Subliminal stimuli, contrary to supraliminal stimuli, are any sensory stimuli below an individual's absolute threshold for conscious perception. Visual stimuli may be quickly flashed before an individual may process them, or flashed and then masked, thereby interrupting the processing. Audio stimuli may be played below audible volumes, similarly masked by other stimuli, or recorded backwards in a process called backmasking. Introduced in 1895, the concept became controversial as "subliminal messages" in 1957 when marketing practitioners claimed its potential use in persuasion.