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Justin Keogh
03-21-2001, 05:30 PM
0100,0100,0100Dear list,


We have collected some EMG (1000 Hz), accelerometry (100 Hz)
and video (50 Hz) data in a recent study. We seek to investigate
the relationships between these variables in the frequency
(coherence) and time (cross-correlation) domains.


Papers which have done EMG-tremor coherence (Halliday et al.
1999; Marsden et al. 1997; Vaillancourt et al. 2000) have all
sampled their different sources of data at the same rate. While we
would have liked to do that as well, that was not possible.


Therefore we need to resample our data so to obtain the same
number of data points, and to ensure that these data points were
measured at the same point of time.


So my questions are thus:


1. Is it better to downsample the data (eg EMG from 1000 to 100
Hz) or upsample tremor from 100 to 1000 Hz?

2. We have noticed a change in the power of the resampled data in
proportion to the change in signal sampling frequency. Is this a
problem for coherence and cross-correlation analyses?


Any other comments or papers to refer to would be appreciated.


Thanks,


Justin Keogh.


References

Halliday, D. M., Conway, B. A., Farmer, S. F., & Rosenberg, J. R. (1999). Load-
independent contributions from motor-unit synchronization to human
physiological tremor. Journal of Neurophysiology, 82, 664-675.


McAuley, J. H., Rothwell, J. C., & Marsden, C. D. (1997). Frequency peaks of
tremor, muscle vibration and electromyographic activity at 10 Hz and 40 Hz
during human finger muscle contraction may reflect rhythmicities of central
neural firing. Experimental Brain Research, 114, 525-541.


outVaillancourt, D. E., & Newell, K. M. (2000). Amplitude changes in the 8-12, 20-25,

outand 40 Hz oscillations in finger tremor. Clinical Neurophysiology, 111, 1792

out-1801.




Justin Keogh BHMS (Hons)
PhD Candidate
Griffith University, Gold Coast
School of Physiotherapy & Exercise Science
07 5552 8390 (W) 0419 714 921 (M)
07 5552 8674 (Fax)
justin.keogh@mailbox.gu.edu.au

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