ИСТИНА

To investigate the processing of visual information, accurate data on the distribution of instantaneous velocities of fixational eye movements are required. While the velocities of microsaccades are well studied, drift velocities have been examined by only a few researchers. Eye movement recordings are noisy and estimating instantaneous velocity is not trivial. This study aimed to obtain histograms of the distribution of instantaneous velocities and to test the hypothesis put forward by Murakami (2004, 2010) that the histogram is well fitted with a Gaussian distribution. Twelve participants fixated the central target for 1000, 2200, or 5000 ms in 82 trials each. The observer's eye movements were recorded with SMI HiSpeed 1250 binocularly (500 Hz frequency). Blinks and saccades have been removed from the raw data. Only fixation intervals longer than 150 ms were analyzed. To estimate the instantaneous velocity, a 15-point second-order Savitsky-Golay filter was used. For each subject, the two-dimensional (horizontal and ·vertical) histograms of instantaneous drift velocities were obtained for all records. The resulting histograms are not well approximated by the Gaussian distribution. The standard deviation estimates range from 1.4 to 4.0 deg/s for different observers.