TABLE 1.

Applied spatial filters.

Name	Description	Electrode configuration			Matrix (S)
TSD	Single differential filter in transverse direction with large inter-electrode distance (i.e. center to center inter-electrode distance of 30 mm)	1•	•−1		$\left[\begin{array}{ccc}1\hfill & 0\hfill & -1\hfill \end{array}\right]$
LSD	Single differential filter in longitudinal direction with large inter-electrode distance (i.e. center to center inter-electrode distance of 30 mm)	1•			$\left[\begin{array}{c}\hfill 1\hfill \\ \hfill 0\hfill \\ \hfill -1\hfill \end{array}\right]$
		−1•
BipD	Single differential filter in diagonal direction (i.e. center to center in ter-electrode distance of around 21 mm)		1•		$\left[\begin{array}{cc}\hfill 0\hfill & \hfill 1\hfill \\ \hfill -1\hfill & \hfill 0\hfill \end{array}\right]$
		−1•
BipRD	Single differential filter in reverse diagonal direction (i.e. center to center inter-electrode distance of around 21 mm)	1•			$\left[\begin{array}{cc}\hfill 1\hfill & \hfill 0\hfill \\ \hfill 0\hfill & \hfill -1\hfill \end{array}\right]$
			−1•
BipT	Single differential filter in transverse direction (i.e. center to center inter-electrode distance of 15 mm)	1•	•−1		$\left[\begin{array}{cc}1\hfill & -1\hfill \end{array}\right]$
BipL	Single differential filter in longitudinal direction (i.e. center to center inter-electrode distance of 15 mm)	1•			$\left[\begin{array}{c}\hfill 1\hfill \\ \hfill -1\hfill \end{array}\right]$
		−1•
DDT	Double differential filter in transverse direction	−1•	2•	•−1	$\left[\begin{array}{ccc}-1\hfill & 2\hfill & -1\hfill \end{array}\right]$
DDL	Double differential filter in longitudinal direction	−1•			$\left[\begin{array}{c}\hfill -1\hfill \\ \hfill 2\hfill \\ \hfill -1\hfill \end{array}\right]$
		2•
		−1•
LapD	5-point Laplace filter		−1•		$\left[\begin{array}{ccc}\hfill 0\hfill & \hfill -1\hfill & \hfill 0\hfill \\ \hfill -1\hfill & \hfill 4\hfill & \hfill -1\hfill \\ \hfill 0\hfill & \hfill -1\hfill & \hfill 0\hfill \end{array}\right]$
		−1•	4•	•−1
			−1•
IR	Inverse rectangle filter	−1•	−1•	•−1	$\left[\begin{array}{ccc}\hfill -1\hfill & \hfill -1\hfill & \hfill -1\hfill \\ \hfill -1\hfill & \hfill 8\hfill & \hfill -1\hfill \\ \hfill -1\hfill & \hfill -1\hfill & \hfill -1\hfill \end{array}\right]$
		−1•	8•	•−1
		−1•	−1•	•−1
IB2	Inverse binomial filter of order 2	−1•	−2•	•−1	$\left[\begin{array}{ccc}\hfill -1\hfill & \hfill -2\hfill & \hfill -1\hfill \\ \hfill -2\hfill & \hfill 12\hfill & \hfill -2\hfill \\ \hfill -1\hfill & \hfill -2\hfill & \hfill -1\hfill \end{array}\right]$
		−2•	12•	•−2
		−1•	−2•	•−1