The present study examined the practice effect of backward pattern masking in the context of recent researches on perceptual learning. On the discrimination task, thresholds decreased substantially with practice. In addition, the practice effect was specific to the mask pattern. In contrast, it cannot reasonably be assumed that the practice effect was specific to the eye and the retinal position. These findings suggest that practice diminished the interruption of processing in capacity-limited processing. In addition, the specificity of the practice effect to the mask pattern suggests that participants learned to filter out the specific type of mask from capacity-limited processing. On the detection task, thresholds decreased with practice. But the improvement was smaller on the detection task than on the discrimination task. It may be assumed that the practice effect on the detection task does not involve a decrease in the effect of the interruption in capacity-limited processing.