Off-line computing of slow-phase eye velocity profiles evoked by velocity steps or caloric stimulation

We describe a method to compute the slow-phase eye velocity profile without explicit removal of quick phases. It can be used for off-line analysis of eye movements evoked by angular head velocity steps or caloric stimulation. Zero-crossings of eye velocity from negative to positive values divide the velocity trace into intervals of different length. In each interval, the velocity data points are sorted in an ascending order. The value at the least slope (mode value) is taken as the representative slow-phase velocity for the processed interval. Spline interpolation between the representative points of all intervals results in an envelope that gives an accurate description of the slow-phase velocity over time and is used to determine parameters such as peak slow-phase velocity, time constant etc. The method can easily be implemented on a computer.