Perception by Dr Anmol Arora

Perception is the process by which organisms interpret and organize sensation to produce a meaningful experience of the world.

The word perception comes from the Latin perception, percepio, , meaning “receiving, collecting, action of taking possession, apprehension with the mind or senses.”

In order to receive information from the environment we are equipped with sense organs eg eye, ear, nose. Each sense organ is part of a sensory system which receives sensory inputs and transmits sensory information to the brain.

A particular problem for psychologists is to explain the process by which the physical energy received by sense organs forms the basis of perceptual experience. Sensory inputs are somehow converted into perceptions of desks and computers, flowers and buildings, cars and planes; into sights, sounds, smells, taste and touch experiences.

A major theoretical issue on which psychologists are divided is the extent to which perception relies directly on the information present in the stimulus. Some argue that perceptual processes are not direct, but depend on the perceiver’s expectations and previous knowledge as well as the information available in the stimulus itself. This controversy is discussed with respect to Gibson (1966) who has proposed a direct theory of perception which is a ‘bottom-up‘ theory, and Gregory (1970) who has proposed a constructivist (indirect) theory of perception which is a ‘topdown‘ theory.

Psychologists distinguish between two types of processes in perception:

1. Bottom-up processing and
2. Top-down processing.

Bottom-up processing is also known as data-driven processing, because perception begins with the stimulus itself. Processing is carried out in one direction from the retina to the visual cortex, with each successive stage in the visual pathway carrying out ever more complex analysis of the input.

Top-down processing refers to the use of contextual information in pattern recognition. For example, understanding difficult handwriting is easier when reading complete sentences than when reading single and isolated words. This is because the meaning of the surrounding words provide a context to aid understanding.

Sensation usually refers to the immediate, relatively unprocessed result of stimulation of sensory receptors in the eyes, ears, nose, tongue, or skin. Perception, on the other hand, better describes one’s ultimate experience of the world and typically involves further processing of sensory input. In practice, sensation and perception are virtually impossible to separate, because they are part of one continuous process.

Thus, perception in humans describes the process whereby sensory stimulation is translated into organized experience. That experience, or percept, is the joint product of the stimulation and of the process itself. Relations found between various types of stimulation (e.g., light waves and sound waves) and their associated percepts suggest inferences that can be made about the properties of the perceptual process; theories of perceiving then can be developed on the basis of these inferences. Because the perceptual process is not itself public or directly observable (except to the perceiver himself, whose percepts are given directly in experience), the validity of perceptual theories can be checked only indirectly.

Historically, systematic thought about perceiving was the province of philosophy. Philosophical interest in perception stems largely from questions about the sources and validity of what is called human knowledge (epistemology). Epistemologists ask whether a real, physical world exists independently of human experience and, if so, how its properties can be learned and how the truth or accuracy of that experience can be determined. They also ask whether there are innate ideas or whether all experience originates through contact with the physical world, mediated by the sense organs.

As a scientific enterprise, however, the investigation of perception has especially developed as part of the larger discipline of psychology. For the most part, psychology bypasses the questions about perceiving raised by philosophy in favour of problems that can be handled by its special methods. The remnants of such philosophical questions, however, do remain; researchers are still concerned, for example, with the relative contributions of innate and learned factors to the perceptual process.

Factors affecting perception

Various factors influence what and how we perceive. Our perceptions are influenced by the ways our bodies are structured to receive and process stimuli from the environment. Our perceptions also reflect our emotions, needs, expectations, and learning.

Receptors. Each sensory system, such as vision, hearing, or touch, has its own specialized body parts. These parts are called receptors, and they change energies from the environment into nervous impulses. The human eye, for example, has two major kinds of receptors in the retina (the light-sensitive part of the eye). These receptors are called rods and cones. The rods respond to the intensity of light, but not to different frequencies of light (different colours). The cones do respond to different frequencies of light, and are called colour receptors. The rods allow us to see in dim light, and the cones enable us to see colours and sharp detail in bright light. Thus, the particular ways that receptors are structured and function help determine the perceptual effects related to them.

The brain. Certain physical and functional features of the brain also determine some aspects of perception. The part of the brain that serves vision has different kinds of cells that respond only under certain conditions of stimulation. Some of these cells respond only when a light goes off. Others respond when a light comes on, but they stop responding if the light stays on. Such cells also are arranged in special ways in the brain, and this fact is related to how we perceive. For example, some cells are arranged in columns or in clusters. Such arrangements are related to how we perceive edges and forms. Experiments suggest that some cells in the brain allow us to perceive movement. Thus, the structure of the brain is an important element in perception.

Learning, emotion, and motivation.

Much evidence points to the conclusion that early experience, learning, emotion, and motivation are important in defining what and how we perceive. Part of this accumulating evidence comes from experiments that compare how people in different cultures perceive things. The perception of such things as form, colour, pain, and touch may differ from culture to culture, depending on habits and customs, and training of children.

Some illusions are related to learning and past experience. An illusion is not a false perception, as many people believe, but one that is inconsistent with another perception. Since perception does not literally reveal the environment, no sensory system is closer to some absolute truth than any other. We tend to check visual illusions against touch, but touch can involve illusory effects, too..

Emotions and motivation can have an important effect on perception. Sometimes a severe emotional disturbance can prevent perception completely, as when emotional shock causes individuals to lose their hearing temporarily. We are more likely to perceive those aspects of our environment that are related to our motives. For example, motivation can affect the perceived characteristics of objects. To hungry people, food may appear larger or more colourful than usual.

Understanding perception

Types of perception.

Perception has three levels of complexity: (1) detection, (2) recognition, and (3) discrimination.

Detection refers to whether people can sense that they are being stimulated by some form of energy. For example, a light may be so dim they can barely detect its presence.

Recognition means being able to identify as well as detect a particular pattern of stimulation.

Discrimination means being able to perceive one pattern of stimulation as different from another. For example, a person may hear slight differences between two similar musical tones.

The field of study that deals with levels of perception is called psychophysics. Experimental psychologists investigate the relationships between the physical properties of stimulus patterns and the perceived effects of the stimuli. For example, they may study the relationship between sound frequency and the perceived pitch of sound.

1. Amodal perception
2. Color perception
3. Depth perception
4. Form perception
5. Haptic perception
6. Speech perception
7. Psychophysics
8. Sensory perception
9. Visual perception
10. Auditory perception
11. Speech perception
12. Smell perception
13. Taste perception
14. Time perception
15. Movement and action

Amodal perception is the term used to describe the full perception of a physical structure when it is only partially perceived. For example, a table will be perceived as a complete volumetric structure even if only part of it is visible; the internal volumes and hidden rear surfaces are perceived despite the fact that only the near surfaces are exposed to view, and the world around us is perceived as a surrounding void, even though only part of it is in view at any time

Depth perception is the visual ability to perceive the world in three dimensions. Although any animal capable of moving around its environment must be able to sense the distance of objects in that environment, the term perception is reserved for humans, who are the only beings that can tell each other about their experiences of distances.

Haptic perception active touch perception is  known as human haptic perception

Form perception is one of the most basic visual discriminations that a child has to make. Whether it be the differentiation of the shape of a circle from a square, or the letter B from P, the ability to perceive the shapes of objects and pictures is an important skill for the developing child to acquire.

Gestalt Principles of Grouping

The German word “Gestalt” roughly translates to “whole” or “form,” and the Gestalt psychologist’s sincerely believed that the whole is greater than the sum of its parts.  In order to interpret what we receive through our senses, they theorized that we attempt to organize this information into certain groups.  This allows us to interpret the information completely without unneeded repetition.  For example, when you see one dot, you perceive it as such, but when you see five dots together, you group them together by saying a “row of dots.”  Without this tendency to group our perceptions, that same row would be seen as “dot, dot, dot, dot, dot,” taking both longer to process and reducing our perceptive ability

Gestalt psychology was founded by German thinkers Max Wertheimer, Wolfgang Kohler, and Kurt Koffka and focused on how people interpret the world. The Gestalt perspective formed partially as a response to the structuralism of Wilhelm Wundt, who focused on breaking down mental events and experiences to the smallest elements. Max Wertheimer noted that rapid sequences of perceptual events, such as rows of flashing lights, create the illusion of motion even when there is none. This is known as the phi phenomenon. Motion pictures are based upon this principle, with a series of still images appearing in rapid succession to form a seamless visualexperience.

As according to Gestalt psychology, the whole is different than the sum of its parts. Based upon this belief, Gestalt psychologists developed a set of principles to explain perceptual organization, or how smaller objects are grouped to form larger ones. These principles are often referred to as the “laws of perceptual organization.”

1. Law of Proximity

Elements that are closer together will be perceived as a coherent object.

On the left, there appears to be three horizontal rows, while on the right, the grouping appears to be columns.

2. Law of Similarity

Elements that look similar will be perceived as part of the same form.

There seems to be a triangle in the square.

1. Law of Good Continuation

Humans tend to continue contours whenever the elements of the pattern establish an implied direction.

People tend to draw a good continuous line.

4. Law of Closure

Humans tend to enclose a space by completing a contour and ignoring gaps in the figure.

5. Law of Prägnanz

A stimulus will be organized into as good a figure as possible. Here, good means symmetrical, simple, and regular.

The above figure appears to the eye as a square overlapping triangle, not a combination of several complicated shapes.

6. Law of Figure/Ground

A stimulus will be perceived as separate from it’s ground. .

The above figure appears to the eye as a square inside a circle, or as a donut shaped circle with a square hole.

Figure/ground reversals create a delightful “surprise” in the viewer’s eye. (Many of the best logos designed will use figure/ground reversal to their advantage.)

Maintaining Perceptual Constancy

Imagine if every time an object changed we had to completely reprocess it.  The next time you walk toward a building, you would have to re-evaluate the size of the building with each step, because we all know as we get closer, everything gets bigger.  The building which once stood only several inches is now somehow more than 50 feet tall.

Luckily, this doesn’t happen.  Due to our ability to maintain constancy in our perceptions, we see that building as the same height no matter what distance it is.

Perceptual constancy refers to our ability to see things differently without having to reinterpret the object’s properties.  There are typically three constancies discussed, including size, shape, brightness.

Size constancy refers to our ability to see objects as maintaining the same size even when our distance from them makes things appear larger or smaller.  This holds true for all of our senses.  As we walk away from our radio, the song appears to get softer.  We understand, and perceive it as being just as loud as before.  The difference being our distance from what we are sensing.

Everybody has seen a plate shaped in the form of a circle.  When we see that same plate from an angle, however, it looks more like an ellipse.  Shape constancy allows us to perceive that plate as still being a circle even though the angle from which we view it appears to distort the shape.

Brightness constancy refers to our ability to recognize that color remains the same regardless of how it looks under different levels of light.  That deep blue shirt you wore to the beach suddenly looks black when you walk indoors.  Without color constancy, we would be constantly re-interpreting color and would be amazed at the miraculous conversion our clothes undertake.

Perceiving Distance

We determine distance using two different cues: monocular and binocular.  Monocular cues are those cues which can be seen using only one eye.  They include size; texture, overlap, shading, height, and clarity.

Size refers to the fact that larger images are perceived as closer to us, especially if the two images are of the same object.   The texture of objects tend to become smoother as the object gets farther away, suggesting that more detailed textured objects are closer.  Due to overlap, those objects covering part of another object is perceived as closer.  The shading or shadows of objects can give a clue to their distance, allowing closer objects to cast longer shadows which will overlap objects which are farther away.  Objects which are closer to the bottom of our visual field are seen as closer to us due to our perception of the horizon, where higher (height) means farther away.  Similar to texture, objects tend to get blurry as they get farther away, therefore, clearer or more crisp images tend to be perceived as closer (clarity).

Binocular cues refer to those depth cues in which both eyes are needed to perceive.  There are two important binocular cues; convergence and retinal disparity.  Convergence refers to the fact that the closer an object, the more inward our eyes need to turn in order to focus.  The farther our eyes converge, the closer an object appears to be.  Since our eyes see two images which are then sent to our brains for interpretation, the distance between these two images, or their retinal disparity, provides another cue regarding the distance of the object.