Temporal synchrony is a critical cue for binding attributes processed by separate sensory channels, but it remains controversial how the brain computes synchrony across different attributes. Here we describe our hypothesis, time marker theory, which states that cross-attribute synchrony is not based on simultaneous completion of attribute processing, but on the comparison of salient features (time markers) extracted from sensory signals evoked by the stimulus. This hypothesis was originally proposed to account for an anomaly of visual attribute binding, color-motion asynchrony, and is being developed to explain cross-attribute temporal synchrony in general, including cross-modality judgments.