Decomposition of Control Signals for Saccade and Vergence Eye Movements Using Independent Component Analysis
John L. Semmlow
Saccade is believed to be the fastest eye movement, which is conjunctive and functions to redirect the fovea of the retina to the object of interest. Vergence, on the other hand, are disjunctive eye movements that two eyes move in different directions, which in turn bring the images of the target for two eyes into their corresponding retinal positions. Main sequence relations have been used for describing the dynamics of the saccadic and vergent eye movements. Saccadic duration is approximately proportional to its amplitude, whereas the peak velocity and amplitude relation could be described as an exponential function with saturation occurred at 30-40o. Main sequence relations are also used for quantitative analysis of vergence eye movements that the peak velocity is significantly smaller than saccades. Fourier analysis has also been used in quantitative investigation of saccades. Unlike the temporal analysis for the main sequence relations, spectral analysis relies on the whole trajectories of saccades. An inverse method was also used by previous investigators to reconstruct the input signal of a saccade from the fourier transform of the padded and mirrored position profile and the impulse response of the system model. In this paper, we present the application of independent component analysis (ica) to decompose the components of saccade and vergence eye movements. The results show that the pulse component is activated before the step for both vergence and saccade, which is consistent with previous findings. Also the effect of accommodative activation can be observed for vergence using ica. In conclusion, ica is useful in decomposing the control components for the saccade and vergence from ensembles of recorded profiles, which provides an alternative method for eye movement investigation.