EEG signal analysis preprocessing

[sadatwins]

hello
i was if it is possible that you can help me in my project i was planning to make a device that is controlled using BCI
but i am stuck with the analysis and i have a few questions that i would like to ask?
i was implement this paper "CLASSIFICATION OF MENTAL TASKS FROM EEG SIGNALS
USING EXTREME LEARNING MACHINE"

1)The EEG signals are first normalized with zero mean and variance one,and then divided into half-second segments with an overlap of one-quarter-second between adjacent segments.
about the above why i should normalize ?and how can i ?what am i normalizing
2)is there some book that can help me in the analysis or any other reference

 

[BradtheRad]

In digital audio terminology, to normalize means to remove DC component. What remains is AC data, centered around a zero reference.

It's done because electronic components handling AC signals are not necessarily adjusted to be free of DC offset.