Research

It is generally accepted that we possess various levels of consciousness. For example, the state of consciousness while we dream is different from the state when we are awake. Packard has distinguished the consciousness into three levels. 

Conscious-rational level, where people know what is going on, and are able to tell why. The second and lower level is called, variously, preconscious and subconscious but involves that area where a person may know in a vague way what is going on within his own feelings, sensations, and attitudes but would not be willing to tell why. This is the level of prejudices, assumptions, fears, emotional promptings and so on. Finally, the third level is where we not only are not aware of our true attitudes and feelings but would not discuss them if we could. 

Advertisers use subliminal techniques to influence the second and third level of consciousness. They target the consumer's fears and desires, manipulating them in ways never thought possible. On the other hand, advertisers present to the consumer on the conscious level a safe, neutral, naturally appealing ad to pacify the consumer's resistance to subliminal advertising. While glancing through an ad, the average consumer block-reads paragraphs and barely notices an ad that they have seem many times. This is prime time in subliminal reception because the conscious mind is uninterested in the potentially offensive subliminal material. Key writes: 

To be effective, propaganda must constantly short circuit all thought and decisions. It must operate on the individual at the level of the unconsciousness. Critical judgment disappears altogether.