Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters
Abstract
:Introduction
Methods
Subjects
Eye movement data collection
Signal processing of fixation data
Digital filter design
“A general observation from the best filter list is the increasing prevalence of BW filters at higher sampling rates, ending in a total absence of other filter types at 1 kHz. This can be explained by considering the smoothness of the signal. At higher sampling rates more noise is present in the data. Such high-frequency noise can be more efficiently suppressed by the steeper roll-off of the BW filters compared to the two FIR filters, resulting in a smoother signal…”.
Estimation of filter frequency response
Fourier analysis of fixation before and after filtering
Study of the effects of filtering on temporal auto-correlation
Study of the effects of filtering on positional signal and velocity
Results
Analysis of filter frequency response
Fourier analysis of the unfiltered and filtered signals
Effect of filtering on temporal auto-correlation
Illustration of the Effects of Filtering on Positional Signal and Velocity
Discussion
Conclusion
Data Availability Statement
Ethics and Conflict of Interest
Acknowledgements
Appendix A
EyeLink from SR research
- Run the EyeLink Software on the Host PC.
- Click on Set Options on the Camera Setup page.
- File Sample filter option is now visible.
- Turn it OFF for collecting data Unfiltered, STD for standard filtering and EXTRA for extra filtering.
- Click on Setup.
- Eye Data Filtering option is now visible. See the following screenshot for assistance.
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Filter name | Filter characteristics | Final -3db point |
---|---|---|
Savitzky-Golay (SG) | Window length=23, polynomial order =5 | 75 Hz (74.9) |
Infinite impulse response (IIR) | Butterworth type, Order=7, Cut-off (-3dB) =81 Hz, Zero-phase | 75 Hz (75.4) |
Finite impulse response (FIR) | Number of coefficients, taps = 80, Cut-off (-3dB) = 84 Hz, Zero-phase | 75 Hz (75.0) |
1st filter | 2nd filter | ACF 1 | ACF 2 | ACF 3 | |||
---|---|---|---|---|---|---|---|
χ2= 711.5† | χ2= 604.2† | χ2= 492.1† | |||||
Difference | P-value | Difference | P-value | Difference | P-value | ||
Unfiltered | STD | -1.495 | p<0.001 | -1.361 | p<0.001 | -1.505 | p<0.001 |
Unfiltered | EXTRA | -3.056 | p<0.001 | -2.62 | p<0.001 | -2.505 | p<0.001 |
Unfiltered | SG | -2.44 | p<0.001 | -2.551 | p<0.001 | -2.722 | p<0.001 |
Unfiltered | FIR | -3.875 | p<0.001 | -3.491 | p<0.001 | -3.116 | p<0.001 |
Unfiltered | IIR | -3.94 | p<0.001 | -3.727 | p<0.001 | -3.403 | p<0.001 |
STD | EXTRA | -1.56 | p<0.001 | -1.259 | p<0.001 | -1.000 | p<0.001 |
STD | SG | -0.944 | p<0.001 | -1.119 | p<0.001 | -1.218 | p<0.001 |
STD | FIR | -2.38 | p<0.001 | -2.13 | p<0.001 | -1.611 | p<0.001 |
STD | IIR | -2.44 | p<0.001 | -2.366 | p<0.001 | -1.898 | p<0.001 |
EXTRA | SG | 0.616 | 0.0082 | ||||
EXTRA | FIR | -0.819 | p<0.001 | -0.87 | p<0.001 | -0.611 | 0.0090 |
EXTRA | IIR | -0.884 | p<0.001 | -1.107 | p<0.001 | -0.898 | p<0.001 |
SG | FIR | -1.435 | p<0.001 | -0.94 | p<0.001 | ||
SG | IIR | -1.5 | p<0.001 | -1.176 | p<0.001 | -0.681 | 0.0022 |
FIR | IIR |
Unfiltered | SG Filter | IIR Filter | FIR Filter | |
---|---|---|---|---|
Velocity SD | 120.19 | 29.01 | 23.46 | 23.31 |
Velocity RMS | 209.53 | 24.46 | 5.67 | 5.55 |
Copyright © 2023. This article is licensed under a Creative Commons Attribution 4.0 International License.
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Raju, M.H.; Friedman, L.; Bouman, T.M.; Komogortsev, O.V. Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters. J. Eye Mov. Res. 2021, 14, 1-16. https://doi.org/10.16910/jemr.14.3.6
Raju MH, Friedman L, Bouman TM, Komogortsev OV. Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters. Journal of Eye Movement Research. 2021; 14(3):1-16. https://doi.org/10.16910/jemr.14.3.6
Chicago/Turabian StyleRaju, Mehedi H., Lee Friedman, Troy M. Bouman, and Oleg V. Komogortsev. 2021. "Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters" Journal of Eye Movement Research 14, no. 3: 1-16. https://doi.org/10.16910/jemr.14.3.6
APA StyleRaju, M. H., Friedman, L., Bouman, T. M., & Komogortsev, O. V. (2021). Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters. Journal of Eye Movement Research, 14(3), 1-16. https://doi.org/10.16910/jemr.14.3.6