perception is the process of understanding and interpreting sensations.
The study of the interaction between sensations and our experience of them is called psychophysics.
Researchers trying to uncover the rules our minds use to interpret sensations.
We will look at some basic perceptual rules for vision.
Research shows that our senses have limits.
The smallest amount of stimuli we can detect is the absolute threshold.
A single candle flame is estimated to be the smallest amount of light we can detect, which is 30 miles away on a dark night.
A single drop of perfume could be detected by most of us.
The technical definition of absolute threshold is the minimal amount of stimuli we can detect, because researchers try to take into account individual variation in sensitivity and interference from other sensory sources.
Stimuli below our absolute threshold is said to be subliminal.
Some companies claim that they can change behavior.
Their claim is not supported by psychological research.
Sometimes subliminal messages can affect behavior in subtle ways, such as choosing a word at random from a list after the word was presented subliminally.
There is no evidence that subliminal messages such as "lose weight" are effective.
The placebo effect is more likely to change behavior than the subliminal message is.
This change is defined by the difference threshold.
The difference threshold is the smallest amount of change needed before we can detect a change.
The Weber-Fechner law is named after psychophysicist Gustav Fechner and is named after Weber's law.
The change needed is proportional to the original intensity.
It will need to change before we notice a difference.
If someone adds a small amount of cayenne pepper to a dish that is normally not very spicy, you would need to add a lot more hot pepper to make it more spicy.
Weber discovered that the constants differ between the senses.
5 percent is the constant for hearing.
If you listened to a 100decibel tone, the volume would have to increase to 105 decibels before you noticed that it was louder.
Weber has a constant vision of 8 percent.
Adding 8 candles to 100 candles would make it look brighter.
Several theories are used by psychologists to describe how we see the world.
These theories are not competing with each other.
There are different examples or parts of perception described in each theory.
Sometimes a single example of the interpretation of sensation needs to be explained using all of the following theories.
Real-world examples of perception are more complex.
The effects of distraction and interference on our perception of the world is investigated by signal detection theory.
Predicting what we will perceive among competing stimuli is the focus of this area of research.
The motivation to detect certain stimuli and what we expect to see are taken into account in signal detection theory.
The factors are called response criteria.
If I am hungry and enjoy the taste of rhubarb, I will be more likely to smell a freshly baked pie.
signal detection theory tries to explain and predict the different perceptual mistakes we make.
A false positive is when we think there isn't anything.
You may think you see a friend on a crowded street and end up waving at a stranger.
A false negative is not seeing something.
The directions at the top of the test tell you not to write on the form.
One type of error is more serious than the other, and this can affect perception.
A false negative is a more serious mistake than a false positive, even though both mistakes are important.
When we use top-down processing, we fill in gaps in what we see.
I _ope yo_ _et a 5 on t_ A_ e_am.
You used the context of the sentence to see the blanks as the right letters.
When you use your background knowledge, you fill in gaps in what you see.
Our experience makes mental representations of how we expect the world to be.
The world is influenced by how we perceive it.
A perceptual set is a predisposition to perceive something in a certain way.
You have experienced top-down processing if you have seen images in the clouds.
You can use your background knowledge to see the random shapes of clouds.
Backmasking was a concern of some parent groups in the 70s.
The parent groups would play song lyrics backwards and hear threatening messages.
The effects of backmasking were demanded by some groups of parents.
Random noise is what the lyrics played backward are.
If you expect to hear a threatening message in the random noise, you will most likely see an image in the clouds.
People who listened to the songs played backwards perceived the threatening messages due to top-down processing.
Top-down processing is the opposite of bottom-up processing.
We use the features of the object itself to build a complete perception instead of using our experience.
We start our perception at the bottom with the individual characteristics of the image and put them all together into our final perception.
It is an automatic process that can be hard to imagine.
Basic features of objects, such as horizontal and vertical lines, curves, motion, and so on, can be seen by feature detectors in the visual cortex.
These basic characteristics are used to build the picture from the bottom up.
We use both bottom-up and top-down processing when we see the world.
Bottom-up processing takes longer but is more accurate than top-down processing.
There are too many rules to cover in this book.
Some of the basic rules are important for the AP psychology exam.
The figure-ground relationship is one of the first perceptual decisions we must make.
There are several optical illusions that play with this rule.
The principles that govern how we perceive groups of objects were described by a group of researchers.
The psychologists said that we normally see images as groups.
They thought the process was inevitable.
There are a number of factors that influence how we group objects.
Our changing angle of vision, variations in light, and so on, causes objects to change from moment to moment.
Our ability to maintain a constant perception of an object is called constancy.
There are different types of constancy.
Our ability to gauge motion is another aspect of perception.
Our brains can detect how fast images move across our eyes, and they can also take into account our own movement.
Our brains perceive objects to be moving when they are not.
The stroboscopic effect is used in movies and flip books.
A series of still pictures presented at a certain speed will appear to be moving.
The phi phenomenon is an example of a movie marquee with holiday lights.
A series of lightbulbs are turned on and off at the same time.
The autokinetic effect is a third example.
People will report seeing a spot of light projected onto a wall of a dark room if they are asked to stare at it.
One of the most important parts of visual perception is depth.
Without depth perception, we wouldn't be able to differentiate between what is near and what is far.
The limitation could be dangerous.
The visual cliff experiment was used to determine when human infants can perceive depth.
An infant is placed on one side of a table that looks like a cliff.
The infant cannot possibly fall because the glass extends across the entire table.
An infant that is old enough to crawl won't crawl across the cliff because of their depth perception.
Experiments show that depth perception develops when we are three months old.
The monocular and binocular cues that we use to perceive depth are divided into two categories.
You have learned monocular depth cues if you have taken a drawing class.
Artists use the cues to imply depth in their drawings.
Linear perspective is one of the most common cues.
If you wanted to draw a railroad track that runs away from the viewer off into the distance, most likely you would start by drawing two lines that intersect at the top of your paper.
You could use the relative size cue if you added a drawing of the train.
The boxcars are larger than the engine in the distance.
A water tower blocking our view of part of the train would be seen as closer to us due to the interposition cue, objects that block the view to other objects must be closer to us.
If the train ran through a desert landscape, you could draw the rocks closest to the viewer in detail, while the landscape off in the distance would not be as detailed.
We know that we can see details in texture close to us, but not far away.
Your art teacher might teach you how to use shadow in your picture.
By shading part of your picture, you can say where the light source is and how deep it is.
The ability to perceive depth is due to the fact that we see the world with two eyes.
The first binocular cue-- binocular disparity-- is demonstrated by the finger trick you read about.
Our eyes look at an object from a different angle.
The brain has two images.
The closer the object is, the more disparity there will be between the images coming from each eye.
convergence is the other binocular cue.
As an object gets closer to our face, our eyes must move towards each other to keep focused on the object.
The brain gets feedback from the muscles controlling eye movement and knows that the closer the eyes are, the closer the object is.
The effect of culture on perception is being investigated by psychologists.
Some of the perceptual rules psychologists thought were innate are actually learned.
Cultures that don't use monocular depth cues in their art don't see the depth in pictures.
Some optical illusions are seen differently by people from different cultures.
There is a representation of the Muller-Lyer illusion.
Even though both lines are the same length, Line A should look longer.
The Muller-Lyer illusion is not usually used by people who come from noncarpentered cultures.
Some basic perceptual sets are learned from our culture.
If you've reviewed the senses and how the brain changes these sensations into perceptions, you can interpret the term extrasensory perception in a more specific way than most people can.
ESP claims are not accepted by psychologists because they don't find reliable evidence that we can perceive sensations other than through our sight, smell, hearing, taste, and balance systems.
Double-blind studies are used by researchers to find other explanations for ESP claims.
ESP claims can be better explained by deception, magic tricks or coincidence.
Five suggested answers or completions are followed by each of the questions or incomplete statements.
Pick the one that is the best.
In a perception research lab, you are asked to describe the shape of the top of a box as the box is slowly rotating.
You are shown a picture of your grandfather's face, but his eyes and mouth are not visible.