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Two backward masking experiments were carried out. In Experiment 1, the test pattern was one or two vertical lines and the mask stimulus was a large rectangle flash pattern or four small rectangle flash pattern. Three subjects reported how many lines were presented. In Experiment 2, three symbols (English alphabet letters or Chinese ideographs) were successively presented on the same position of the CRT display. Four subjects reported the name of the first symbol. Experiment I revealed that the response latency of feature extraction stage in the human visual system was about 50 ms. Experiment 2 showed that in the feature extraction stage the time required for processing a symbol was about 60-70ms. The results indicate that feature extraction processing is parallel, that is, it extracts two or more line segments in the same time, and that feature extraction processing for a symbol is completed about 80-100 ms after the onset of the symbol presentation to the retina.