Perception without awareness occurs when the brain receives information from a particular stimulus. The brain does not remember actually seeing or hearing the stimulus but (of course) it is there nonetheless. After time passes, the stimulus will have affected the person through their behavior or thoughts, even though they don't realize this has happened.

But how does one know when this has occurred? When a person's thoughts or behaviors have been affected by the direct stimulus is how we know that perception without awareness has occurred. Several things have to take place for anyone to be absolutely certain that this has taken place.

It can happen just by simultaneously thinking the same thought as another person. These thoughts are seemingly unrelated to anything in your direct stimulus path. You might both suddenly start to think of the same song, unaware that you had both heard it only moments before. You had simply been too preoccupied with the conscious brain to realize that the music had been playing.

A new neighbor may have moved into the neighborhood and you just know that they belong to the police force. Even though you've not met them. When you finally meet them, you find out that they are a plain clothes detective on the police force. Do you have a sixth sense?

The brain did hear the song and started to playback what it had heard. Unfortunately, this does happen a lot. It is almost impossible to know how much the brain picks up even when it is unfocused. It is often why people go under hypnosis when they have been a witness to a crime.

This is different than sitting on your porch with some friends and trying to figure out what the new neighbor does for a living. By taking part in this activity, you are consciously looking for telltale signs of their occupation. Not only is your brain aware at this point, is it actively seeking stimulus. Perception without awareness can give us all kinds of interesting information.