rate as a function of time. What characterizes the strength of ERPs is their high temporal resolution, which allows the faster sensory processing of the brain to be investigated without any time lag. For example, a digitation rate of 512 Hz indicates that over a time span of 1 sec the potential value is sampled about once every 2 msec. In some cases, such as in recording auditory brain stem potentials, which reach the primary projection cortex in 10 msec, even a sampling rate of 1 or 0.5 msec may be utilized. The set of sampled points may thus be stored in the mass memory or on the hard disk (HD) of the computer and subsequently displayed and analyzed in the form of continuous oscillating signals (EEG) using dedicated graphics display software. A/D conversion should be carried out at a rate that is sufficiently rapid to allow those frequencies that reflect the EEG and ERP signals of interest to be properly recorded. The A/D conversion rate, as well as the amplifier filter set up in terms of low and high cutoff frequencies, should always be specified in scientific reports (Picton et al., 2000).

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