SENSATION AND PERCEPTION
6.1 Distinguish between sensation and perception
In this Chapter, we will discuss sensation and perceptions. We will distinguish between these two concepts then give a description of how sensation can be measure and some factors which influence human perception.
Distinction between Perception and Sensation
Perception is the ability to understand the stimulation that comes to the nervous system by way of the sense organs. It is a cognitive process that entails analysing of information, organizing of information and reasoning (in short, what we do with information).
The perceptual process begins with sensation. Sensation is the study of how the various receptor cells in the body translate physical energy into neural messages and how these messages reach the central nervous system and the experiences that result. Sensation therefore is raw sensory data for example what we see, hear, taste, etc while perception is the interpretation of theses data by the brain.
The sense organs receive information from the environment making us consciously aware of the surrounding world through vision, hearing, taste, smell and touch. How these data re received depends on the functioning of the sense organs and the physical condition of the body in transmitting the information to the central nervous system.
Sensation and the Sensory System
- The basic element in the nervous system is the nerve cell called the neuron. Neurons are found in the sensory tissues along nerve pathways, in the spinal column and in the brain itself.
- The receptor cells in the sensory tissue receive information from the environment. There are three types of receptor cells:
- Those that collect information outside the organisms body
- Those that collect information from surfaces within the body for example gut and blood vessel walls
- Those that collect information from within tissues for example muscles. These receptor cells record pressure and tension
- Information received by these receptors is converted into neural energy which is electrochemical in nature. The information is sent along sensory neurons to the spinal cord and to the brain at a speed of 200Mph. From the brain messages travel through nerves to the muscles or glands and this constitutes sensation that is, one becomes aware of what is sensed.
6.2 Describe how we can measure sensation
Measurement of Sensation
1. Absolute threshold in sensation
This is the weakest stimulus that any sensory system can detect; it is the smallest amount of physical energy that will produce a sensation. Our senses respond to quite low levels of stimulation for example out vision – we can see a candle thirty miles away on a clear, dark night or we can smell one drop of perfume in a three roomed house.
Dogs have a better sense of hearing and smell while hawks have a keener sense of sight. Some fish have taste buds all over their bodies. Human beings can only see a fraction of the light waves surrounding them. They cannot see ultra violet rays or infra red rays.
2. Differential threshold
Differential threshold is the amount of change in a physical stimulus necessary to produce a just noticeable difference in sensation. Here we are talking about the smallest change in stimulation that a person can detect. An example is a good cook tastes a dish, then adds salt to it, then tastes it again to measure the change. Our ability to detect differences in stimulus intensity depends on the magnitude of the initial stimulus, we easily detect even small changes in weak stimulus, but we require much larger changes before we notice differences in strong stimuli for example small adjustments in soft music will be noticed while it takes longer to notice small adjustments in loud music.
Basic Mechanism of Perception – The Visual System
The visual sense is the most important in terms of human perception. About 80% of the information taken in from the environment comes through the organs of sight. Light is an electromagnetic energy force that travels through space at approximately 186,000 miles per second from sources like the sun, candles or electric bulbs. This energy travels in waves which hit surfaces at different intervals and with different force. The waves of light travel in varying lengths and intensities. All the wavelengths of light appear as a colourless white. When they strike a surface they scatter and each appears as a different colour or hue. Human beings are only able to utilize a small portion of the light waves that is 400 to 700 nanometres called the visible spectrum. The human eye cannot see ultraviolet or infrared rays.
Light is received through the pupil of the eye. It falls on the photosensitive surface called the retina. The retina contains 127 million light sensitive receptor cells. Their job is to convert light energy into electrochemical energy. These cells contain photo-pigments that react chemically to light. There are two types of cells that is, cones and rods. There are seven million cones in each eye.
Principles of Perceptual Organisation
These principles were developed by a group of psychologists called Gestaltists in an effort to try and explain how humans impose organisation on stimuli that they attempt to perceive for instance the occurrence of illustrations and false impressions is due to such imposed organisations.
1. Law of proximity
Several elements are seen as a coherent object by virtue of being spatially close to one another for example in the following illustration, the dots are seen to form a rectangle because they are close together
. . .
. . .
. . .
. . .
2. Law of similarity
An image is organized by similarity among its elements for example in the following illustration, there is a tendency to see a row of X’s and a row of O’s.
X O X
X O X
X O X
3. Law of continuation
The law states that the perceiver will continue contours whenever the elements of the pattern establish an implied direction for example in the following illustration there is a tendency to view the three lines as continuing in one direction
_________ ___________ _____________
4. Law of closure
This law states that humans tend to enclose a space by completing a contour and ignoring gaps in the figure. For example in the following illustration, one sees a complete circle and square but does not easily notice the gaps
5. Law of prägnanz (good figure)
A stimulus will be organised into as good a figure as possible. The term “good” in this sense implies symmetrical, simple and regular. For example in the following illustration, we tend to perceive the figure below as two overlapping triangles instead of two small triangles and two irregular quadrilaterals because we tend to interpret a stimulus in the simplest terms.
The principles of perceptual organisation make it possible for our eyes to play tricks on us. There are several illusions:
1. Műller-Lyer Illusions
Two lines are the same length, but the line on the left, with its reversed arrowheads looks longer.
2. The ponzo illusion
This can easily be seen when one stands on a railway line. The bars that are farther away look shorter and smaller than the rails that one is standing on. Although all the bars on a railway line are the same size, those that are far away look smaller.
3. The moon illusion
The moon looks very much larger when it is on the horizon than when it is viewed at the zenith that is, at the highest point in the sky. Clearly the size of the retinal image does not change as the moon travels through the sky, yet in phenomenological terms the moon is perceived as being much larger than at the zenith.
Extra Sensory Perception (ESP)
Normally when we speak of perception we refer to sensory perception that is perception that takes place through the senses. It has however been suggested that there may be perceptions that do not require any sense organ stimulation. This is called extra-sensory perception. Several classifications of ESP exist. These are:
This means transference of thought from one person to the other. It is when an individual claims to be able to tell what another person is thinking about for example being able to tell what the person seated next to you in the bus is thinking about.
This is perceptions of objects or events that are not influencing the senses for example reading a card that is in a sealed envelope. No one knows what is in the envelope so in this case it is not another person’s mind that is being read.
With precognition, a person perceives an event that has not yet taken place that is, the person predicts the future.
This has to do with the influence of a mental operation over a physical body for example telling a book to open itself.
This is the ability to transport materials, objects or people by means of mental processes
Note: ESP has created a lot of controversy because these issues cannot be replicated and cannot be systematically investigated therefore cannot be measured. Many psychologists and scientists therefore do not believe in ESP.
6.3 Discuss the factors which influence human perception
Factors which influence Human Perception
1. Halo Effect
This is the tendency of letting your impressions or judgement of an individual be influenced by ones general impression of him or her for example a good student can easily get extra marks in an assignment.
2. Socio-cultural factors
We tend to judge others by our standards for example perception of beauty varies from one part of the world to another. In European societies, extremely thin women are seen as beautiful while in West African societies, it is very fat women who are viewed as being very beautiful.
3. Context or frame of reference
This is a framework which serves as a reference against which the properties of a particular object are perceived. It can determine or distort out perception. For example, when one sees the following two lines, one can easily assume that the second figure in the first line is the letter “B” while the second figure in the second sentence is seen as the number “13”.
12 B 14 15
A B C D
The predisposition to act in a certain way is tied up with past experience for example if someone treated us badly, the next time we see them, we might approach them with caution.
- Individual personal adjustments, needs and wants
There is a relationship between an individuals needs, wants and his perception for example some parents are poor in perceiving their children’s faults and a person in love perceives his or her lover differently.
- State of health
When an individual is sick, he or she may see things differently for example, if an individual is sick and has to do an exam on that day, he might find the exam more difficult than he would if he did the exam when he is not sick.
- Mental state
An individual’s mental state also affects perception for example when one is drunk, one may perceive a prostitute in a bar as a very beautiful woman and will want to go home with her but when he is sober, he will not want anything to do with the prostitute.
In this chapter we have described sensation and perception and given a distinction between these two concepts. We have also discussed some of the principles of perceptual organisation and talked about the factors which influence human perception.
6.9 Self Assessment Questions
- Describe two factors that influence human perception
- Using relevant examples describe the various thresholds in sensation
- Write an essay on how perception influences the way individuals react to situations
6.10 Further Reading
Morris, C. (1980). Psychology and Introduction. New Jersey: Prentice Hall.
Myers, D. G. (1990). Exploring Psychology. New York: Worth Publishers Inc.
Silverman, R. E. (1982). Psychology. Englewood, New Jersey Cliffs: Prentice Hall Inc.