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(p)Psych: Sensation and perception


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How does the visual system work?
The visual system works on sensing and perceiving light waves. Light waves vary in their length and amplitude.

Perception according to Gestalt Psychology.
Much of our understanding of how and why we perceive things comes from Gestalt Psychology
Gestalt psychologists have developed a number of Principles of Perceptual Organization.
Where are the majority of cones located?
Most are located in the center of the retina...called the FOVEA, which is a tiny spot in the center of the retina that contains ONLY cones...visual acuity is best here.

SO...when you need to focus on something you attempt to bring the image into the fovea.

Describe the opponent-process theory of color vision.
The red-green, blue-yellow, and black-white color combinations compete against each other to produce color vision.
Difference Threshold?
Difference Threshold - the minimum amount of stimulus intensity change needed to produce a noticeable change.

the greater the intensity (ex., weight) of a stimulus, the greater the change needed to produce a noticeable change.

For example, when you pick up a 5 lb weight, and then a 10 pound weight, you can feel a big difference between the two. However, when you pick up 100 lbs, and then 105 lbs, it is much more difficult to feel the difference.
What is an illusion?
Illusions - an incorrect perception caused by a distortion of visual sensations.
Selective Attention?
Selective Attention - process of discriminating between what is important & is irrelevant (Seems redundant: selective-attention?), and is influenced by motivation.

For example - students in class should focus on what the teachers are saying and the overheads being presented. Students walking by the classroom may focus on people in the room, who is the teacher, etc., and not the same thing the students in the class.
What three steps are necessary for sensation?
2) Sensory transduction
3)info travels down to neural pathways.
Wave amplitude?
Wave amplitude (this is the size/height of the wave) - affects brightness perception.
Describe the Trichromatic Theory of colour vision.

Trichromatic Theory - this theory indicates that we can receive 3 types of colors (red, green, and blue) and that the cones vary the ratio of neural activity (Like a projection T.V.). The ratio of each each color to the other then determines the exact color that we see.
Retina - inner membrane of the eye that receives information about light using rods and cones. The functioning of the retina is similar to the spinal cord - both act as a highway for information to travel on.

List several monocular cues for depth perception.
Relative size, linear perspective, overlap, aerial haze, and texture gradients.
Threshold - a dividing line between what has detectable energy and what does not.

For example - many classrooms have automatic light sensors. When people have not been in a room for a while, the lights go out. However, once someone walks into the room, the lights go back on. For this to happen, the sensor has a threshold for motion that must be crossed before it turns the lights back on. So, dust floating in the room should not make the lights go on, but a person walking in should.
Describe the Gestalt Perceptual Principle of closure.
7)closure - we tend to complete a form when it has gaps.
Perceptual Expectancy?
Perceptual Expectancy - how we perceive the world is a function of our past experiences, culture, and biological makeup.
Ex: you may look at a painting and not really understand the message the artist is trying to convey. But, if someone tells you about it, you might begin to see things in the painting that you were unable to see before.
Describe the function of rod photoreceptors.
Rods are important for vision at night. They cannot detect color.
Pupil - opening at the center of the iris which controls the amount of light entering the eye. Dilates and Constricts.
Describe the Gestalt Perceptual Principle of proximity.
3) proximity - nearness=belongingness. Objects that are close to each other in physical space are often perceived as belonging together.
Wave length?
Wave length (also referred to as frequency, since the longer a wave, the less often/quickly it occurs) - affects color perception (ex., red=approx 700, yellow approx 600)
Define sensory adaptation.
Sensory adaptation happens when the sensory receptors ignore constant stimulation.
Def'n the study of Psychophysics?
Psychophysics can be defined as, the study of how physical stimuli are translated into psychological experience.

In order to measure these events, psychologists use THRESHOLDS.

Describe the Gestalt Perceptual Principle of continuity.
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.
Def'n Perception
Perception can be defined as the active process of selecting, organizing, and interpreting the information brought to the brain by the senses.
Describe the function of cone photoreceptors.
Cones are important for color vision in bright light.
Cornea - the round, transparent area that allows light to pass into the eye.
How many colour specific cones does the eye have?
We can see many colors, but only have 3 types of cones that receive information about color. We have cones that pick up light waves for red, green, and blue.
Explain the Signal-Detection Theory.
The Signal-Detection Theory asserts-detection of a stimulus involves some decision making process as well as a sensory process. Additionally, both sensory and decision making processes are influenced by many more factors than just intensity.

a) Noise - how much outside interference exists.

b) Criterion - the level of assurance that you decide must be met before you take action. Involves higher mental processes. You set criterion based on expectations and consequences of inaccuracy.

For example - at a party, you order a need to pay attention so that you will be able to detect the appropriate signal (doorbell), especially since there is a lot of noise at the party. But when you first order the pizza, you know it won't be there in 2 minutes, so you don't really pay attention for the doorbell. As the time for the pizza to arrive approaches, however, your criterion become more focused on the doorbell and less on extraneous noise.
Define sensation
Sensations can be defined as the passive process of bringing information from the outside world into the body and to the brain. The process is passive in the sense that we do not have to be consciously engaging in a "sensing" process.
Ratio of Rods and Cones?
Rods & Cones - many more rods (approximately 120 million) than cones (approx 6.4 million).
Fast Pathways for pain perception?
1) fast pathways - registers localized pain (usually sharp pain) and sends the information to the cortex in a fraction of a second. EX. - cut your finger with a knife.
Cones - visual receptor cells that are important in daylight vision and color vision.
Cones work well in daylight, but not in dim lighting. This is why it is more difficult to see colors in low light.
What is convergence?
Convergence happens when the eyes turn inward so they can both focus on an object. This is important for binocular depth perception.
Rods-visual receptor cells that are important for night vision and peripheral vision.

the rods are better for night vision because they are much more sensitive than cones.
Describe the Gestalt Perceptual Principle of simplicity/pragnanz (good form).
2) simplicity/pragnanz (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 what ever 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.
Lens - the transparent structure that focuses light onto the retina.
Describe size constancy.

Size constancy means that our senses know that the size of an object stays constant even though it may appear smaller when it is far away.
How is the distribution of rods conducive to peripheral vision?
Rods are better for peripheral vision because there are many more on the periphery of the retina. The cones are mostly in and around the fovea but decrease as you go out.
To see best at night, look just above or below the object...this keeps the image on the rods.
How do expections influence pain perception?
1) expectations - research shown that our expectations about how much something will hurt can effect our perception.

Melzack - indicated that believing that something will be very painful helps us prepare for it.

For example - child birth: Lamaze method falsely leads us to believe it won't be painful. Maybe if we know it will be bad we can adequately prepare to handle it.
How do sensation and perception work together?
1) Sensation occurs:
a) sensory organs absorb energy from a physical stimulus in the environment.
b) sensory receptors convert this energy into neural impulses and send them to the brain.
2) Perception follows:
a) the brain organizes the information and translates it into something meaningful.
What is the term for describing how "sharp" or focussed someone's vision is?
Visual acuity
Perception involves the converting of sensory info into something meaningful, but what def'ns meaningful?
This involves selective attention and perceptual expectancy.
Describe the Opponent-Process Theory of colour vision.
Opponent-Process Theory - color perception depends on the reception of pairs of antagonist colors. Each receptor can only work with one color at a time so the opponent color in the pair is blocked out. Pairs = red-green, blue-yellow, black- white (light-dark).
What is the depth perception cue where each eye sees a slightly different perspective of an image?
Retinal disparity, which is sometimes called binocular disparity.
Muller-Lyer Illusion?
Although many theories exist for this illusion, there is no certain explanation. One theory is based on eye movement. When the arrows point inwards, our gaze rests inside the angles formed by the arrows. When they point outwards, our eyes demarcate the entire perspective and our gaze rests outside the angles. The outward pointing arrows make the figure more open and so the horizontal line appears longer.
<-> vs >-<
What is the term that refers to a stimulus amplitude where something is detected 50% of the time?
Absolute threshold
List the Gestalt Principles of Organization.
Gestalt Principles of Perceptual Organization:
1) figure-ground
2) simplicity/pragnanz
3) proximity
4) similarity
5) continuity
6) common fate
7) closure
Describe the two-factor theory of color vision.
The processes described by the trichromatic theory happen in the retina. The opponent-process theory processes take place in the thalamus. Both of these are correct but happen in different parts of the brain.

Reversible Figures?
Reversible Figures - ambiguous sensory information that creates more than 1 good form. For example, the picture of two faces looking toward each other that is also a vase.
In which Gestalt law do we fill in the missing information from a stimulus?
The Gestalt law of closure.
Describe the Gestalt Perceptual Principle of figure-ground.
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).
What part of the eye converts light into a neural signal?
The retina.
Describe the Gestalt Perceptual Principle of similarity.
4) similarity - this one states 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.
Name the hole in the middle of the eye that regulates the amount of incoming light.
The pupil.
What are the three factors which influence an individual's pain perception?
The perception of pain is not the automatic result of pain perception. Expectations, personlity, and mood can effect on the amount of pain percieved.
What is the term for a stimulus that is below the absolute threshold?
List perceptual Illusions.
Ambiguous figures
Figure ground reversal patterns
impossible objects
Moon Illusions
Phi phenomenon
Muller-Lyer Illusion
Ponzo Illusion
Autokinetic effect
Purkinje shift
Describe the trichromatic theory of color vision.
The red, green, and blue sensitive cones are responsible for color vision.
Impossible Figures?
Impossible Figures - objects that can be represented in 2-dimensional pictures but can not exist in 3-dimensional space despite our perceptions. You know the artist, Escher who draws the pictures like...the hands drawing each other, the waterfall that goes down and stays level at the same time, etc...
Pain is an unpleasant yet important function for survival: warning system (but not all pain is needed for survival).
Describe the Gestalt Perceptual Principle of common fate.
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.
Pain perception: The gate control theory.
Gate Control Theory (Melzack & Walls, 1965) - incoming pain must pass through a "gate" located in the spinal cord which determines what information about pain will be sent to the brain. So, it can be opened to allow pain through or closed to prevent pain from being perceived.
How does mood influence the perception of pain?
Bad moods, angry, unhappy, etc, can lead to the experience of increased pain.
For example - study manipulated moods of subjects then asked them to complete questionnaires of pain perception. Those in negative mood group reported significantly more pain than other subjects.
How does personality influence the perception of pain?
People with negative types of personalities often have more pain. For example - a very uptight person may experience muscle pains, back pains, etc.
Name the two pathways upon which the perception of pain depends.
There are two different pathways to the brain on which pain can travel - information brought from free nerve endings in the skin to the brain via two different systems:
1) fast pathways
2) slow pathways
Describe "the gate's" mechanics.
The Gate - actually a neural network controlled by the brain. Located in an area of the spinal cord called the Substansia Gelatinosa. There are two types of nerve fibers in this area:
a) large - sends fast signals and can prevent pain by closing the gate.
b) small - sends slower signals which open the gate. So - when pain occurs it is because the large fibers are off and the small are on, opening the gate.
Since the gate is controlled by the brain, expectations, mood, and personality influence the functioning of the gate.
Phi Phenomenon?
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.
Slow pathways for pain perception?
2) slow pathways - sends information through the limbic system which takes about 1-2 seconds longer than directly to the cortex (longer lasting, aching/burning).

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