A great deal of research has been conducted on the effects of vibration on visual acuity. The human contrast sensitivity function (CSF) has also been studied extensively as a predictor of visual performance under real-world conditions. However, no previous studies have combined the two lines of research and examined the effect of vibration on the CSF. Prior research indicates that increasing rates of vibration correspond to a decrease in traditional measures of visual acuity. However, other studies indicate that motion enhances target detection. The present study examined the effects of vibration upon the CSF and found that vibration lowers the threshold of detection for low spatial frequencies but raises the threshold for high spatial frequencies. A loss of contrast at high spatial frequencies due to retinal "smear" may be the cause of this increase in high spatial frequency thresholds under vibration. Physiological mechanisms of motion detection, direction selectivity, and visual pathways are also discussed. This study may have important implications for aerospace medicine and occupations which demand viewing a target or instrument panel under conditions of vibration.