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Purpose: Our purpose was to investigate the changes in the dynamic property of vergence eye movements caused by changes in the co-existing stationary background in the central visual field. Methods: Disparity-driven target movement was presented virtually by a head-mounted liquid-crystal display. Two targets were used: a bar-shaped target that moved between 2 and 0.5 m along the mid-sagittal line at a speed of 50 cm/s (vergence target) and a background image of a cross-shaped target that stayed at a distance of 2 m (background target). Eight normal subjects participated in the experiments. The subject was asked to follow the vergence target while the configuration of the background target was randomly changed among four conditions in each experiment: the length (experiment 1) or the width (experiment 2) of the horizontal and vertical lines composing the cross of the background target was each randomly changed among four conditions. A limbus tracker was used to measure eye movements. Results: In experiment 1, there was a negative correlation between the amplitude of the vergence eye movements and the lengths of the lines of the cross in each of five subjects (mean r = 0.018, n = 48 in each subject). Similarly, in experiment 2, there was a negative correlation between the amplitude of the vergence eye movements and the width of the lines of the cross in each of 8 subjects (mean r = –0.12, n = 48 in each subject). Conclusion: The vergence response to a target object significantly differs depending on the texture of background objects on the visual axis.

Purpose: The functional organization of the human cerebellum involved in saccadic eye movements was investigated using functional magnetic resonance imaging (fMRI). Methods: The subjects were 7 normal volunteers aged 18–34 years. Visual stimuli were back-projected onto a screen placed at the subjects’ feet. The stimulation period of 30 s consisted of a saccade target jumping back and forth horizontally by 20° once per second. The control period of 30 s consisted of a fixed target. The stimulation and control periods were alternated 10 times during the presentation. Functional images were collected with a 1.5-tesla clinical MRI scanner. The significance of activation was determined by Statistical Parametric Mapping (SPM 99) at a threshold of p < 0.001 (uncorrected), and significantly activated areas were superimposed on the T1-weighted images. Results: Significantly activated areas related to visually guided saccades were observed in the cerebellar vermis (declive and folium), in the bilateral cerebellar hemispheres (mainly the superior semilunar lobule) of the cerebellum, in the frontal eye field, in the supplementary eye field and in parts of the parietal lobule of the cerebrum. Conclusion: Our results suggest that the cerebellar posterior vermis and bilateral hemispheres are related to saccades in humans. These results are consistent with neurophysiological data obtained in primates.