Behavioral response caused by stimuli with subliminal perception below threshold. Appropriate stimulation acts on various receptors and must reach a certain intensity to cause sensation. The minimum stimulus that just causes sensation is called absolute sensation threshold. Although we can't feel the stimulation below the absolute threshold, it will cause certain physiological effects. For example, sound stimulation below the auditory threshold will cause changes in brain waves and pupil dilation. The minimum amount of stimulus that can just cause physiological effect is called physiological stimulus threshold. The threshold of conscious perception and physiological stimulation are not exactly the same. Generally speaking, the threshold of physiological stimulation is lower than the threshold of conscious sensation. The threshold measured by conditioned reflex method is generally lower than that by oral report method, which may be the threshold of physiological stimulation, not the threshold of conscious feeling; In fact, the formation of temporary neural connections does not necessarily cause feelings.