Independent Component and Spectrum Analyses for Saccadic Eye Movements

• Main Authors: Tzung-Yuan Lee, 李宗原
• Other Authors: Tainsong Chen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/30276236586704540142

碩士 === 國立成功大學 === 醫學工程研究所 === 91 === The activation and control of eye movements is a complicated process in the central nervous system (CNS), which is proceeded through the coordination of cerebrum, cerebellum, brain stem, and other parts of the brain. For patients suffering from CNS lesions, the pathological changes or degeneration will produce eye movement disorders. Parkinson’s disease is an example. Previous studies showed that the driving signals of saccade generation consist of pulse and step. The pulse component moves the eye to the target position, while the step component makes the eye fixate at the target position. The pulse and step will be abnormal if the neurons responsible for the generation of saccades are degenerated or disordered. If the pulse is not normal, the peak velocity, duration, and saccade overshoot will be affected, while the abnormal step will decrease the accuracy of the saccades since the patients are unable to fixate at the target. Recently the technique of independent component analysis (ICA) has been proposed to separate the underlying components in the signal set. The first goal of this study used ICA to separate the pulse and step components in the recorded saccade profiles. Recording the trajectories of eye movements by Electro-oculogram (EOG) embeds more noise than other techniques, which causes the resolution to be greatly decreased. In addition, the abductive saccades present lower peak velocity than the adductive, which is against the previous investigation and might be caused by EOG artifacts. Therefore, the second goal was to set up an infrared eye tracker system with great precision for eye movement recording, accompanied programs were also designed for target control, target pattern generation, and data analyses. The results of temporal and spectral analyses of the recorded saccadic profiles were compared with the results obtained by previous investigations, which is useful for ascertaining the precision of the recording device. Four subjects (two males and two females) with age ranging from 24 to 26 were recruited for recording saccades by infrared eye tracker in the experiment. The results show that the pulse component dominates the progression of saccades, the pulse amplitude increases with the saccades. The time when the pulse arrived at its maximum intensity was delay by 1 to 2 ms if compared with the time that the peak velocity occurred in the saccadic profile. The results of spectral analysis demonstrates that the local minimum of the power spectrum shifts to lower frequency when the saccade amplitude increases, which indicates that the duration increases with saccades amplitude. Also the reciprocals of the frequencies corresponding to each local minimum were proportional to the durations of saccade. The frequencies corresponding to each local minimum do not follow harmonic relationship, which means that the pulse component of a saccade is actually not a square wave as suggested by some models. The results of spectral analysis match with previous studies, this shows that the infrared eye tracker is capable of recording eye movement profile with great accuracy. Future works will be emphasized on the decomposition of the pulse and the step components of saccades and study their correlation with the neurological disease for the patients.