It has recently been shown that noise can facilitate signal detection in the sensory systems. We have previously shown that contrast detection sensitivity in the visual perception is improved in the presence of noise by measuring the detection threshold (Sasaki et al. Effect of noise on the contrast detection threshold in visual perception, Neurosci. Lett. 408 (2006) 94-97). In the present study, we reexamined the previous findings by measuring the percent correct detection rates in a two-alternative forced-choice (2AFC) paradigm and examined further whether the addition of noise improved the discrimination of the visual patterns. In the first experiment, the addition of weak noise facilitated the detection rate, thus confirming the previous findings. Furthermore, a significant correlation between the control detection rate without noise and the noise intensity that induced the maximum facilitation of the detection rate was found. In the second experiment, the addition of a subthreshold noise facilitated the discrimination of visual patterns. These results showed that the effect of noise that induces facilitation in signal detection is robust regardless of the methods used for measuring the detection sensitivity, and that pattern discrimination can also be improved by the addition of noise.