The processes that enable humans and other animals to sense and perceive the world around them are fundamental to psychology.
We will discuss the sensory, perceptive, and cognitive systems that allow us to do that.
Parapsychology is a pseudoscience that empirical research has largely discredited.
The process of receiving information from the environment is called sensation.
Vision, hearing, smell, touch, and taste are the five classic examples of sensation, but we also have other senses, such as the awareness of our bodies in space and our sense of balance.
The reception and transformation of incoming sensory information can be accomplished by each sense.
The sense organs receive information and pass it along for further processing.
The senses transform information from outside the nervous system into neural activity.
The stimuli that the senses detect are translated into neural activity.
The process of changing incoming stimuli to neural activity is called transduction.
Transduction begins in the sensory organs.
Neural activity is sent to the brain from the physical properties of stimuli.
The brain's thalamus does its own processing before sending the data to the cerebral cortex.
Psychophysics is a branch of psychology that studies the connection between physical stimuli and sensations.
The absolute threshold is the lowest amount of energy stimuli that an individual can detect at least 50 percent of the time.
A threshold is the point at which a sound or touch can be detected by your senses.
The justnoticeable difference is the amount of physical change required in a stimulus in order for the senses to detect a change.
Weber's law states that the size of the JND varies with the strength of the original stimuli.
Imagine that you are closing your eyes and holding a two-pound weight in your hand, and then your friend puts a one-pound weight on top of it.
You would feel the extra weight.
It is less likely that you would notice the extra pound with larger starting weights.
Weber's law shows that our psychological experience of differences in sensation is relative, requiring changes of large enough size for us to notice.
If the JND was 10%, you wouldn't notice the addition of a one-pound weight to a ten-pound one, but you would notice the addition of a twenty-pound weight.
signal-detection theory is an alternative model of how individuals respond to stimuli.
We don't encounter stimuli in isolation, but instead find ourselves in environments with many competing stimuli, so reaching the absolute threshold might not be enough for a particular stimuli to be seen.
Our brains have to process sensory information to discern between noise and signal.
There is a cognitive component to sensation, which explains why the same stimuli might be seen in different situations.
Our environments and mental states can affect our responses to stimuli.
The eye is the sensory organ that gives vision.
The eye is made up of several different parts.
The eye's outer protective layer is called the cornea.
Light waves enter the eye through the transparent structure of the cornea.
Light waves are needed for image focusing.
A popular type of laser eye surgery involves changing the cornea to allow for better bending of light into the eye.
The iris is a piece of muscle that gives the eye its color and helps to adjust the amount of light that enters.
Light enters the eye through a small opening in the iris.
The iris increases the amount of light by dilating the pupil, or reduces the amount by making it smaller.
Behind the eye is a transparent structure that bends light to reach the retina.
Intraocular fluid is found between the lens and the cornea.
The lens works by changing shape to adjust the focus for different distances.
Light could not be "accommodated" if the lens was damaged.
The sclera is the white part of the eye.
Blood vessels in the sclera supply the eye with vitamins and minerals.
Most of the eye's volume is made up of a clear fluid called the vitreous humour.
The back of the eye is called the retina.
The structure has a large network of specialized neurons that convert light into neural activity.
The two main types are rods and cones.
Rods are very sensitive to light.
The rods are essential for seeing in dim conditions.
The cones are not as sensitive to light as the rods.
There are cones in the center of the eye.
One of the most important components of visual acuity is the ability to see details.
The visual information is sent to the brain through the eye.
The visual data is transferred from the rods and cones to the bipolar cells on the surface of the retina, which process the data and then activated another network of cells called ganglion cells.
A bundle of fibers that send visual data to the brain come from the axons of the ganglion cells.
The blind spot is where the nerve exits the eye.
You can't see anything at the blind spot because there aren't any photoreceptors present and other parts of visual processing fill in the gap.
The brain has a thalamus.
The back of the brain is where the visual cortex is located.
There are cells in the visual cortex that respond to certain features of an object.
The visual cortex is where sight is produced.
Light waves are associated with three primary colors: blue, red, and green.
According to the three-color theory, the retina has three color receptors, one for each of the primary colors.
The perception of a specific color is created by the pattern of stimulation.
The Young-Helmholtz theory was developed in the 1800s and is also known as the trichromatic theory.
Some people are in fact having a fourth color receptor.
This variation only affects a small portion of the world population.
After the introduction of the trichomatic theory, a researcher named Ewald Hering wondered why people with missing color receptors could still see yellow.
The Young-Helmholtz theory did not fully account for color vision.
The opponent-process theory holds that there are opposing visual processes that allow for color vision.
Light enters our visual system with three opposing colors: white-black, red-green, and yellow-blue.
The thalamus and the retina have either turned on or off.
Some cells are turned on by green and off by red, while others are turned off by green.
After staring at a blue object, you can see a yellow afterimage for a few seconds.
These theories may be compatible.
Color vision deficiency, also known as color blindness, is one of the most common deficiencies in vision and is the most frequently tested on the AP psychology exam.
Individuals are unable to distinguish between red and green and yellow and blue in dichromatic color blindness.
Those with colorblindness can only see in shades of gray.
The cause of color blindness is usually a genetic condition.
Men are more likely to be color blind than women because of the genes on the X chromosome.
Men have only one copy of the X chromosomes, so if they have a deficient copy of a color vision gene, they don't have the potential for a functional back-up, as women do with their two X chromosomes.
The function of hearing is to convert acoustic energy into sound.
This is accomplished by passing sound waves through the ears until they reach specialized cells that transform the waves into neural impulses, which your brain interprets.
The external part of the ear is called the pinna.
The pinna is 2.5 centimeters in length and is composed of fat and cartilage.
It's purpose is to focus the sound waves towards the eardrum.
The tympanic membrane vibrates in response to sound waves.
After the sound waves cause the tympanic membrane to vibrate, they are carried into the middle ear via three small bones.
The three smallest bones in the human body are used to move sound through the middle ear and into the inner ear.
The sounds go into the inner ear through the oval window.
The cochlea is a snail-shell-shaped structure.
The basilar membrane floats in the cochlea's fluid.
The stapes cause waves to flow through the fluid by pressing against it.
The waves cause the basilar to vibrate.
The basilar membrane is stimulated by the vibrations.
The patterns of stimulation are transmitted from the basilar to the temporal cortex on both sides of the brain.
The capacity to differentiate between pitches is explained by a number of theories.
According to place theory, there are distinct locations on the cochlea.
The temporal theory maintains that pitch is a function of the frequencies at which specialized neurons in the cochlea fire are located.
The volley theory is a supplement to the temporal theory, which states that higher frequencies (ones that exceed the rate at which action potentials can fire) are encoded through the firing of multiple neurons out of phase, that combine to produce a higher rate of firing than a single neuron alone.
The perception of pitch at different frequencies may be accounted for by all of these theories.
The hair cells in the inner ear bend and move as stimuli enter.
Hearing loss is caused by damage to the hair cells.
A malfunctioning auditory nerve is one of the reasons for hearing loss.
Birth defects, medical conditions, or trauma can damage the cochlea and lead to deafness.
Scientists have created an electronic device to help people with deafness.
Cochlear implants can send sound information to the brain.
Hearing loss can be caused by structural damage to the eardrum.
The ear can no longer vibrate in response to sound waves if the eardrum is damaged.
Hearing loss can be caused by exposure to high-intensity sounds at a close range when listening to loud music through headphones.
Chemical senses are similar to mechanical senses in that they arise from the interaction of specific chemical compounds and receptors.
The sense of taste is used to detect chemicals that come into contact with the tongue.
Airborne compounds that come into contact with your nose can be detected with the sense of smell.
gustation and olfaction work very closely together, as you probably know from the wide array of flavors and scents you experience while eating.
Gustation operates in a certain way.
The taste buds in the mouth detect chemicals when they enter.
We can only detect a few basic types of taste sensations, including salty, sweet, bitter, and sour.
A fifth taste sensation called the "umami" means "delicious" in Japanese and is related to what people experience as a "savory" taste.
When the taste buds are stimulated, they send messages to the brain.
Olfaction has a similar set of processes.
As airborne odors pass through your nose, odoriferous compounds enter your body and bind to olfactory cells.
The olfactory nerve is made of a bundle of olfactory neurons.
The chemical messages travel to the brain's olfactory bulb, which processes them before sending them to the brain's amygdala.
The amygdala is a structure associated with emotions and memory formation.
It helps to explain why memories and strong feelings can be triggered by smelling a distinctive odor.
The skin is the largest organ in the body.
The signals collected by the skin are used to send messages to the brain.
The location of the receptors tells your brain where the sensation is occurring, while the frequencies of signals tell you the intensity of the stimulation.
You pull your hand away when you touch a hot stove because of the rapid firing of neurons.
The sense of touch is just one of the other senses.
The sense of body position is referred to as proprioception.
The vestibular sense helps you maintain your balance.
The inner ear has structures that help the vestibular sense.
The motion of fluid in these canals is converted into signals that are sent to the cerebellum, which helps to coordinate movement and balance.
The feeling of pain may be caused by the increase in the intensity of a tactile sensation.
Pain causes you to withdraw and seek a safe place to recuperate.
Nociceptors are located at the ends of nerves that extend from the spine to the skin.
When a pain signal is detected by these nociceptors, it travels to the spine and then to the brain.
Different stimuli, such as pressure, temperature, or caustic chemicals, can cause different types of pain in the nervous system.
There are millions of tiny nerve fibers that conduct pain signals and large fibers that control other sensory signals in the spine.
The tiny fibers that fire when your sensory organs detect pain travel to the brain.
The gate can be closed by the large fibers.
The gate-control theory is related to this.
Gate-control theory can explain how people experience pain.
The gate opens if the pain signal is strong.
The gate doesn't open for a small pain, and you don't even see it.
The gate-control theory states that the body's natural endorphins work by closing the gate.
The brain doesn't perceive the pain because the pain messages are blocked by the spine.
The process of perception integrates the sensations from your environment and gives them meaning.
When you are in a busy environment, such as your school's hallway, your perceptual abilities prioritize certain sounds, objects, or other parts of the environment.
The features you emphasize are called figures.
Maybe you hear the voice of your favorite teacher over all the other voices, or maybe you spot your best friend in a crowd.
The less important part of the environment is called the ground.
The brain determines what is figure and what is ground.
A number of factors, including an object's size, shape, color, motion, edges, and sound, help you to make such determinations in conjunction with the input from other parts of the brain.
Humans make perceptual determinations by grouping certain stimuli together.
There are several principles that describe how people organize their perception of wholes.
The following table summarizes the Gestalt principles of proximity, similarity, continuity, and closure.
The ability to see the world in three dimensions is called depth perception.
You can see depth even though you receive two-dimensional images.
Environmental cues include height, clarity, light and shadow, and relative positioning of objects.
B binocular cues aid in depth perception.
The two most important binocular signals are convergence and disparity.
The way in which the eyes must converge to see objects that are closer is referred to as convergence.
The amount of rotation gives the brain an idea of how close the object is.
Stereopsis refers to the difference between images received on each retina due to the different location of each eye.
The closer the object is, the larger the disparity in images.
Your brain is able to see motion in a series of different images.
Stroboscopic motion is what this is called.
One way to experience stroboscopic motion is by watching movies and television shows, which are really just rapid slide shows of static images.
The images themselves are moving because they succeed one another so quickly.
There are two ways in which perceptual processing can occur.
In bottom-up processing, incoming data from the environment is transmitted to the brain, where it is processed, organized, and interpreted.
The responses are integrated into a complete perception by other parts of the brain.
Bottom-up processing begins with the details and progresses to a complex perceptual whole.
In contrast to bottom-up processing, top-down processing begins with organized wholes, such as memories, expectations, and preconceived beliefs, and uses them to fill in the details.
Top-down processing can allow us to make more sense of what we see, but it can also cause us to distort what we see.
This can be seen in the discussion of perceptual constancy.
Information about our environment is provided by top-down and bottom-up processing.
Top-down processing allows us to make more sense of the overarching experience, while bottom-up processing allows us to have accurate representations of the small details.
The perceptual wholes that we experience every day are created by these processes.
Perceptual constancy is the ability to see objects the same as always.
Regardless of the size of the images, an object's size is perceived as the same.
As the brain sees the distance of an object, it uses top-down processing to adjust the perception of its size so that it stays the same.
If you see your friend at the other end of the hallway walking towards you, you can see that he or she is the same size.
The susceptibility to optical illusions is caused by the top-down processes that create perceptual constancy.
Even if the ambient lighting changes and causes alterations to the images your eyes receive, you will still perceive the color and brightness of the object to be constant.
Your perceptual system compares the brightness of surrounding images.
The same wavelength and intensity of light can seem to be different in different contexts.
The figure below shows an example of this.
The middle of the figure has a consistent shade of gray throughout, but is lighter on the left and darker on the right due to the background.
A person's experience plays a significant role in how he or she sees the world.
Our previous sensory experiences or lack of previous experience affect nearly all of our perceptual capabilities.
Culture is one of the greatest influences on your experience.
Culture can affect the way in which you see the world.
The Muller-Lyer illusion is one of the most famous optical illusions.
Two line segments are capped on both sides with arrows that point in opposite directions.
When looking at the illusion, it may appear that the bottom line is longer.
Both lines are the same size, as can be seen in the comparison image below the illusion.
Not everyone sees this illusion the same way.
Some people from Africa, India, East Asia, and Oceania don't see a difference in length.
Individuals from Western cultures tend to fall for the illusion at a higher rate than individuals from other cultures.
People from parts of Africa tend to see the same lengths of lines and are confused by the idea that someone else might see them differently.
The way we see the world can be changed by what we learn growing up in a particular culture.
The focus of attention is perception.
You know you can improve your understanding of material by concentrating on it while avoiding distraction if you study regularly.
You know that studying takes effort, just like all other instances of paying attention.
You know that you can only pay attention to the same thing for so long without tiring.
If you've been studying for a long time, you know that your attention is limited.
Try to take short breaks instead of studying for hours and hours.
The period of rest will make studying more effective when you return to the material.
While ignoring all else, you can concentrate on a particular information in your environment.
When you study, you use your attention to focus on the material in front of you and ignore other people talking, sounds from a television, or incoming social media messages.
Inattentional blindness is the failure to notice a particular stimuli when usingselective attention.
The cocktail party effect is related to attention.
The cocktail party effect is when you can ignore the other talkers while isolating your friend's voice.
When people are at a party, they tend to ignore background noise, but perk up and pay attention when someone says their name.
The sensory and perceptual processes discussed in this chapter were once considered mysteries, but scientific research has revealed much about how they actually work.
People still report strange perceptual phenomena.
The study of these "paranormal" phenomena is sometimes referred to as parapsychology, but it has yielded few, if any, results.
According to surveys, nearly half of Americans think there are people with ESP.
If a person had the power of ESP, he or she would be able to see without the help of the senses.
There are three different types of ESP: precognition, clairvoyance, and telepathy.
ESP is not the only phenomenon studied in the "field" of parapsychology, there are others, such as astrological prediction, psychic healing, communicating with the dead, out-of-body experiences, and psychokinesis, the ability to move objects directly with the mind.
ESP has been discredited in hundreds of experiments.
More research will likely be conducted in the future, though it is questionable whether it will ever convince a true believer.
The Rapid Review section contains a list of contributors to sensation and perception research.
If you want to practice for an exam on this topic, go to Rapid Review and Practice.
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