This is my current code:
\newcolumntype{b}{X}
\newcolumntype{m}{>{\hsize=.5\hsize}X}
\newcolumntype{s}{>{\hsize=.2\hsize}X}
\begin{table}
\caption{Summary of the Most Common BCI Control Signals}
\centering
\begin{tabularx}{\textwidth}{sbmmsbb}
\hline
\textbf{Name} & \textbf{Phenomena} & \textbf{Type} & \textbf{No. commands} & \textbf{Training} & \textbf{Advantages} & \textbf{Disadvantages} \vspace{4pt}\\
\hline
SSVEP & Oscillatory signals at the same frequency than a flickering visual stimuli & Exogenous & High & No & Very high transmission rates \newline No training required & Possible visual fatigue and epileptic seizures \newline No. commands limited by the standardized refreshing rate of LCD screens \newline Requires gaze control\vspace{4pt}\\
\hline
\end{tabularx}
\end{table}
I want to horizontally center the row in order to get something like this:
Any ideas?
EDIT: Now I can center the rows using \renewcommand\tabularxcolumn[1]{m{#1}}, but I cannot modify the percentage of widths using \newcolumntype{m}{>{\hsize=.5\hsize}X} because it does not compile. Any solution to have both at the same time?



\newcolumntype{a}{>{\hsize=.5\hsize}X}will work. If you include\renewcommand\tabularxcolumn[1]{m{#1}}into your document, anmtype column (vertically centered, fixed width, automatical linebreaks) is already defined, so using\newcolumntype{m}will lead to an error. – leandriis Jan 11 '19 at 11:27