matstruct = load('YourEEGFile.mat');
eegvals = matstruct.NameOfYourInputVariable;
num_eeg = length(eegvals);
num = xlsread('YourPositionFile.xls');
spos = num(:,1);
epos = num(:,2);
scores = num(:,3);
last_scored_pos = max(epos);
group_num = zeros(last_scored_pos, 1);
for K = 1 : size(spos,1)
group_num(spos(K) : epos(K)) = scores(K);
end
%there might have been entries in the score matrix that went beyond the actual number of eeg values
if last_scored_pos > num_eeg
group_num(num_eeg+1 : end) = [];
end
Now you have your eegvals matrix, and you have a group_num vector that indicates which group the corresponding entry corresponds to. There may be entries of 0 in the group_num vector so be careful with your assumptions.
You did not indicate how you want to group your data according to the score, so I will end here.