Initiation of sinusoidal tracking eye movements in man.

Smooth pursuit eye movement was recorded with a DC amplifier during horizontal sinusoidal target motion at 0.3, 0.6, 0.8, 1.0 and 1.2 Hz and a peak-to-peak amplitude of 20 degrees. Eye movement was digitalized at 100 Hz and 12 bits. From the digitalized eye movements, the maximum position error, the correlation coefficient and regression coefficients between stimulus and eye position were calculated in each half cycle. The A/D conversion and calculation were performed using a 16 bit microcomputer (NEC PC 98). Thirteen healthy volunteers with normal smooth pursuit patterns were examined. The correlation coefficient increased, but the maximum position error and the two regression coefficients decreased as the target moved. However, all four stabilized from about the 3rd half cycle regardless of the target frequency. These findings indicate that the smooth pursuit of a sinusoidally moving target reaches the maintenance at about the 3rd half cycle after initiation of two half cycles from the beginning of the target motion. This might be due to a prediction (or learning) of periodicity.