The absolute threshold is the point where something becomes noticeable to our senses. It is the softest sound we can hear or the slightest touch we can feel. Anything less than this goes unnoticed. The absolute threshold is therefore the point at which stimuli goes from undetectable to detectable to our senses.
Difference Threshold:
Once a stimulus becomes detectable to us, how do we recognize if this stimulus changes. When we notice the sound of the radio in the other room, how do we notice when it becomes louder. It's conceivable that someone could be turning it up so slightly that the difference is undetectable. The difference threshold is the amount of change needed for us to recognize that a change has occurred. This change is referred to as the Just Noticeable Difference.
This difference is not absolute, however. Imagine holding a five pound weight and one pound was added. Most of us would notice this difference. But what if we were holding a fifty pound weight? Would we notice if another pound were added? The reason many of us would not is because the change required to detect a difference has to represent a percentage. In the first scenario, one pound would increase the weight by 20%, in the second, that same weight would add only an additional 2%. This theory, named after its original observer, is referred to as Weber's Law.
Signal Detection Theory:
Have you ever been in a crowded room with lots of people talking? Situations like that can make it difficult to focus on any particular stimulus, like the conversation we are having with a friend. We are often faced with the daunting task of focusing our attention on certain things while at the same time attempting to ignore the flood of information entering our senses. When we do this, we are making a determination as to what is important to sense and what is background noise. This concept is referred to as signal detection because we attempt detect what we want to focus on and ignore or minimize everything else.
Sensory Adaptation:
The last concept refers to stimuli which has become redundant or remains unchanged for an extended period of time. Ever wonder why we notice certain smells or sounds right away and then after a while they fade into the background? Once we adapt to the perfume or the ticking of the clock, we stop recognizing it. This process of becoming less sensitive to unchanging stimulus is referred to as sensory adaptation.
Hearing
Hearing (or audition; adjectival form: "auditory" or "aural") is one of the traditional and most important five senses. It is the ability to perceive sound by detecting vibrations via an organ such as the ear. The inability to hear is called deafness.
Sound is...
A vibration or wave of air molecules caused by the motion of an object. The wave is a compression wave where the density of the molecules is higher. This wave travels through the air at the speed dependent on the temperature. A sound wave contains energy, which in turn means it can make things move. However, if the wave strikes something solid, the wave will bounce back--an echo. Sound energy can be changed into other forms of energy e.g. electrical energy, and vice versa; this is one of its properties that allow us to communicate by telephone.
Sound vibration is...
Sound is produced when an object moves or vibrates. Without movement there will be no sound. When an object moves or vibrates, the air molecules around the object also vibrate. Vibrating object (as long as they are not in a vacuum) produces sound. Sound travels at different rates in different media. In dry air, sound travels at 331.6 metres per seconds. Each molecule moves back and forward only a tiny distance, but it is enough to cause the air particles to bump into each other. This creates areas where there are many molecules pushed close together--compression; and areas where molecules are spread far apart--rarefactions. These compression and rarefactions move outwards away from the sound source in circles. A sound wave is created when a series of these pressure changes waves move through the air.
Physical characteristics...
Any simple sound, such as a musical note, may be completely described by specifying three perceptual characteristics: pitch loudness (or intensity) and quality (or timbre).These characteristics correspond exactly to three physical characteristics: frequency, amplitude and harmonic constitution, or waveform, respectively. Noise is a complex sound, a mixture of many different frequencies or notes not harmonically related.
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Sound needed a medium...
By the means of a medium or sound carrier, sound travels from a vibration object to your ear. A solid, a liquid or a gas can be the medium, when there are on medium to carry the sound to our ear, we cannot hear the sound. E.g. astronauts at the moon cannot communicate directly to each other. They can only speak to each other by radio. This is because the moon has no air.
Speed of sound...
The speed of sound depends on the medium. For example, in the air sound travels at the speed of about 335 metres (6100 feet) a second. Sound travels about 4 times as fast in water as it does in air. Sound travels even faster in solids. In steel and in aluminium, the speed is about 15 times faster than it is in air.
Properties of Sound:
Frequency....
The rate of vibration of a sound wave, measured in hertz (Hz), which equals the number of complete vibrations per sound. The distance from a point on an angle on a similar point on the next vibration is called the wavelength, measured in metres. Different animals can hear different ranges of frequencies.
A sound wave with a low frequency is heard as a low note, ---a low pitch. As the frequency of a sound increases, the pitch of the sound increases. Musicians refer to the pitch of a note to describe how high or low it is. An oscilloscope is a device which displays various waves
Amplitude....
The strength of a sound wave: loud sounds have large amplitude. Sound producing objects that vibrate over a greater distance give sounds with longer amplitude. The loudness of a sound is often described as its amplitude but they are not quite the same thing. The loudness of a sound depends on the hearing ability of the listener. A sound of particular amplitude may sound loud to one person and quiet to another.
Intensity...
The distance as which a sound can be heard depends on its intensity, which is the arc rate of flow of energy per unit area perpendicular to the direction of propagation. Intensity varies inversely as the square of the distance in the actual propagation of sound through the atmosphere, changes in the physical properties of the air like temperature, pressure and humidity, produce damping and scattering of the directed sound waves :so that the inverse-square law generously is not applicable in direct measurements of the intensity of sound.
Quality/Timbre....
The quality of a musical sound depends on the precise shops of the waveform. The figure (a) below illustrates the waveform of a tuning fork. It is a pure sine curve. A musical instrument producing the same frequency is shown in Fig (b).The difference in shape is responsible for giving the instrument its particular quality.
Like your other sense organs, your ears are extremely well-designed. In fact, they serve two very important purposes. Do you know what they are? You were probably able to figure out that your ears help you to hear sounds, but what you probably did not know is that your ears also help you to keep your balance.
How You Hear:
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When an object makes a noise, it sends vibrations (better known as sound waves) speeding through the air. These vibrations are then funnelled into your ear canal by your outer ear. As the vibrations move into your middle ear, they hit your eardrum and cause it to vibrate as well. This sets off a chain reaction of vibrations. Your eardrum, which is smaller and thinner than the nail on your pinky finger, vibrates the three smallest bones in your body: first, the hammer, then the anvil, and finally, the stirrup. The stirrup passes the vibrations into a coiled tube in the inner ear called the cochlea.
The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into messages that are sent to the brain via the auditory nerve. The auditory nerve carries messages from 25,000 receptors in your ear to your brain. Your brain then makes sense of the messages and tells you what sounds you are hearing.
How You Keep Your Balance:
Near the top of the cochlea are three loops called the semi-circular canals. The canals are full of liquid also. When you move your head, the liquid moves. It pushes against hair like nerve endings, which send messages to your brain. From these messages, your brain can tell whether or how your body is moving.
If you have ever felt dizzy after having spun around on a carnival ride, it was probably because the liquid inside the semicircular canals swirled around inside your ears. This makes the hairs of the sensory cells bend in all different directions, so the cells' signals confuse your brain.
Ear Problem: Deafness
Deafness is second perhaps only to blindness in the difficulties which it may cause in sensing and perceiving our world. Obviously, much of the communication between people is verbal, not written (as we discuss in the Language and Communication Chapter). Until the invention of small, transistorized hearing aids, people with hearing problems were less well-off than those with visual problems.
Examination of the ear drawing suggests two means by which deafness may be caused. Sound impulses are transmitted mechanically from the auditory canal until they stimulate the hair cells. Interfering with any portion of this mechanical process causes conduction deafness. Such deafness decreases your sensitivity to tones of all frequencies.
The second means of conduction involves the hair cells and auditory nerve as well as parts of the central nervous system.
Interference with, or deterioration of, the nerves cause nerve deafness. Nerve deafness usually hinders your perception of high-frequency sounds most, but it also somewhat reduces your sensitivity to low-frequency sounds.
Facts:
Children have more sensitive ears than adults. They can recognize a wider variety of noises.
Dolphins have the best sense of hearing among animals. They are able to hear 14 times better than humans.
Animals hear more sounds than humans.
Perception
We have learned in vision why lemon appears to be yellow. But why do we think of it as having a spherical shape, like that of a ball? That’s the perception which is the process by which sensory information is analyzed by the brain. Perception comes after sensation as a response or involuntary reaction. When we see the lemon, signals flow from your eyes to our brain (sensation) then the information is interpreted and organized in the brain so we recognize the lemon shape (perception). Knowledge and experience are extremely important to perception, because they help us make sense of the input to our sensory systems.
Much of our understanding of how and why we perceive things comes from Gestalt psychology.
For example - one of the most well known Gestalt principles is the Phi Phenomenon, which is the illusion of movement from presenting stimuli in rapid succession. When you see a cartoon or running Christmas lights, you see movement (although none actually exists) because of this principle.
Gestalt Principles of Perceptual Organization
1) figure-ground - this is the fundamental way we organize visual perceptions. When we look at an object, we see that object (figure) and the background (ground) on which it sits. For example, when I see a picture of a friend, I see my friends face (figure) and the beautiful Sears brand backdrop behind my friend (ground).
2) Simplicity (good form) - we group elements that make a good form. However, the idea of "good form" is a little vague and subjective. Most psychologists think good form is whatever is easiest or most simple. For example, what do you see here: : > )
Do you see a smiling face? There are simply 3 elements from my keyboard next to each other, but it is "easy" to organize the elements into a shape that we are familiar with.
3) Proximity - nearness=belongingness. Objects that are close to each other in physical space are often perceived as belonging together.
4) Similarity - do I really need to explain this one? As you probably guessed this one state that objects that are similar are perceived as going together. For example, if I ask you to group the following objects: (* * # * # # #) into groups, you would probably place the asterisks and the pound signs into distinct groups.
5) Continuity - we follow whatever direction we are led. Dots in a smooth curve appear to go together more than jagged angles. This principle really gets at just how lazy humans are when it comes to perception.
6) Common fate - elements that move together tend to be grouped together. For example, when you see geese flying south for the winter, they often appear to be in a "V" shape.
7) Closure - we tend to complete a form when it has gaps.
Illusion: is a distortion of a sensory perception. Each of the human senses can be deceived by illusions, but visual illusions are the most well known. Some illusions are subjective; different people may experience an illusion differently, or not at all.
Television is an example of an illusion. When you see a person on the screen, there isn't actually a person there.
Finally, Sensation and Perception topic is really important to all of us and we should protect and keep our five senses fine in order to perform their tasks perfectly.
