Quantitative Evaluation of Pursuit Eye Movements with Frequency Analysis

Abstract

A method of quantitatively evaluating discontinuity in pursuit eye movements (PEM) using spectral analysis is proposed. In this method, comparison of the measured values under various stimulus frequencies (FSs) was considered possible. The power ratio (PR) that represented the degree of mixing of discontinuous component into PEM was calculated. The lower limit of the range for spectral analysis was the FS. The upper limit was defined assuming the following model. PEM mixed in the discontinuous components was considered to be a wave composed of synchronized sine and rectangular waves with frequencies equal to FSs. The rectangular wave was composed of the sine wave with elementary frequency and its odd harmonics. The upper limit was defined as follows; on all FSs, the same number of odd harmonics existed within the nyquist frequency. The denominator of PR was the total power of the range for spectral analysis described above. The numerator was the total power between the frequency of the third harmonic and the upper limit of the range for spectrum analysis.
The horizontal PEM was measured in six adults aged 22 to 37 years old and six preschool children aged five years old, whose PEM did not reach the adult level. FSs were 0.3-, 0.5-, 0.7-Hz and the amplitude of stimulus movement was ±17.5° visual angle. For both groups, PEM became less smooth with increased FSs, and there was a significant increase in PR. At all FSs, PRs of children were significantly higher than those of adults. This finding suggests the validity of this method.