Humans receive information with sense organs, including their ears, nose, and eyes. These organs are part of larger sensory systems that receive information and send information to the brain. In visual perception, psychologists attempt to figure out how the information transmitted from the sense organs creates the foundation of perception. In other words, psychologists attempt to explain why, for example, you perceive a chair when the light hits your eye or why, when a sound wave comes to you, you perceive that sound in a certain way. Psychologists still disagree on the extent to which perception relies upon the information found in the stimulus. The two main theories to explain how we process information are top-down processing and bottom-up processing, both of which have ardent backers in the psychological community.

TOP-DOWN PROCESSING

In 1970, psychologist Richard Gregory claimed that perception was constructive, and that when a person looks at something, they begin to perceptually hypothesize about it based on prior knowledge—and these hypotheses are, for the most part, always correct. Top-down processing is based on pattern recognition and using contextual information. For example, if you are trying to read someone’s poor handwriting, it will be harder to understand a single word than it will be to understand a complete sentence, because the meaning of the other words will help you understand by providing context.

Gregory estimated that around 90 percent of information that reaches the eye is lost by the time it gets to the brain. The brain then uses past experiences to construct a perception of reality. Perception involves a large degree of hypothesis testing, so that the information presented by the sense organs can be logical. As sensory receptors get information from the environment, this information is then combined with information on the world that has been previously stored from past experiences.

The Necker Cube

The Necker cube is used to justify and support the hypothesis of top- down processing by showing that incorrect hypotheses will result in errors of perception, like visual illusions.

If you stare at the crosses on the cube, you will notice that its orientation can seemingly ip. This single physical pattern is unstable and actually creates two perceptions.

Top-down adherents claim that the reason for the two perceptions is that the brain has developed two hypotheses that are both equally plausible based on the sensory input and on previous experiences, and it cannot decide between the two.

BOTTOM-UP PROCESSING

Not all psychologists believe that top-down processing is the correct interpretation of visual stimuli. Psychologist James Gibson disagrees with the claims of hypothesis testing, and claims instead that perception is more direct. Gibson states that sense can be made from the world in a very direct way, because there is enough information in our environment. In Gibson’s bottom-up processing, there is not any interpretation or processing of the information received, because this information is detailed enough. To support this argument, one can think about the following scenario: you are sitting on a fast moving train, and as you travel, objects closer to you pass by at a faster rate than objects that are farther away. The distance of faraway objects can be understood by their relative speed. In bottom-up processing (or data-drive processing), perception starts with the stimulus itself and is analyzed in a single direction—a simple breakdown of raw sensory information to increasingly more complex analyses.

Visualization from the Rear of a Train

After working with pilots on the subject of depth perception during World War II, Gibson came to the conclusion that perception of surfaces had more importance than perception of either depth or space, because surfaces have features that allow objects to be distinguished from one another. Gibson also claimed that part of perception was understanding the function of an object—for example, whether the object can be sat on, thrown, or carried.

While working in aviation, Gibson discovered something that he referred to as “optic ow patterns.”

As a pilot approaches a landing strip, the point that the pilot is moving towards appears still while the surrounding visual environment seems to actually move away from the point. Gibson claimed that optic ow patterns could give pilots unmistakable information when it came to their speed, direction, and altitude. By using the concept of optic ow patterns, Gibson was able to make a more complete, three-part description of his theory of bottom-up processing.

The Optic Array Landing Guide

Optic Flow Patterns

• If there are no changes or ow in the optic array, the perceiver is static. If there are changes or ow, then the perceiver is moving.
• The flow either comes from a specic point or moves to a specic point. The perceiver can tell which direction they are moving based on the center of the movement; if ow is moving towards the specic point, then the perceiver is moving farther away from it, but if the ow is coming out from the specic point, then the perceiver is moving towards it.

Invariants

Every time we move our eyes, head, or walk around, things start to shift in and out of our viewing eld. For this reason, it is rare that we see a stagnant view of objects or scenes.

• As you approach an object, the texture will expand, and as you move farther away from an object, the texture will contract.
• Because the ow of texture occurs the same way when moving around, it is known as invariant. This provides information about our environment and is an essential cue to showing depth.

• Texture and linear perspective are two good examples of invariants.

Affordances

Affordances are environmental cues that support perception and provide meaning. Gibson didn’t believe that long-term memory provided meanings, but instead thought an object’s potential use was directly perceivable. For example, a chair provides for the chance to sit and a ladder provides for the chance to climb up or down. Important affordances include:

• Optical array: The patterns of light from the environment that reach the eye.
• Relative brightness: Objects that feature clearer and brighter images are perceived as being closer.
• Relative size: As an object moves away, the image seen by the eye appears smaller, and objects that have smaller images are seen as being farther away.
• Height in the visual field: When an object is farther away, this means that it is usually higher in the visual field.
• Texture gradient: When an object moves away, the grain of texture will become smaller.
• Superimposition: When an image of one object is blocking another object’s image from being seen, this means the first object is viewed as being closer than the second object.

Neither Gregory’s nor Gibson’s theories are able to accurately describe all of the perception, and there have been additional theories put forth that claim top-down processes and bottom-up processes interact with one another to create the best interpretation. Regardless of the final solution, both interpretations of perception have paved the way for psychologists’ consideration of this difficult issue.