Method and device for detecting a neural response in a neural measurement
A method for processing a neural measurement obtained in the presence of artifact, in order to detect whether a neural response is present in the neural measurement. A neural measurement is obtained from one or more sense electrodes. The neural measurement is correlated against a filter template, the filter template comprising at least three half cycles of an alternating waveform, amplitude modulated by a window. From an output of the correlating, it is determined whether a neural response is present in the neural measurement.
1. A method for processing a neural measurement obtained in the presence of artifact, in order to detect whether a neural response is present in the neural measurement, the method comprising:
obtaining a neural measurement from one or more sense electrodes, the neural measurement being obtained in the presence of artifact;
correlating the neural measurement against a filter template, the filter template comprising at least three half cycles of an alternating waveform, amplitude modulated by a window; and
determining from an output of the correlating whether a neural response is present in the neural measurement.
2. The method of claim 1 wherein the window comprises a triangular window.
3. The method of claim 2 wherein the triangular window is a standard triangular window of length L comprising coefficients w(n) as follows:
For
L
odd
:
w
(
n
)
=
2
n
/
(
L
+
1
)
for
1
≤
n
≤
(
L
+
1
)
/
2
=
2
-
2
n
(
L
+
1
)
for
(
L
+
1
)
/
2
+
1
≤
n
≤
L
For
L
even
:
w
(
n
)
=
(
2
n
-
1
)
/
L
for
1
≤
n
≤
L
/
2
=
2
-
(
2
n
-
1
)
/
L
for
L
/
2
+
1
≤
n
≤
L
.
4. The method of claim 2 wherein the triangular window is a Bartlett window in which samples 1 and L are zero.
5. The method of claim 1 wherein the window comprises one of a Hanning window, a rectangular window or a Kaiser-Bessel window.
6. The method of claim 1 wherein the window comprises one or more basis functions derived from a sinusoidal binomial transform.
7. The method of claim 1 wherein the filter template comprises four half-cycles of an alternating waveform.
8. The method of claim 1 wherein the filter template comprises half cycles of a sine wave, modified by being amplitude modulated by the window.
9. The method of claim 1 wherein the filter template comprises half cycles of a cosine wave, modified by being amplitude modulated by the window.
10. The method of claim 1 wherein only a single point of the correlation is calculated.
11. The method of claim 10 wherein the single point of the correlation is calculated at a predefined optimal time delay.
12. The method of claim 11 , further comprising determining the optimum time delay when a signal to artifact ratio is greater than one, at which a first or single point of the cross-correlation between the neural measurement and the filter template should be produced, by:
at an approximate time delay between the neural response and the filter template, computing real and imaginary parts of the fundamental frequency of the DFT of the neural measurement;
calculating a phase defined by the real and imaginary parts;
relative to a fundamental frequency of the template, calculating the time adjustment needed to change the calculated phase to π/2; and
defining the optimum time delay as being the sum of the approximate time delay and the time adjustment.
13. The method of claim 11 , wherein the optimum time delay is recalculated prior to every attempted detection of a neural response.
14. The method of claim 11 , wherein the optimum time delay is recalculated in response to a detected change in the user's posture.
15. An implantable device for processing a neural measurement obtained in the presence of artifact, in order to detect whether a neural response is present in the neural measurement, the device comprising:
measurement circuitry for obtaining a neural measurement from one or more sense electrodes, in the presence of artifact; and
a processor configured to correlate the neural measurement against a filter template, the filter template comprising at least three half cycles of an alternating waveform, amplitude modulated by a window; and the processor further configured to determine from an output of the correlating whether a neural response is present in the neural measurement.