Lower sampling rates have been found to provide sufficient data for use in the method of U.S. Pat. Nos. 7,071,831, 7,616,125 and 7,791,491. The method of determining drowsiness includes the steps of receiving eye movement data collected at sampling rates as low as 20 Hz. The data is preferentially interpolated to provide a data set at a higher sampling rate in the order of 500 Hz. For each data point, values of amplitude and velocity of eye movement and whether the measures relate to eyelid opening or closing are derived. An algorithm is then used to obtain values of the amplitude to velocity ratios of eyelid opening and closing and using these values in an algorithm for providing a measure of drowsiness. With this method eyelid and eye movement may be monitored using any suitable technology or sensor including video or digital camera technology to identify and measure the appropriate ocular movements.
