Size Constancy

When we see the same object up close and far away we perceive that the object that's farther away is smaller even though in reality they're the same size. This is called size constancy which  is when we perceive objects as having a constant size even when our distance from them varies. One example is in the picture below. The shoe up front seems larger than the one further back but based on our knowledge we already know that both shoes are the same size, our eyes are just perceiving them as different.

Brightness Constancy

Also called Lightness Constancy its when we perceive an object as having a constant lightness even while its illumination varies. This depends on the relative luminescence or the amount of light an object reflects relative to its surroundings. One example would be a piece of paper under a bright light verses the same paper under a dimmer light. Our eyes perceive the paper as being lighter with the bright light than in the dimmer light but based on our knowledge we know the white paper is always white no matter how dark or light it is.

Shape Constancy

When an objects shape changes depending on the angle we view it at even though the actual size cannot change is called shape constancy. Its when we perceive the form of familiar objects as constant even while out retinal images of them change. For example the CD below looks thin in the top left picture, but then in the one next to that the CD looks wider. Finally in the bottom picture the full surface o the CD is shown and it seems to have a different shape compared to the other two when really it doesn't; its just the angle of the camera that distorts our vision of seeing the whole CD.

One of the binocular cues is convergence.  This is a neuromuscular cue which causes one's eyes to turn inward when focusing on a closer object.  This allows the brain to know which object to focus on.  In the first picture, the eyes turn inward more because the pencil being looked at is held at a close distance.  In the second picture, the eyes are farther apart as they focus on the pencil, which is at an arm's length.

The fifth rule of perception  is figure-ground perception.  This is when one distinguishes a certain object (the figure) from other objects (the ground or background).  This rule can be seen in the pictures below.  In the first picture, the book page cannot be read because the focus is on the ground (the stool) instead of on the figure (the book page). In the second picture, the book page is clear, and the stool it sits on is blurry.  This is because the focus is on the figure and not on the ground, as opposed to the first picture, where the opposite is true.

The fourth rule of perceptual organization is proximity. This is when our mind groups nearby figures together.  For example, in the picture below, one would likely see one group of two purple stripes and two groups of three purple stripes instead of eight individual purple stripes.

Real-Life Motion Perception

Here's an example of our minds perceiving motion when there actually isn't any. The images are individual images drawn on different pieces of paper, but when shown rapidly, they give the illusion of motion (in this case, the video of a very catchy K-pop song).

*Taken from YouTube*