Brain processes underlying visual segmentation have been widely studied, being part of the basic processes underlying perception. However, the underlying constraints on perceptual thresholds, set by neuronal processing, remain unclear. Here, the relationship between human visual performance and brain activity was examined using the backward-masked texture segmentation task. Performance showed dependence on the time-interval between target and mask as well as on the amount of prior practice. Correspondingly, early components of human event-related potentials (ERPs) recorded over occipital electrodes showed strong interactions between target and mask responses, suggesting interference with perception processes when the presented mask interacts with sustained target processing. These interactions, revealing an otherwise undetected extended processing time course beyond the early component of the target response, enabled us to quantify individual neuronal thresholds that closely matched the behavioral thresholds (r = 0.93, p = 0.00003). Furthermore, these neuronal thresholds could be improved by practice, suggesting neuronal mechanisms affected by perceptual learning. Predicting performance level not directly detected in the ERP but rather by further interactions shown here in early stages of the visual hierarchy may have important implications in the study of human perception. Practice seems to reduce the temporal interactions between the successive stimuli, revealing brain processes underlying perceptual learning.