Participants were required to detect spot stimuli briefly presented to the upper, central, or lower visual fields. The stimuli were presented either on a green or a red background. Results showed that reaction time (RT) was shorter for the lower visual field (LVF) compared to the upper visual field (UVF). Furthermore, this LVF advantage was significantly reduced in the red background condition compared to the green one. A red light is known to suppress activity of the magno-dominated stream. Therefore, the LVF advantage in RT can be explained as resulting from the biased representation of the magno-dominated stream in the LVF.