\begin{table}%t2a
\caption{The frequency distribution of $\Delta\alpha$.}\label{tab2a}
%\centering
\par
\begin{tabular}{ c c cccccccc }
       \hline \hline
 ~~~ & $|\Delta\alpha|$( ms ) & 00--05 & 05--10 &10--15 & 15--20
           & 20--25 & 25--30 & 30--35 & ~~$>$35~~ \\
       \hline
 Hipp        &  N  & 3710  & 1553  & 537  & 214  & 93 & 38 & 11  & 0   \\
 ~           & \%  & 60.3  & 25.2  & 8.7  & 3.5  & 1.5& 0.6& 0.2 & 0   \\
 CAMC4       &  N  & 156   & 123   &  88  &  72  & 39 & 31 & 18  & 24  \\
 ~           & \%  & 28.3  & 22.3  & 16.0 & 13.1 & 7.1& 5.6& 3.3 & 4.4 \\
       \hline
 \end{tabular}
\end{table}