Signal learning (or classical or conditioning) is the simplest example [of learning without consciousness]. If a light signal immediately followed by a puff of air through a rubber tube is directed at a person's eye about ten times, the eyelid, which previously blinked only to the puff of air, will begin to blink to the light signal alone, and this becomes more and more frequent as trials proceed. Subjects who have undergone this well-known procedure of signal learning report that it has no conscious component whatever. Indeed, consciousness, in this example the intrusion of voluntary eye blinks to try to assist the signal learning, blocks it from occurring.