Abstract
Objective: VEPs elicited by low spatial frequency and low contrast stimuli were recorded to investigate the function of the magnocellular system in normal subjects. Methods: Healthy six adults and five children participated in this study. Black and white sinusoidal gratings with spatial frequency of 0.28 c/deg and reversal rate of 15 rev/ sec were presented through CRT monitor to each subject. Results: Substantial VEP responses were recorded at Oz with 30% contrast stimuli in most subjects. Peak to trough amplitudes were decreased linearly as the decreasing of the contrast from 30% to 10%. Contrast thresholds which are obtained by extrapolating the regression lines to 0 lV, were 2.6% to 3.1% for adults and 2.7% to 4.2% for children. Conclusion: Low contrast, low spatial frequency stimuli were reported to be optimal to activate magnocellular system. Therefore, VEPs in the present study may reflect the function of such specific visual system in control subjects. Further research is needed to record more stable responses, especially in children, to estimate normal contrast thresholds.
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