Perceptual Constancies: Part 3 -- Shape Constancy

Shape Constancy is the tendency to perceive the shape of a rigid object as constant despite differences in the viewing angle. For example, when opening a door we know the door remains the same shape even though from different viewing angles the shape looks different. Our brains learn this from knowing that the shape of an object usually won’t change and that the objects shape will remain constant even when viewed from a different angle.

Perceptual Constancies: Part 2 -- Brightness Constancy

Brightness Constancy is the tendency for a visual object to be perceived as having the same brightness under widely different conditions of illumination. Brightness Constancy is based largely on prior knowledge and past experiences. The less experience had with an object, the less the effects of Brightness Constancy. A good example of Brightness Constancy is snow which can appear white under the light of the moon or under the light of the sun with provides much more brightness. It is useful in the way that it allows us to know the color of an object even under low levels of light.

Perceptual Organization: Part 1 -- Size Constancy

Perceptual Constancies: The tendency of animals and humans to see familiar objects as having standard shape, size, color, or location regardless of changes in the angle of perspective, distance, or lighting.

Size constancy is the tendency to perceive the veridical size of a familiar object despite differences in their distance.  This means that within a certain range, people’s perception of one particular objects’ size will not change, regardless of changes in distance. This is useful in that it will allow a person or animal to see objects in their actual size unless they are very far away. Some examples of size constancy are the Muller-Lyer illusion and Ponzo illusion. The image shown proves that are brain will make objects that are perceived to be farther away bigger so that they more accurately display their actual size. In the image both yellow lines are the same size.

Motion Perception

Motion Perception: Motion perception is the process of inferring the speed and direction of objects that move in a visual scene given some visual input.

Motion Perception is relatively difficult to explain and there is still more to be learned about it. In order to find the speed and direction of an object the human brain has to compare it to its surroundings. For example, if a ball is thrown in the middle of a field we know how fast the ball is going by assuming the surroundings (the field) is still and comparing their speeds. However, if the same ball is thrown in a bus moving ten miles per hour it may appear to be moving the same speed as in the field when in reality it is actually moving ten miles per hour faster since we assume our surroundings, the bus, is still when in fact it is moving ten miles per hour. Our brain also detects motion by taking very quick snap shots and putting them together to form what appears to be a continuously moving scene. Between these snap shots or when we blink are mind fills in the information it thinks we are missing. Examples of this continuous motion illusion can be found in the film of old movies.

Monocular Cues: Part 2 -- Linear Perception

Linear perception is the monocular cue provided by the convergence of lines toward a single point of the horizon. Looking down a set of railroad tracks or down a long strait road is a good example. We know that the tracks do not meet (they are parallel the entire time) but they appear to come together at a single point.

Monocular Cues: Part 1 -- Relative Size

Monocular Cues:  Unlike Binocular cues that work in three dimensions and work with both eyes, Monocular cues are in two dimensions and are a set of depth-cues that are available to us with just one eye. These cues provide us with solid depth-perception information.

The first example of Monocular Cues is Relative Size. Over time, our brains have learned that objects change size very slowly if at all. In other words, people don’t shrink to half their size, or double their size in an eye blink. It is because of this that we know that a person who is shrinking isn’t actually growing smaller but is moving farther away. When the image of an object gets larger on the retina, we interpret that it is getting closer. Conversely, when the image on the retina gets smaller, we interpret that as the object becoming farther away. A good example of Relative Size is knowing that from the top of a building people below are actually normal sized and far away rather than simply very small.

Depth Cues: Part 1-- Binocular Cues

Depth perception: "the ability to judge the distance of objects and the spatial relationship of objects at different distances" (merriam-webster.com).

Humans judge depth perception in two main ways:  using monocular cues and using binocular cues.  Monocular cues are those that only need one eye to work.  Binocular cues, on the other hand, are cues that need both eyes to work.  One such binocular cue is demonstrated above.  As the woman brings her finger closer to her nose, her eyes begin to move inward toward the nose, eventually becoming completely cross-eyed.  This demonstrates the binocular cue of convergence.  Convergence states that as an object gets closer to our face, our eyes move toward each other to maintain focus on the object.  The more our eyes are turned inward, the closer the object.  In this case, the finger was very close to the face, causing the eyes to turn as far inward as they could to accommodate.  The next post for Depth Cues is a more in-depth look into various Monocular Cues.  Stay tuned!