A number of previous studies have extensively investigated directional anisotropy in motion perception. However, consensus has not been reached regarding the nature of motion directional anisotropies in human vision. In this study, we investigated the directional anisotropy of human motion perception by moving random-dot stimuli in the peripheral upper visual field. Our findings show that the degree of directional anisotropy depends on the stimulus speed. Furthermore, the high and low speed conditions have preferred directions that are opposite. This may reflect differences in the directional information among temporal frequencies in natural scenes. These differences are thought to have crucial roles in the detection of motion direction. (C) 2010 Elsevier Ltd. All rights reserved.