PERCEPTION

SENSATION AND PERCEPTION

The distinction between Sensation and Perception:

Although closely related, sensation and perception play two complimentary but different roles in how we interpret our world Psychologists distinguish between sensation and perception:
1-Sensation is the stimulation of sense organs
Perception is the selection, and interpretation of sensory input.
2- Sensation involves the absorption of energy, such as light or sound waves by sensory organs, such as the eyes and ears Perception involves organization and translating sensory input into something meaningful ..
Normally, the processes of sensation and perception are difficult to separate because people automatically start organizing incoming sensory stimulation the moment it arrives .Although the distinction between sensation and perception has been useful in organizing theory and research , but in operation the two processes join together .

Sensation

Our knowledge of the world comes though our senses ;our sense translate information or stimuli about the world into neural activity for interpretation by the brain .The messages about stimuli which received by the brain are called sensation.
There are large amount of information is being sensed at any one time, such as room temperature, brightness of the lights, someone talking, or the smell of perfume. However with this majority amount of information ;but we can only sense those things we are able to sense. For examples we cannot notice radio waves, x-rays,..
So we can define sensation as the process by which stimuli are detected, indentified, and measured

Sensory processes:

No matter when sensation is being described ,a certain sequence of events appears necessary for the sense to operate.
First some stimulus appropriate to that sense must be present in sufficient strength to begin reception .
Second the signal is picked up by a receptor (which is a nerve ending specialized for such a task) and transmitted through the sensory (or somatic)peripheral nervous system to the brain .
Third the signal activates a particular part of the brain that records the signal as a sensation .
It is important to recognize that humans have more than the "basic five "senses that are usually used., but it is probably more appropriate to recognize a "basic seven senses "which are vision ,hearing, touch, taste ,smell, balance ,kinesthesia


Absolute Threshold
In order to understand how people sense the external world ,psychologists try to determine how much of a stimulus is necessary for a person to sense it at all ? How much energy is required for someone to hear a sound or to see alight ???
To answer such questions psychologists studied this phenomenon and called it Absolute Threshold
So we can say that Absolute Threshold is the smallest amount of energy that will produced sensation, or it defined as the smallest intensity of stimulus that must be present for it to be detected. Threshold is the point where something becomes noticeable to our senses .
Stimuli that fall below this threshold and are usually not detected are referred to as subliminal stimuli (subconscious). Stimuli that are detected because they are above the threshold are called supraliminal stimuli (conscious)

Examples of absolute thresholds :

By using the definition of absolute threshold, investigators found that under ideal conditions, human abilities to detect weak stimuli are greater than esteemed.
For example, on a clear, dark night ,in the absence of other distracting lights ,you could see the light of the candle burning 30miles in the distance ! Of course ,we are talking about ideal conditions ,you would have to go out to the middle of nowhere to find the darkness required to put this statement to a suitable test !

Some actual examples of the absolute threshold for various senses can be seen in the following figure


Sense absolute threshold VisionA candle flame seen at 30 miles on a dark clear night  HearingThe tick of a watch under quiet conditions at 20 feet TasteOne teaspoon of sugar in two gallons of water  SmellOne drop of perfume diffused into whole dimension of a six room apartment TouchThe wing of a fly falling on your cheek from a distance of 1 centimeter 
Difference threshold(JND):

Another type of threshold is the difference threshold(also known) just noticeable difference(JND) .
It refers to smallest change or smallest difference in stimulus intensity that a specific sense can detect
Suppose you hear a sound of radio in the other room, how you can hear this sound when it becomes louder.We can imagine that someone could be turning it up so slightly that the difference is undetectable.
So we can say that the (JND) is the amount of change needed for us to recognize that a change has occurred.


Weber's Law.:
The (JND) is close cousins of absolute threshold .In fact , an absolute threshold is simply the just noticeable difference from noting (no stimulus input) to something.
Probably you might think that the JND would always have the same value for any given sense
Imagine you are holding a five pound weight and one pound was added. Certainly you would notice this difference. But what if you were holding a fifty pound weight? Would you notice if another pound were added? The answer ;no because the JND is greater for heavy objects than for alight ones; and the change required to detect a difference has to represent a percentage. In the first one , one pound would increase the weight by 20%, in the second, that same weight would add only an additional 2%. This principle , named after its original observer, is referred to as Weber's Law
Weber's Law states that the size of a just noticeable difference is a constant proportion of the size of the primary stimulus

Sensory adoption

Psychologists have focused on people's responses to changes in stimuli because they have found that the senses are tuned to change : they are most responsive to increases and decreases to new event rather than to ongoing , unchanging stimulation .This is because our sense have a general ability to adapt ,or adjust themselves ,to a constant level of stimulation. They get used to a new level and respond only to changes away from it.
A good example of this process of adaptation is the increase in visual sensitivity that you experience after a short time in a darkened movie theater .At first you see only blackness ,but after a while your eyes adapt to the new level ,and you can see seats ,faces ,and so on . Adaptation occurs for the other senses as well Receptors in your skin adapt to the cold water when you go for a swim ;disagreeable odors in a lab seem to disappear after awhile ;street noises stop to bother you after you've lived in a city for a time .Without sensory adaption ,you would feel the constant pressure of the clothes on your body, and other stimuli would seem to be bombarding all your senses at the same time..

PERCEPTION :

Perception: is a mental process of acquiring, interpreting, selecting, and organizing  HYPERLINK "http://en.wikipedia.org/wiki/Sense" \o "Sense" sensory  HYPERLINK "http://en.wikipedia.org/wiki/Information" \o "Information" information.

As mentioned in the introduction, perception refers to interpretation of what we receive through our senses.Therefore sometimes perception effected by our personal experience.
This means perception is a learned characteristic of behavior.
Research evidence indicates that a subjects whose perceptual experience is restricted, will be unable to develop normal perceptual reactions.

Suppose you were flying in an airplane , several thousand feet above the ground , on a clear day .The cares ,houses, and trees below would appear doll -size or smaller(sensation ),but you would realize they were normal size (perception )

Perceptual processes:

The study of perception deal with two functions of perceptual system :
1. Localization
2. Recognition


These functions carried out by different brain regions e.g. Localization occurs in the outer layers of brain cortex ,while recognition occurs in the inner layers of cortex.

Localization is the way we use to navigate through our environment, while recognition means what an objects is.

Attention:

Attention is the process of directing and focusing certain psychological incomes,( usually by voluntary control) , to enhance perception ,performance ,and mental experience .

Types of attention :

1- Selective Attention:
Selective attention is the tendency to focus on some stimuli in the environment while ignoring others .Attention can be voluntarily guided by motivation and a knowledge of what sources of information are important to the task at hand

2- Divided Attention :

Although attention resources are limited, people can sometimes divide their attention between two tasks. It is easier to divide attention between two practiced or automatic tasks (for examples ,tying a shoe while chewing gum ). Attention can also be divided when different sensory system are utilized to accomplish each task (such as writing while watching TV)

3- Involuntarily attention: Some times, the aspects of the environment may attract our attention involuntarily.

Factors influence perception :

Two types of factors influence perception: external(stimulus )cues and internal(personal)cues.:
Both internal and external cues affect the way in which a subject will pay attention to ,or attend to a stimulus .A subject must pay at least some attention to a stimulus in order to perception to occur.


External Cues :

External cues develop from the properties of a stimulus or groups of stimuli. Interest in the effects of external stimuli on perceptual development; arose during the early years of Gestalt psychology .
The Gestalt psychologists emphasized some principles of perceptual organization. These principles are :
1.Figure and ground :Our perceptual processes actively try to assign some stimuli to the foreground (figure )and some to the meaningless background ( ground).Figure-ground relationships are called unstable if the figure can sometimes be perceived as the ground and the ground can sometimes be perceived as the figure. Figures may also be described as ambiguous if they can be "correctly" interpreted in more than one way.




2. intensity :The more intensive stimulus ,the more likely a subject will pay attention to it .However., extremely high values may cause distortion in perception

3.Grouping of Object: According to Gestalt psychologists , We see figure via principles of grouping .These principles are:

A: proximity: Elements that are near one to another perceived as a whole. The black dot in the figure bellow could be grouped into vertical columns or horizontal rows .however, people tend to perceive rows because the effect of proximity (the dotes are closer together horizontally) .

 SHAPE \* MERGEFORMAT 


B:similarity:People tend to group similar stimuli together. This principle is apparent in the figure bellow ,where viewers group elements of similar lightness into the number two




C: Closure: People often group elements to create a sense of closure ,or completeness .Thus ,you may" complete" figures that actually have gapes in them . This principle is demonstrated in the figure below





D:continuity :This principle reflects people 's tendency to follow in whatever direction they have been led . Thus people tend to connect points that result in straight or gently curved lies that create ((smooth )) paths as shown bellow

Internal Cues :

Internal cues appear to be a function of a subject's cognitive processes .For example the motivation of a subject's, past experience ,and the expectations of the subject may all act as internal cues:

A: Motivation :Perception is frequently influenced by the motivation of the subject. This may result from the subject's physiological condition or social experience .A subject may have learned to give special attention to stimuli that reinforce or satisfy the motive condition .If the subject is never motivated to perceive a certain stimulus, he(she) will tend to ignore the stimulus .

B: Past experience :Previous learning can make a subject predict the meaning of future stimulus situations .Such anticipations may be correct or incorrect .

C: Set: Set is defined as a temporary tendency (or expectancy) to respond in a certain fashion .This tendency may change as the subject is confronted with different instructions or rewards .

Perceiving Distance

Two dimensional location :This ability lets us to determine whether a stimulus is coming from the right or left ,from above or below
Depth perception: which allows us to experience world in three dimensions .It involves interpretation of visual cues that indicate how near or far away objects are. This can be classified into types : binocular(two-eyes) and monocular (one-eye)cues

Perceptional Constancy:

Size Constancy:


Shape Constancy:

Brightness Constancy :

Unusual perceptual experiences :
Illusions:
Sometimes stimuli can be interpreted incorrectly .Some stimuli exist in a configuration that almost leads to incorrect perception .When this occurs, the perception is described as an illusion.
We can define illusion as perceptions that are misrepresentation of reality. For example which lines are longer in the following figure ?



A possible explanation of this type of illusion is that even though the pattern are two dimensional ;your brain treat them as three dimensional .These illusions have features that usually indicate distance in three dimensional space (Muller illusion )

Extrasensory perception

Extrasensory perception (ESP) is said to have occurred when a correct interpretation or manipulation of the environment has taken place without any information being provided by regular sensory processes.
Scientists have been investigating ESP /.They called this phenomenon (parapsychology). Several types of ESP have been studied including:
1- Telepathy: Is the transfer of thought from one person to another without the aid of usual sensory channels.
2- Precognition: Refers to the ability to anticipate (predict )
future events
3- Clairvoyance: Is the ability to disclose information that could not have been received by regular sensation ( visual perception of object that is covered or sealed)
4- Psychokinesis (PK): Is the capacity for making objects move by using only thought processes ( without touching them)


Extremes of sensory load:
Sensory deprivation(very little stimulation )or Sensory overload (a great amount of stimulation) may exceed the person's "normal "capabilities for sensory adaption .When this happens ,unusual patterns of responding (such as hallucinations)may result .It seems that people are unable to continue to correctly interpret the stimulus environment if extreme sensory overload or extreme sensory deprivation is maintained over a prolonged period of time.









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