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A. Fernandez–Villa, M.L. Rosenberg; A Revisit Of Different Methods For Estimating Saccadic Velocities And Accelerations . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2492.
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To evaluate a suggested method for evaluating the peak velocities and accelerations of saccades.
We recorded 8 normal subjects at 240 Hz using infra–red videooculography with an accuracy to 0.1 degrees. Each subject performed over 1300 horizontal saccades at amplitudes varying from 5 to 20 degrees. Saccades with blinks within 100 msec of the saccade as well as those glissadic components greater than 25% of the total saccade were eliminated. This left more than 150 saccades for each subject. Peak velocity, acceleration and deceleration were evaluated using different methods. These include the standard method of a backwards difference, central difference (the most commonly used estimating algorithm), and an 8th order approximation utilizing FIR filters. The main sequences generated were compared for each subject.
All calculations using backwards difference was decreased compared to other methods. Central difference showed a consistent decrease in velocity, averaging 15deg/sec less than that calculated by our approximation. More significant was the difference found in the absolute accelerations. The differences averaged 10000 deg/sec/sec. These were consistent amongst all subjects. Deceleration differences were similar.
The method of estimating saccadic velocities have a significant effect on peak velocity but a much greater effect on measurements of acceleration and deceleration . As people analyze acceleration and deceleration as an important part of the analysis the method of estimation becomes critical. We recommend the use of higher order approximating algorithms such as the 8th order approximation used here. We did not evaluate other approximations due to limitations of our mathematical software.
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