TOPIC: SENSATION AND PERCEPTION
As man lives, vast information are continuously accepted by the senses or sense organs. Every second of life, the senses are functioning to connect the internal or physiological body to the external world or vice-versa. Through man’s development in life (from birth to death), the senses are continuously affected by one stimulus after another.
The process of accepting the stimulus by the sense is called sensation. The giving of interpretation or meaning to the stimulus by the brain to respond appropriately is referred to as perception. Stimulus is any for of energy that can cause awareness or change to the consciousness (light waves, sound waves, temperature, chemical state – liquid, solid, gaseous, etc.) these stimuli are then modified and accepted by the accessory structures (eyes, ears, nose, skin, tongue). From the accessory structures, transduction occurs at the receptors. Receptors are specialized cells responsible for detecting specific type of energy as a result of transduction. Transduction is the process of changing the stimulus sense into energy for neural activity. The energy transduced at the receptor is received by the sensory nerve on to the thalamus, then to the brain for the corresponding response.
19th century German psychologist Gustav Fechner used the term absolute threshold to refer to the weakest level of a stimulus that is necessary to produce a sensation. Psychophysicists look for the absolute thresholds of the senses by exposing individuals to progressively stronger stimuli until they find the minimum stimuli that the person can detect 50% of the time. These absolute thresholds are not all that absolute, however. Some people are more sensitive than others, and even the same person might have a slightly different response at different times. Nevertheless, under ideal conditions, our ability to detect stimuli is quite sensitive.
Examples: a. Vision: a candle flame viewed from about 30 miles on a clear, dark night. b. Hearing: a watch ticking from about 20 feet away in a quiet room. c. Taste: 1 teaspoon of sugar dissolved in 2 gallons of water d. Smell: about one drop of perfume diffused throughout a small house. e. Touch: the pressure of the wing of a fly falling on a cheek from a distance of about 0.4 inch
How much of a difference in intensity between two lights is required before you will detect one as being brighter than the other? The minimum difference in intensity required between two sources of energy so that they will be perceived as being different is called difference threshold.
Sensory adaptation. An important characteristic of the sense receptors is their ability to make adaptations to changes. This is the ability to adjust to a particular stimulus. This means that a sense receptor may no longer be sensitive to certain stimulus as it persists for a certain period of time. This is a characteristic common to vision, smell and temperature. (ex. Movie house – adjustment of your eye to the light/darkness; living in a market – odor in your environment)
Light enters first by passing through the cornea (the transparent protective covering curved tissue in front of the eye). Behind the cornea, the light continues to the front chamber which contains watery liquid (aqueous humor – to provide nutrients and keep the cornea moist). Then the light enters through the pupil
(a small hole at the center of the black circle of the eyes). The pupil controls the amount of light by constricting (closing) on too much light and dilating (opening) under dark condition. The iris is the colored muscles of the eye responsible for reducing or enlarging the size of the pupil.
From the pupil, the light extends to the lens.
The lens is an elastic curved structure that bends
Light rays in order to focus a clear image to the retina. As the light reaches the retina, it crosses a clear fluid called the vitreous humor. The lens changes its shape upon focusing in near or far image in a process known as accommodation. The lens constricts on focusing near view and stretches on focusing far view. Light rays are bent by the lens to meet at a point to the retina. The image will be out of focus if the rays meet in front of the retina (nearsighted) or behind the retina (farsighted). The retina is an intricate network of cells containing neurons ganglion cells and photoreceptors. It is in the retina where visual transduction takes place. This is the conversion of light energy into neural activity so that the stimulus can be transmitted to the brain. Information is then sent to the brain through a bundle of nerve fibers that forms the optic nerve.
The wavelength of light determines its color or hue. The value of a color is its degree of brightness or darkness. The saturation refers to how intense a color appears to us. A fire-engine red is more saturated than a pale-pinkish red.
If you can discriminate among the colors of the visible spectrum, you have normal color vision and are labeled a trichromat. This means that you are sensitive to red-green, blue-yellow and light-dark. People who are totally color-blind are called monochromats. They are only sensitive to lightness and darkness. This is rare and fully color-blind individuals sees the world in a black-and-white movie. Partially color-blind people are called dichromats. This is a sex-linked trait that affects mostly males. they can discriminate only between two colors – red and green or blue and yellow – and the colors that are derived from mixing these colors.
Sound waves are collected by the skin-covered cartilage protruding on the side of the head known as pinna or auricle. From the pinna, sound waves enter the auditory meatus (opening) and pass through the external auditory canal. The auditory canal contains lining of tiny hairs and wax glands which lubricate and subsequently protect the inside of the ear by trapping dirt and insects. The sound waves extend down from the auditory canal and hit the tympanic membrane (eardrum), the start of the middle ear. The eardrum, causes the sound waves to vibrate to match the sound produced. The vibrated matched sound produced is conducted to the 3 smallest bones in the body named for their shape: the malleus (hammer), incus (anvil) and stapes (stirrup). The 3 suspended chained tiny bones convert the action of sound pressure into mechanical movements.
The sound waves goes to the fluid-filled coiled or spiral inner ear. The inner ear begins with the cochlea (Greek word “snail”), where transduction happens. The increased pressure relays sound energy to this fluid developing pressure waves in the basilar membrane within the cochlea. The basilar membrane is composed of hair cells (cilia) responsible for the release of neurotransmitters. The neurotransmitters are produced when the pressure causes the basilar membrane to move up and down. Hence, the current flow of fluid moves the cilia to release neurotransmitters on to the dendrites of the auditory nerve. The auditory nerve then carries the stimulus (information) to the opposite hemisphere of the cerebral cortex in the temporal lobe.
Touch and Pressure
Sensory receptors embedded in the skin fire when the surface of the skin is touched. There may be several kinds of receptors for touch, some that respond to constant pressure, some that respond to intermittent pressure, as in tapping the skin. Active touching means continually moving your hand along the surface of an object so that you continue to receive sensory input from the object. Ex. If you are trying to “get the feel of” a fabric or the texture of a friend’s hair, you must move your hand over it. Otherwise, the sensation quickly fade. Active touching receives information concerning pressure, temperature, texture, and feedback from the muscles involved in movements of our hands.
Different parts of the body are more sensitive to touch and pressure than others. Our fingertips, lips, noses, and cheeks are more sensitive than our shoulders, thighs, and calves. Why the difference in sensitivity? First, nerve endings re more densely packed in the fingertips and face than in other locations. Second, more sensory cortex is devoted to the perception of sensations in the fingertips and face.
The receptors for temperature are neurons located just beneath the skin. When skin temperature increases, the receptors for warmth fire. Decreases in skin temperature cause receptors for cold to fire.
Headaches, backaches, toothaches – these are only a few of the types of pain that most of us encounter from time to time. According to a national survey, 89% experience pain at least once a month. More than half (55%) of people aged 65 and above say they experience pain daily. People aged 65 and above are most likely to attribute pain to getting older. By contrast, people aged 18-34 are more likely to attribute pain to tension or stress, overwork or their lifestyle.
Pain results when neurons called nociceptors in the skin are stimulated. We can sense pain throughout most of the body, but pain is usually sharpest where nerve endings are densely packed, as in the fingers and face. Pain usually originates at the point of contact, as when you bang a knee. The pain message to the brain is initiated by the release of chemicals such as prostaglandins, bradykinin, and P (stands for pain). Prostaglandins facilitate transmission of the pain message to the brain and heighten circulation to the injured area, causing the redness and swelling that we call inflammation.
The gustatory sense (taste) and olfactory sense (smell) are referred to as chemical senses. They relate closely in reacting to chemical substances in different stimuli. The receptors for gestation are the taste buds. These receptor cells are connected to nerve fibers that bring taste signals or information to the brain. They have four basic tastes: sweet, sour, salty, and bitter. These tastes are situated in different areas and are somewhat independent. The cells’ taste die and generate new cells about every ten days. Also, as the individual ages, there is a decrease in the cells and small amount of cells are replaced. Most elderly people are delicate and selective when it comes to food: the reason why they go for expensive and classic cuisine or gourmet.
Odors of gaseous state are senses in the upper part of the nose. Molecules enter through the nostrils (opening) or from the back of the mouth (oral cavity) into the nasal cavity. Hence, olfaction is a dual sense; it can smell internally (oral cavity) and externally (nasal cavity). The nasal cavity contains the olfactory mucosa, a membrane providing moisture. The olfactory mucosa is lined with cilia (hairlike projections). The olfactory mucosa and cilia together trap molecules not needed and produce electrical signals. Electrical signals are sent to the receptors, the
“olfactory bulb”. From the olfactory bulb, signals are then sent and processed into the brain.
According to Henning, there are six basic smells that can be perceived or determined by the brain: fragrant, fruity, spicy, putrid (decomposition), resinous (smell of plants/woods) and burned.
KINESTHESIS AND THE VESTIBULAR SENSE
Kinesthesis is the sense that informs you about the positions and motion of the body. The receptor cells are in the nerve endings of the muscles, tendons, and joints. these receptor cells respond in sensing body movements depending on the direction and angle of movement. Thus, kinesthetic receptors give feedback on the need to regulate posture and body movements.
Vestibular sense tells you whether you are physically upright. It is also known for the sense of balance. Sensory organs located in the semicircular canals and elsewhere in the ears monitor your body’s motion and position in relation to gravity. They tell you whether you are falling and provide cues to whether your body is changing speed, such as when you are in an accelerating airplane or automobile.
Perception interprets meaningful experiences in totality. The meanings on how the brain organized previous and present knowledge or information are obtained. The sensation gathers the information, which is then absorbed in the brain in the form of perception. Perception is subjective in interpretation as brought about by experiences. A particular object can mean differently for varied individuals. One thinks it is positive, the others negative, to some nothing at all, or they are unaware of the stimulus.
GESTALT PRINCIPLES OF BASIC PERCEPTUAL ORGANIZATION
The gestaltists maintain that an individual tends to perceive things in an organized meaningful whole and the result is a unitary experience. To them, the stimuli that are perceived are not seen as separate elements but organized into coherent units. One sees a piano; he perceives it not only as a piece of musical instrument but as something from which he can derive pleasant aesthetic experiences.
They formulated principles as to how we perceive objects. The first of these was the organization of the perceptual field. According to them, objects are perceived easier when grouped into meaningful patterns. The simplest perception of a figure is that it has a certain shape or contour and that it stands out in a background. When there are several elements, they are easier perceived when grouped together as in a figure-ground group where the tendency of the perceiver is to see the figure, then the background, then the figure, and so on.
A second way of grouping stimuli is by grouping them into patterns since these have several parts. The stimulus elements are grouped on the basis of confi- gurational principles as suggested by the Gestaltists.
These are the principles of similarity, proximity, closure, and continuity.
According to this principle, stimuli of similar sizes, shapes, and even colors, tend to be grouped together.
Similarly, in a big group of school children, how can you tell from what school they come? You look at their uniforms and say that those wearing white blouses and dark blue skirts are from one school; those wearing white blouses but dark green blouses come from another. When in a depart- ment store, do you notice how easy it is to look for the items you need because similar objects have been grouped together? Proximity.
The tendency is for one to perceive stimuli near one another as belonging together. Suppose a basketball player was asked to dribble a ball twice for 3 consecutive times and you are asked to report how many times the ball was dribbled. You will likely report that the ball was dribbled two times in 3 successions instead of six times.
The perceiver tends to complete an incomplete figure.
For example, a child would report having seen one table in the room although he had seen only a part of the table.
Any line or movement tends to be perceived as continuing in the direction already started.
As you watch a television program, you notice the images of characters appearing on your screen changing from time to time. In spite of all the movements that they make, the characters are not perceived as distorted in shape, size, height, and even in color. They are essentially themselves from different viewing conditions. This is known as perceptual constancy.
Perceptual constancy may be constant in shape, size, color. Hold a familiar object, say a volleyball, bring it gradually close to you and then gradually far away from you. Its size does not change a great deal although the retinal image has become smaller. This is shape constancy.
A potted fern plant placed on a stage with a blue lighting will not be seen as blue, but it will be seen more or less as green so that it maintains its color constancy.
Interposition or superposition.
This occurs when an object covers part of another object so that the obscured object loses its contour and therefore appears to be farther away than it is.
Two objects of equal size wherein one object is placed farther in the foreground is visualized as smaller as projected in the retinal image.
A rectangular shape when moved in an acute angle will look thin and slender. A round-mouth object when moved farther will appear oval.
Stimulus that produces parallel lines or two straight lines with each other will always converge at the end point or towards the horizon. The converging line is perceived as far or distant away.
Perceptual motion happens when a stimulus is perceived to move according to the viewer. This can be the result of the body movement or movements of the objects surrounding the viewer.
Movements can be produced even when the body and object are not moving. A passenger who looks out at the side window of a vehicle while sitting may notice the outside frame view subsequently changing.
This motion simultaneously occurs with speed. The speed of the doer creates movement on the surrounding. Looming is in the enlargement in the size of an object or thing as it approaches the receiver. This is typical in ball games. A player throws, hits or strikes the ball so hard to create speed. The speed can deceive the opponent since he may not be able to notice it. In spite of the speed, the opponent is able to visualize the ball becoming big as it reaches him because of the looming effect.
Can be made by a swift alternation of immovable stimuli that stimulates movement, thus appearing as in real motion. For example, Christmas lights, animation films.
The object is presumed to be in motion in its relation to the surrounding frame, which is assumed to be not in motion. However, the object is not really the one moving, it is the change in the elements of the surrounding frame that cases the movement. For example, the moon appears to be moving when viewed at night. When in fact, it is the clouds that move across the moon. In cinematic effect, driver and vehicle not moving but the surrounding or environment has effects of it as moving.
|sense organ |sensation |stimuli |sensitivity |receptors |
|eyes |vision |lightwaves |intensity of wavelengths: |rods and cones (retina) |
| | | |hues, saturation, | |
| | | |brightness | |
|ears |audition |soundwaves |intensity of frequency: |organ of corti (cochlea) |
| | | |pitch, tone, loudness | |
|skin |somatic touch (tactile) |mechanical and thermal |cutaneous; pain; |free nerve ending |
|(dermis) | | |temperature; warm; cold; | |
| | | |pressure; touch (tactile) | |
|tongue |gustatory (taste) |solid and liquid |salt, sweet, sour, bitter |taste buds |
|nose |olfactory (smell) |gaseous state |basic smell |olfactory bulb |
|ear (inner ear – |vestibular (sense of |bodily movements |balance (equilibrium) |end of hair cells in the |
|semicircular canal) |balance) | | |semicircular canal |
|muscles, tendons, joints |kinesthetic |bodily movements |posture |nerve endings of muscles,|
| | | | |tendons, and joints |
The summary on how individuals see and hear is simplified in these pathways:
Stimulus cornea aqueous humor pupil lens (light)
vitreous humor retina photoreceptors electric potentials (rods and cones)
optic nerve optic chiasm cerebral cortex response (occipital)
Stimulus pinna auditory meatus external auditory (sound) (auricle) canal
tympanic membrane bony structure oval window cochlea (eardrum) (malleus, incus, stapes)
basilar membrane organ of corti electric potentials
auditory cerebral cortex response (temporal)
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