Mathematics in Independent Component Analysis

268 Chapter 20. Signal Processing 86(3):603-623, 2006
(a)
(b)
mass-EMG
electrode
electrode-array
8 chan.s
direction of muscle fiber
3mm
CH1
1mm
2.54mm
belt
strain gauge
CH8
41mm
2.54mm
41mm
chair
styrofoam
cast
oscilloscope
measured
torque target
torque
Fig. 3. Experimental setting; (a) Eight-channels s-EMG was recorded during an
isometric, constant force 30% of subject’s MVC. (b) Detail of the s-EMG bipolar
electrode array used for the recordings.
Eight-channel EMG bipolar signals were measured (input impedance above
10 12 Ω, CMRR of 110 dB), filtered by a first-order, band-pass Butterworth filter
(cut-off frequencies of 70 Hz and 1 kHz), and then amplified (gain of 80
dB). The target torque and the measured torque were displayed on an oscilloscope
as a thick and as a thin line respectively, which the subject was asked
to match. The eight-channel s-EMG was sampled at a frequency of 10 kHz, 12
bits per sample, by a PCI-MIO-16E-1 A/D converter card (National Instruments,
Austin, Texas, USA) installed in a PC, which was also equipped with
a LabView (National Instruments, Austin, Texas, USA) program in charge of
controlling the experiments. The signals were recorded during a 5s period of
constant-force isometric contractions at 30% maximum voluntary contraction
(MVC).
Before applying any BSS method, the signal was preprocessed using a modified
dead-zone filter developed to retain the MUAPs belonging to the target
MUAPT and to remove both noise and low-amplitude MUAPs that did not
reach the given thresholds. The nonlinear filter is realized by an algorithm that
was developed in order to retain the MUAPs belonging to the target MUAPT
and to remove both the noise and the low-amplitude MUAPs that did not
reach the given thresholds. In former works, these thresholds were initially set
at a level three times above the noise level (recording at 0% MVC) and then
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