All information about the world come to us by way of our senses. The psychology of sensation is concerned with the ability of the sense organs to detect stimuli: lights, sounds, and other energies.
What are the 6 classes of energy?
1. The eye is sensitive to light energy.
2. The ear is stimulated by sound energy.
3. Mechanical energy, such as that coming from a tuning fork, is very effective in including feelings of vibration on the bony areas of the body.
4. Thermal energy is involved when we feel the temperature of a cold glass.
5. Chemical energy stimulates our nostrils and taste buds.
6. Electricity has the property of exciting all the sense channels.
What are some general properties of the senses?
1. Absolute thresholds
How much energy does it take to stimulate the eye, the ear, and the other sense organs? What is the least amount of energy that can be experienced? What is the least amount of energy that causes us to react to some particular stimulus?
When physical energy is below a certain level, the stimuli are not detected. When just above level, detection is possible. When stimuli are "just barely detected" we speak of this as the absolute threshold.
2. Difference threshold
Not only do thresholds vary from person to person, but in any given person, threshold readings may not be constant from day to day. For practical purposes, thresholds permit one to get fitted with hearing aids, function as taste teaser, or read conventional type. Threshold measurement always involves a statistical average of one kind or another. "Psychological" experience can be measured in "physical" quantities. Thus we speak of psychophysical measurement.
Psychophysical measurement involves determination of the "just noticeable difference", or j.n.d. for short. Thus, if we have 100-watt bulb giving off an amount of light, how much increase or decrease in intensity is necessary for an observer to detect a j.n.d? The just noticeable difference is called the difference threshold.
Equations relating sensory experience to the intensity of physical stimulus have proved helpful to engineers designing telephones, video displays, tape recorders, and other types communication equipment.
How does the brain mediate sensations of light?
Visual experience occur by pressure on the eyeball or electrical stimulation of certain areas of the brain which produce the sensation of light. The visible portion of the electromagnetic spectrum is called light because it is what usually produces sensation in the visual system.
Describe the human eye. How does it work?
The eye is sensitive to that portion of electromagnetic energy that we call light. The electromagnetic energy travels in waves, with wavelengths that vary from the shortest cosmic rays, 10-trillionths of an inch to long radio waves that may measure many miles.
A light ray entering the eye on its way to the retina passes through the following parts:
Cornea - a tough transparent membrane where the light enters
Aqueous humor - a watery fluid
Lens - a transparent body which focuses the light to the sensitive surface, the retina and whose shape can changed by the ciliary muscles.
Vitreous humor - a transparent jelly filling the interior of the eye.
Pupil - a small hole in the front of the eye which regulates the amount of light entering the eye. This is formed by the iris.
Iris - consists of a ring of muscles that can contract or expand, thereby controlling the pupil size. The iris gives the eyes their characteristic color (blue, brown, and so forth)
Retina - the part of the eye sensitive to light found at the back of the eye.
What are the 3 main layers of the retina?
1. Rods and cones - the photosensitive cells or photoreceptors that convert light into neural signals.
2. Bipolar cells - which make synaptic connections with the rods and cones.
3. Ganglion cells - the fibers of which form the optic nerve connected to the brain.
Fovea - the most sensitive portion of the eye in normal daylight vision. This is a part of the retina. It plays a major role in perception.
Blind spot - an insensitive area not far from the fovea where the nerve fibers from the ganglion cells of the retina come together for form the optic nerve.
The optic nerve fibers lead from each eye to the occipital lobes of the brain, where vision is represented. The optic nerve bundles from each eye, meet at the optic chiasma, where the nerve fibers from the inner, or nasal, half of the retina cross over and go to opposite sides of the brain. Thus stimuli falling on the right side of each retina are transmitted to the occipital cortex of the right cerebral hemisphere, and stimuli impinging on the left side of each retina are transmitted to the left cerebral hemisphere. This means that objects in the right visual field are imaged to the left cerebral hemisphere, while objects in the left visual field are imaged to the right hemisphere.
How do the rods and cones differ?
The cones, active only in daylight vision, permit us to see both achromatic colors: white, black, and the intermediate grays; as well as the chromatic colors: red, green, blue, and so forth.
The rods function mainly under reduced illumination: at twighlight or night. They permit us to see only achromatic colors.
We have all experienced the difficulty of finding our way to an empty seat when entering a dark theater. This is because it takes a long time for the eye to adjust from bright light to darkness.
What are the psychological dimenstions of color? How do we understand color blindness?
The chief dimensions of color are hue, brightness, and saturation.
Hue - refers to what we ordinarily think of as the "name" of the color as in red, green, etc.
Brightness - this is the energy of the light source.
Saturation - refers to the apparent purity of the color. Highly saturated colors appear to be pure hues, without any grays.
To understand color blindness, we may think of the normal eye as discriminating the 3 systems of color; light-dark, yellow-blue, and red-green. All other combinations can be derived from these. A deficiency in one or two of these systems results in color-blindness. The person with normal vision is called trichomat. A person who lacks one system but has use of the other two, is called dichromat and is partially colorblind. The person which only the light-dark system is mono-chromat and is totally colorblind. By far, the most common form of colorblindness is red-green blindness, with the blue-yellow and light-dark systems intact. Total colorblindess in which the person sees merely black, white, and gray, is extremely rare; yellow-blue blindness is rare still. Most color blind persons are unaware of their defect or color deficiency.
Describe the auditory sense
The ear is sensitive to mechanical energy, the pressure changes among molecules in the atmosphere. A vibrating object as that of a tuning fork, causes waves of compression and expansion among the air molecules surrounding it. Molecules vibrate the air, water, or some other medium. This vibration causes sound waves which are the stimuli for hearing.
A wave has two characteristics namely:
1. Frequency - This refers to the number vibrations per second or the number of complete cycle of the wave is repeated. The unit Hertz (Hz) is used to denote cycles per second.
2. Amplitude - This refers to the amount of compression and expansion of air, as represented by the height of the wave from base to crest.
What are the chief dimensions of auditory experience?
The chief dimensions of auditory experience are pitch and loudness.
Pitch - This is determined by the frequency of vibration of the sound waves.
Loudness - This is determined by the amplitude of these waves.
How do the same notes differ from one musical instrument to the other?
1. They differ in the number of overtones produced
2. They differ because of the construction of the instrument which enhances certain overtones.
These differences producing a characteristic quality of a musical tone is called timbre. Timbre tells us whether a tone is produced by a piano or a guitar.
What happens when two tones are sounded together?
Tones sounded together lead to a fusion that is pleasant or unpleasant. The two tones create a third tone which may or may not blend with the fundamental tones sounded. Complex sounds not in harmonious relation to one another are called noise.
Describe the structure of the human ear.
The auditory apparatus, the ear, consists of the external ear, leading by way of the auditory canal to the eardrum, which is next to the middle ear. The bones of the middle ear such as hammer, stirrup and anvil, transmit the sound waves to the oval window, leading to the inner ear. The cochlea houses the receptors of the inner ear consisting in the basilar membrane. Wave motions in the fluid of the inner ear agitates these hair cells, which in turn activate the auditory nerve.
What are the other senses?
These are the "lower senses" which include smell, taste, the four skin sensations, kinesthesis, and the equilibratory senses.
Smell - is the most primitive and most important of the senses. It has a more direct route to the brain than any other sense.
Taste - consist of the primary qualities: sweet, sour, salty and bitter. Other taste experiences are composed of fusion's of these qualities. The taste receptors are found in the taste buds. The number of taste buds decrease with age. In general, sensitivity to sweet is greatest at the tip of the tongue, to salty on the tip and sides, to sour on the sides, and bitter on the back.
Skin sensations - include pressure, pain, warm, and cold. All other skin sensations are variations of the four basic sensations. They are described as itch, tickle, quick-pricking pain, or dull long-lasting pain.
Kinesthesis - a sensory system that informs us of the position and movement of parts of the body: muscle, tendon, and joint sense. Without kinesthesis we would have great difficulty in maintaining, posture and in walking, climbing, and controlling other movements like reaching and grasping.
Equilibratory senses - cooperates with the kinesthesis. The equilibratory senses deal with total body position in relation to gravity and with motion of the body as a whole. The sense organs for equilibrium are located in the inner-ear.
