In all sensory processes, some form of energy stimulates a receptor cell in one of the sense organs. The receptor cell converts that energy into a neural signal, which is further coded as it travels along sensory nerves. By the time it reaches the brain, the message is quite precise.

The energy reaching a receptor must be sufficiently intense to produce a noticeable effect. The least amount of energy needed to generate any sensation at all in a person 50 percent of the time is called the absolute threshold. The difference threshold or the just noticeable difference (jnd) is the smallest change in stimulation that is detectable 50 percent of the time. Generally speaking, the stronger the stimulation, the bigger the change must be to be sensed. According to Weber’s law, the jnd for a given sense is a constant fraction of the original stimulus. In most cases, our senses adjust to the level of stimulation they are experiencing, a process known as adaptation.

Subliminal messages are messages that fall below the threshold of conscious perception and are therefore assumed to be perceived subconsciously. Some studies have indicated that, in a controlled laboratory setting, people can be influenced briefly by sensory messages that are outside their conscious awareness. No scientific studies support the claims, however, that subliminal messages in advertising influence consumer choices or that subliminal phrases in self-help tapes significantly change a person’s behavior.