Another kind of change is novelty, or newness. As we drive down the same old road every day on our way to school, we see the same old things. However, if one day a new sign has been posted or a traffic light installed we notice it. Recently, my-three-year old noticed that the sign announcing the county fair was no longer there. It had a cow on it, so it had been a favorite. I had not noticed its disappearance, but he had. The sign is now back up, but again he noticed its reappearance before I did.
There is an optimal amount of stimulus complexity for perception. That means that we soon learn to ignore simple stimuli, and we may never bother to perceive extremely complex stimuli. But, in between those two extremes we each find a level of complexity that engages us perceptually. For example, infants soon tire of looking at colors. They will look at faces for much longer, but they will "tune out" a complex collection of stimuli like a light and sound show.
Advertisers have long known the perceptual properties of repeated stimulation. "Buy soap, buy soap, buy soap, buy soap.....", the radio drones on. But after awhile we find it hard to forget that ad.
This is an example of intensity.
You will be more likely to perceive that sentence when it is printed in large, bold type. The same would be true of loud sounds, strong odors, and other intense sensory experiences.
This is an example of contrast.
Notice that the sentence above is printed in italic, is right justified, and is smaller than what you have been reading all along. You notice it because it, too, is an example of change from what you have been used to.
Movement is a powerful perceptual cue. Preying mantis females will attack and eat anything smaller than they that moves. Most preying mantis males die during copulation because of that perceptual tendency. Some males do live to copulate more than once because they do not move when the female looks their way. Or, think of when you are studying late at night and out of the corner of your eye you see a cockroach scurry by. That roach might have been standing there a long while before it moved and you perceived it.