Chapter 4: Sensing and Perceiving our World

Smell (Olfaction)

1. A small area high in the lining of the nasal cavity contains the Olfactory Sensory Neurons which are similar to the hair cells in the inner ear. The Cila converts the chemical information in odor molecules into neural impulses. 2. When chemicals come in contact with the Cila, Transduction occurs, and the Olfactory Message travels to the Olfactory Bulb in the Forebrain. The Olfactory bulb sends information either directly to the smell processing areas in the Cortex or indirectly to the Corex by way of the Thalamus. 3. The primary Olfactory Cortex resides in the Temporal Lobe, The secondary Olfactory Cortex is in the Frontal Lobe near the eyes. Some fibers from the Olfactory Bulb go directly to the Amygdala, which sends smell information to the Hypothalmus, Thalamus, and Frontal Cortex. The Amygdala plays a key role in emotional responses and connects to memory areas such as the Hippocampus. These connections may explain why smells can instantly evoke emotional memory.

Difference Threshold

1. Absolute Thresholds holds involve perceiving or not perceiving a stimulus. But what about perceiving when a stimulus changes? Once we already perceive a stimulus, how much does it have to change before we notice that change? this threshold is known as the difference threshold. Difference Thresholds are relative thresholds and are also referred to as just noticeable differences (JND) because they involve the smallest difference that is noticeable. 2. For example, being able to perceive slight differences is essential to a piano tuner, who has to be able to distinguish the slightest change in pitch to tune the instrument. Importantly, people differ in their JND sensitivity. For Instance, the Piano tuner will no doubt recognize differences in pitch that most people will not.

Information processing from sight to the eye

1. After Transduction at the Photoreceptor layer, visual information is processed by different layers of cells in the Retina. One of these layers is made up of ganglion cells. The Axons which make up the Optic Nerve. 2. The Optic Nerve transmits signals from the eye is called the blind spot of the Retina because this location has no receptor cells and therefore nothing is seen.

Gestalt Notion figure and ground

1. Another Key Gestalt Notion concerns how we separate things into figure and ground, where the figure is the thing that stands in front of a somewhat unformed background. Gestalt Psychologists pointed out that we readily separate a figure from it's background. Gestalt Psychologists pointed out that we readily separated a figure it's background in order to perceive it. 2. Perhaps the most famous example of figure ground effects is the face-vase figure, It is impossible to see both the vase and the faces at the same moment.

The Ear

1. As the structures on the sides of our head, our ears have little to do with hearing itself. These external structures, called Pinnae, collect, and Funnel sounds into the passage called the Auditory Canal. 2. Once inside this canal, sound vibrations travel to the eardrum, or tympanic membrane makes up the outer ear. The sound waves on the Tympanic Membrane set into motion the bones of the middle ear, the hammer, evil, and stirrup. These bones do more than just vibrate, However, they amplify the waves so that they have more than 20 times the energy they had entering the ear. The hammer hits the anvil, and the evil moves the stirrup. The Vibration of the stirrup in turn sets into motion a series of important changes in the inner ear.

Binocular Depth cues

1. Binocular Depth Cues rely on input from both eyes, one key binocular cue to depth comes from the fact that the eyes are separated by a few inches, so the images from each eye provide slightly different viewpoints. The difference in these Retinal Images, or Binocular Disparity, plays a key role in our ability to perceive depth. To see how this works, hold a finger out in the front of you, close one eye, open it, and then close the other eye. You will see how the image shifts slightly to one side, depending on which eye is closed and which eye is opened. The Brain integrates these two slightly different two-Dimensional Images into a single three-dimensional image.

Single Section Theory

1. Classic research from the 1960s reported that, under ideal laboratory conditions, an average person on a very clear night can detect a single candle from 30 miles away or can distinguish 2 gallons of water with 1 teaspoon of sugar as being different from 2 gallons of pure water. 2. Detecting sensation is a matter not only of the intensity of the stimulus but also of the person's decision making process in a particular context. 3. Single Section Theory attempts to separate " signal" from " Noise" and takes into account both stimulus intensity and the decision making processes people use in decking a stimulus.

Perceiving Color

1. Color is not a property of objects It is a property of us. Our Perception of color depends on our Photoreceptors, our brains, and the physical characteristics of the stimulus we look at. Color Perception is partly determined by wavelength measured in billionths of a meter or Nanometers (nm) which most of us perceive as read. The light that we perceive as green is at 550 nm. 2. Humans and other primates-Humans included have three kinds of cones: those that are sensitive to red, green, or to blue wavelengths of light. Humans, therefore, are Trichromatic ( Sensitive to three colors) 3. A million colors we see are simply combinations of different intensity of these three wavelengths, mammals other than primates are sensitive to only two pigments, they are Dichromatic Sensitive only to blue and green wavelengths. A few humans approximately 2% and always women are Tetrachromatic. Tetrachromic people see 100 million colors compared to the 1 million colors that most people see, and because they have moncones, their vision is also sharper than most.

Cones

1. Cones are responsible for color vision and are most functional in conditions of bright light, they act much more quickly than rods on exposure to light, cones reach maximum effectiveness in about 5 minutes Because the chemicals involved in their function replenish quickly. 2. The Fovea is a spot on the back of the Retina contains the highest concentration of cones in the Retina. We see images with the greatest clarity when they are focused on the Fovea. So Visual Acuity or our ability to see clearly depends on our cones. Animals that have the most cones have the best acuity.

Perceiving Motion

1. Features Dectors play a role in how we preserve moment and form. We perceive movement when an image moves across the Retina. Simple and Complex Cells respond to either the orientation or the direction of moving images. Sometimes these moving images truly reflect movement in the world around us. 2. As we view any scene, at least two factors contribute to how we perceive movement. The background against which an object moves and the size of the object.

Gestalt law of proximity

1. Gestalt Tendency group objects together is known as a similarity. According to the Gestalt Law of Continuity, we see points online in such a way that they follow a continuous path. 2. The Gestalt law of proximity says that we tend to ground together objects that are near one another.

Pain Perception

1. How do we sense and perceive pain? Damage to the skin is only one kind of pain. Other forms include organ tissue and Nerve Damage, as well as joint inflammation. 2. Pain from the skin and or tissue damage or injury is called Nociceptive Pain. The skin has pain receptors that are sensitive to heat, cold, chemical irritation, and pressure. All these pain receptors are kinds of nociceptive Pain. Getting Frostbite, suffering from chemical burns, and hitting your thumb with a hammer all hurt because these events stimulate Nociceptors in the skin. 3. The Nociceptors send signals to the Spinal cord and then to the brain, Signaling that damage has occurred, the Brain can then initiate an appropriate response, such as pulling your hand away from a hot burner, You can now see why not experiencing pain would be so dangerous.

Perceiving Patterns and Wholes

1. How is that we recognize a set of marks on a page as a letter or a shape's rather than just a bunch of marking? The Gestalt Psychologists recognized that often we perceive wholes as more than merely the sum of their parts. Gestalt is German word that means "Form" pattern or shape. German researchers Max Wertheimer. Kurt Koffka, and Wolfgang Kohler studied and visual perception in the early 20th century and described a set of principles or laws by which people organize elements of figures or sciences into whole objects. The Major Gestalt Laws of Visual organization are similarity, continuity, proximity, closure, and figure-ground.

What are the different kinds of tastes?

1. Humans distinguish among five basic qualities: Bitter, Sweet, Salty, Sour, and Savory, Researchers once thought that Receptors for the different tastes resided only in certain regions of the tongue, But we know that these taste receptors cells are distributed in many regions. 2. Just as there cortical regions for seeing, hearing, touching, and smelling, there is one for tasting, It is known as the gustatory cortex and is located in the Insula Region of the Frontal Lobe right where the Temporal and Parietal Lobes Intersect.

Sensory Adaptation

1. Imagine if you were constantly aware of the sensations that bombard your sense organs such as the sound of the air conditioner and traffic, the sight of the chair you're sitting on, and the rug on the floor. The smells in the air and the feel of your clothing against your skin if you were constantly sensing all this, you would suffer from sensory overload. 2. Our Sensitivity diminishes when we have constant stimulation, a process known as sensory adaptation. Sensory Adaptation ensures that we notice changes in stimulation more than stimulation itself.

Mechanoreceptors and Touch Part 1

1. Imagine that your eyes are closed and someone puts an object in your left hand. For a minute, You feel it's weight, shape, hardness, and temperature. Then the person puts something in your right hand, you conclude, with eyes still shut, that the first a screwdriver and the second is a pen. How are you able to do this? 2. The Top layers of skin have receptor cells that are sensitive to different tactile qualities some to shape, some to grooves, some to vibrations, and movements. These Receptor Cells are known as Mechanoreceptors and they are like the Photoreceptors in the eye and the Hair Cells in the ear. There are four kinds of Mechanoreceptors, each kind has a unique profile of sensitivity. Some of the Mechanoreceptors are slow to change, and others are fast with variations in tactile stimulation. Photoreceptors in the eye mechanoreceptors mark only the beginning of the journey from sensation to perception.

Controlling Pain

1. In addition to thought and feel that control the experience of pain, our bodies have natural painkillers called endorphins. When we are hurt, our bodies respond by releasing these substances. Endorphins work by stimulating the release of Neurotransmitters that interfere with pain messages in the Spinal Cord and Brain. 2. Endorphins release may explain why some people such as soldiers and car accident victims, report no immediate sensations of pain after a horrible injury. Only Hours afterward or maybe the next day while in a hospital does the pain began. Endorphins also play a role in acupuncture-based pain relief. 3. If thoughts, feelings, and Endorphins are not enough to control pain, there are drug treatments. For small aches and pains, many people take aspirin, acetaminophen, ibuprofen, or other similar drugs. Generally, these drugs work to control inflammation. For more severe pain, doctors may prescribe opioids, Morphine, Heroin, Oxycodone, and Hydrocodone are all opioids. All but Herion are commonly prescribed for pain relief. They deaden or lessen pain by blocking neural activity involved in pain perception. There is a high risk of Dependency on Opioids, so their use must be carefully monitored.

nearsighted vs farsighted

1. In people with normal vision, the lens projects the image to hit just on the Retina. In people who are nearsighted ( Myopic) the image focuses slightly in front, of the Retina. Nearsighted people can see close objects clearly. But distant objects are fuzzy. In people who are farsighted (Hyperopic) the image focused behind the Retina, They can see distant objects clearly, But close objects clearly, But close objects are Fuzzy, As people age, the lens become less flexible, and it is more likely that the visual image will focus behind the Retina, This is an age-related form of farsightedness.

Signal Detection Research

1. In signal detection research, a low-intensity stimulus is presented on some occasions but not presented on other occasions. Instead of having a 50% detection line, which is a threshold. 2. In a single section study, the participant's response creates a profile of hits, misses, false alarms, and correct rejections, a person's threshold is assumed to be constant ( For example, the light intensity of 180) But in signal detection, It is assumed that a person's absolute threshold fluctuates, sometimes being more sensitive and other times being less sensitive, depending on the coast of failing to detect the stimulus.

Perception

1. Is the act of organizing and interpreting sensory experience. It is how our psychological world represents our physical world. You read and make sense of the marks on the page because you spent years learning to speak and read English, and your brain transforms the raw sensory experience into meaningful concepts. 2. We can have different experiences in the real world because individuals can experience the same physical object in different ways. The Brain organizes and interprets sensory experience to give it meaning. Before the brain can create meaning from sensory information, our sense organs transform physical stimuli from the outer world to a form that the Brain can use Action Potentials.

Sensation

1. Is the stimulation of our sense organs by the outer world. Eyes are sensitive to light waves, ears to sound waves, skin to touch and pressure tongues.

How people's absolute thresholds differ

1. It is important to point out, however, that people differ in their absolute thresholds with some people more sensitive than others, for Instance, Introverts compared to extroverts are more sensitive to most sensory stimulation, including sound, smells, light, and pain. Similarly, depression is related to less sensitivity to pain and cold perception.

Vision and the eye

1. Light enters the eye at the Cornea a clear, hard covering that protects the Lens. It then passes through liquid until it reaches a hole called the Pupil. Light enters the interior of the eye through the pupil. 2. The colored part of the eye the Iris adjusts the pupil to control the amounts of light entering. The light then passes through the lens which bends the light rays. 3. Through a process known as accommodation, muscles, around the lens alter its shape to adjust to viewing objects at different distances and to allow the lens to focus light on the Retina. 4. Finally, the Retina is a thin layer of nerve tissue that lines the back of the eye, whose main function is to convert light energy into neural energy. The light that hits the retina through several cell layers before processing begins. Note how the image hits the Retina upside down. The Brain reorients the inverted image so that our world is right-side up. The deepest layer of cells, where the processing of light energy begins, is made up of Photoreceptors

Distance Cues ( Horizon)

1. Makes objects look bigger than they are. More Famously, the moon illusion occurs when the moon illusion occurs when the moon is closer to the horizon.

How does your Brain help you feel pain?

1. Many brain structures are involved in the perception of skin damage alone. A partial list of Brain Structures activated by skin based pain includes the Thalamus, Hypothalamus, Limbic System, Insula, and Anterior cingulate cortex. 2. Some of the same brain regions and Neurochemicals activated when we experience physical pain are also activated during emotional pain, especially when we are rejected by others or see others receive shocks. 3. Interestingly, those who are born without the ability to experience pain also do not experience whether it is physical or emotional.

Vision

1. Most mammals rely on smell over all other senses, but Humans are predominately visual creatures. We rely so much on our sense of sight that we often ignore other types of information. 2. Why is Vision so important? In terms of evolution, being able to see helps us know where we are, what other people might want from us, and whether there is danger nearby. 3. As Hunter-gathers, our vision is critical for locating prey and avoiding danger, as well as for finding foods we can eat, we also rely on hearing, The Second most important sense, and smell, But vison is king and it starts with the eye.

Pain

1. Pain is a complex emotional and Sensory Experience associated with actual or potential tissue damage. It is usually very unpleasant, but people vary widely in their experiences of pain, but people vault widely in their experiences of pain, what they think is painful, and whether they might even enjoy pain, some people feel no pain during great injury and others feel pain when no tissue damage is present.

Shape constancy

1. People know the shapes of common things, Just as they know their sizes, The Brains uses this knowledge to override changing retinal images that might make the world very confusing. When we see a door that is closed, It looks like a rectangle ( and this is what the 2-D image on our Retina looks like) A door that is partially open looks like a trapezoid. Still we would not think that the door has suddenly changed shape. The Brain corrects doors retain their shape when they change positions. The Brain corrects our perception based on our previous knowledge that doors retain their shape when they change position.,

Rods

1. Rods play a key role in night vision, as they are most responsive to dark-and-light contrast. They work well at low illumination, we have all experienced rods in action, consider what happens when someone turns out the lights. 2. At first, everything is completely dark. Then, with a bit of time, we begin to see shapes and forms. Although we cannot really see colors, the process of adjustment to seeing in the dark, known as Dark Adaptation, can take up to 30 minutes. and reflects the rods at work. Rods are very sensitive, However, and sudden exposure to light can quickly cancel out their effectiveness.

Chemical Sense: Smell and Taste

1. Smell and Taste are chemical senses Because they respond to contact with Molecules from objects we encounter in the world. Unlike receptors for other senses, Receptors for Chemical Molecules are regularly replaced, because they are constantly exposed not only to the chemicals in food but also to dirt and bacteria that can impair function. Smell and Taste receptors are replaced every few weeks.

Psycho Physics

1. Some of the earliest experiments in Psychology were in the field of Psycho Physics, the study of how people Psychologically perceive Physical Stimuli such as light, sound waves, and touch.

Taste

1. Taste evolved as a way of telling animals whether something was edible or not and in particular whether it was likely to be energy-rich (sweet) or noxious (Bitter). A close look at the Human Tongue reveals all kinds of ridges and bumps. These texture structures, called Papillae, contain about 10,000 taste buds. 2. Dozens of taste Receptors cells on each bud process taste information. Human experience taste results primarily from the stimulation of taste buds throughout the tongue, When chemicals from food or liquid come in contact with the tips of these taste buds, a chain of events unfold leading to the experience of taste.

The Inner Ear

1. The Inner Ear includes the cochleae and semicircular canals. The Semicircular canal plays a key role in maintaining a sense of balance. As the stirrup vibrates, it moves a membrane that covers the inner ear, alley the oval window. 2. The Vibrations on the Oval window send movement through the fluid-filled cavity of the Cochlea, a bony tube, curled like a snail's shell, and filled with fluid. The Basilar membrane runs through the Cochlea, within the basilar membrane of the cochlea are haircells. which are the sensory receptors for sound, Just as the photoreceptors are for vision. 3. As the vibrations move through the Cochlear fluid, the basilar membrane vibrates, making the hair cells bend. As they bend, they transduce the sound vibrators into electrical impulses. Which may generate an action potential in the Auditory Nerve and the louder the sound we perceive. 4. If the hair cells in the inner ear become damaged, as can happen when a person is exposed to very loud noises once or moderately loud noises over long periods of time, the person can suffer irreparable hearing loss.

Visual Information to the Brain Part 2

1. The Thalamus serves as a Relay Station for most of the major sense inputs to the Brain, taking information from the sense organs and sending it to the relevant area of the cerebral cortex for processing, occurs there. 2. A cluster of the Neuron cells bodies in the Thalamus forms the Lateral Geniculate Nucleus (LGN) visual information creates a point-by-point representation of the tissue of the LGN. Patterns of neural firing that correspond to the shape projected on a specific region of the Retina affect a similar layer of cells in the LGN, so the Retina and the LGN represent visual information in similar ways. 3. Fibers from the LGN in the Thalamus then travel to the visual cortex in the occipital lobes. Neurons in their visual cortex analyze the Retinal Image in terms of its various patterns, contrasts, lines, and aspects of this analysis.

How does the Brain perceive Visual Stimuli

1. The eye is where we sense visual information and the brain is where we make sense of it ( Perceive Visual Information) But making sense of perceiving the neural information from the eye involves many different acts of perception: Colors, Depth, Size, and Patterns, among others. 2. Each of these perceptual processes works together to help us recognize objects in the world.

Explaining Pain

1. The gate control theory of pain proposes that the Spinal Cord regulates the experience of pain by "gating" the transmission of the pain information at the level of the spinal cord. The gate is not literally a gate but rather a competition between signals coming from different-sized axons or nerve fibers. 2. More specifically, pain signals are sent via smaller nerve fibers than non-pain signals. Experienced Pain is all about the balance and Imbalance between signals from the pain fibers (Small) relative to the non-pain Fibers ( Large) When injury to skin or tissue occurs, for instance, there is more signaling from small pain fibers than the large non-pain ones. The "gate" has opened on the hand, when there are more signals from the larger nonpain fiber pain is not experienced. The "gate" has closed. This is why small levels of pain can be blocked by rubbing one's skin or even acupuncture: the non-pain signals dominate and override or close the gate of the pain signals being sent to the brain. 3. Thoughts, Feelings, and Beliefs can affect pain sensations, which is one reason people vary so much in their perception of pain different people experiencing the same level of pain may have completely different experiences of their pain.

amplitude and frequency

1. The height or amplitude, of the sound wave determines what we perceive as loudness. The taller the wave is the louder the sound. 2. The scale for a sound's loudness in decibels (dB) starting with 0, which is the threshold for normal human hearing. The scale has no upper limit, but sounds above 150-170 dB are seldom registered anywhere. 3. The frequency of. a sound wave, or how many waves sounds pitch. Frequency is measured in units called hertz (Hz) which is how many times the wave goes per second. The higher the frequency, the higher the pitch. The range for human pitch perception is from about 20Hz to about 20,000 Hz But most people cannot hear sounds at either extreme. Sounds below 20 Hz are called subsonic and above 20,000 is called subsonic and above 20,000 are called ultrasonic. Most sounds we hear are in the range of 400 to 4,000 Hz. The Human voice generally produces sounds ranging from door to 800 Hz.

Transduction

1. The sense organs convert physical stimulate into neural impulses. This conversion of physical into neural impulses. This conversion of Physical into neural information is called Transduction. 2. When cells in the Retina change light waves to neural energy, when the hair cells in the inner ear change sound waves to neural energy, when chemicals in the air bind to receptors in the nose, when food chemicals stimulate taste buds on the tongue, and when pressure and temperature stimulate nerve cells in the skin. In Short, Transduction is when outer world becomes the Inner World.

Mechanoreceptors and Touch Part 2

1. The sensory qualities ( Shape, Size, Hardness, and Temperature) of the screwdriver and pen stimulate different kinds of mechanoreceptors in the skin, But the resulting sensory impulses must travel skin, but the resulting sensory impulses must travel to the Brin to be processed and interpreted. 2. When something touches our fingertips, forearm, or shoulder, a dedicated region of Cortex becomes active, cord, and up to the Brain. The first major structure involved in processing bodily sensations is the Thalamus, which relays the impulses to the Somatosensory Cortex in the Parietal Lobes. 3. Again, due to neuroplasticity, repeated sensory and motor tactile experience changes the amount of Cortex involved in processing a particular or movement. The general location in the Somatosensory Cortex stays the same, but the areas, of the cortex devoted to that experience or function grow. The more one body region is touched or stimulated, the more sensory or motor cortex is used to process information from the Mechanoreceptors.

Purity

1. The third property of sound waves is purity, is the complexity of the wave, Some sound waves are pretty simple, made of only one frequency. Most waves are complex that is, they contain a mixture of frequencies. A sound's purity or unique tonal quality, which we perceive as Timbre, is determined by how many frequencies are present in the wave.

Deficiencies in color vision

1. There are many types of color blindness, only about 10 people in a million that actually fail to see color at all. More commonly, color blindness refers to a weakness or deficiency in the Perception of certain colors, usually resulting from an inherited pigment deficiency in the Photoreceptors. 2. Color Blindness almost never means that a person sees the world in Black and White, But rather sees fewer colors. The most common form, often seen in men and boys due to the pattern of inheritance, occurs from a deficiency in cones sensitive to green light. People with this disorder have trouble distinguishing some shades of green from red, may see green and brown as similar, or might have difficulty distinguishing Blue and Purple. Yellow-Blue deficiencies are less common.

Apparent Motion

1. We can also be fooled into thinking something is moving when it is not. We refer to this illusion as apparent motion because our brains interpret images that move across over our Retinas as a movement. The "Moving" lights on a movie theater marquee are a rapid succession of bulbs lighting up in a row. Even though we know the lights are not moving. We still interpret this illusion as movement.a

Monocular Depth Cues

1. We derive a great deal of information about depth from the numerous monocular depth cues ( Monocular means one eye" that does not require two eyes to be effective. These cues allow people who are blind in one eye to perceive some depth.

The Bodily Senses

1. We feel things on our skin and in our organs. The largest contact of the surface area any sensory input has with our bodies is the skin, and its carefully mapped in the Somatosensory Cortex in the Parietal Lobe of the Brain. The senses based in the skin, body, or any membrane surfaces are known as the bodily senses, which include knowing where our body parts are. 2. We also sense things inside our bodies Organ Pain, levels of heart rate, depth of breathing, to name a few senses: Touch, Temperature, Pain, Posture, Motion, Balance, and interception, ( perception of body sensations)

Perceiving Size and Shape

1. We know what familiar objects look like. We also know that, when they change position or distance in relation to us, they remain the same. Nevertheless, the images on our Retinas change shape and size as objects move through shape and size as objects move through space the Brain's ability to preserve the perception of such objects in spite of the changes in Retinal Image known as Perceptual Consistency. The two types are Constancy of size and of shape.

Hearing

1. We perceive different shapes and sizes of sound waves as different sounds. Hearing is affected by three physical properties of the sound wave: Its amplitude, Frequency, and Purity.

Size Constancy

1. We see things as the same size regardless of the changing size of the image on the retina, because we know what the size of the object is. If you see your friend Jason, who is about 6 feet tall, walking away from you, The size of his image on your retina shrinks, yet you do not suddenly think, oh no, Jayson is shrinking! Your knowledge of Jayson's height and your knowledge that people maintain their height even when they move away from you prevents you from interpreting the smaller retinal image as a smaller person. Also distance cues, such as linear perspective. Indicative that the road Jayson is walking on is In the Distance, and your brain makes use of this information plus your knowledge of Jayson's size to keep his size constant in your mind.

Perceiving Depth

1. We take for granted that we see things in three dimensions and can discriminate what is never, from what is far, this is called Depth Perception, a remarkable skill, given that the image projected on the Retina is two-Dimensional, How does this work? Two major aspects of Human Visual Anatomy and processing allows for Depth Perception: Binocular and Monocular Depth Cues.

Sensing Visual Stimuli

1. What does the eye do? It bends light, converts light energy to neural energy, and sends that information to the brain for further processing. The Eye is the gateway to vision, but very little of what we experience as vision actually happens in the eye. 2. Visual Perception happens in the Brain, with input from the eye.

How does the movement and background affect how we perceive motion?

1. When an object moves across a complex background. It appears to move faster than when it moves across a simple background. 2. For example, a deer running across a field, with mountains and trees in the background objects provide references that help us note the change of position in the deer. The Human Visual system is quite sensitive to changes in the position of objects. a sensitivity that appears to decline a bit with age.

Absolute Threshold

1. When do we go from not sensing an object or event to sensing it? For example, what is the softest sound you can hear? These questions concern the Absolute Threshold, the lowest intensity level of a stimulus we can detect half of the time. 2. A common way to assess absolute thresholds is for a researched to present stimuli, such as light, of different intensities to a research participant. 3. The Intensity level that a participant can see 50% of the time is that person's Absolute Threshold for light. Imagine that six intensities, whose values are 150, 160, 170, 180, 190, and 200, are presented 10 times each of these values, a participant detects the 180 value 50% of the time time. Then 180 is this person's absolute threshold for this light stimulus.

Visual Information to the Brain Part 1

1. When visual information arrives in the Brain the Optic Nerve carries impulses to the Thalamus and, ultimately, to the visual cortex of the occipital lobes, the information from the left visual field is processed in the Brain's Right Hemisphere, and the information from the right visual field is processed in the Brain's Left Hemisphere. 2. In each eye, each half of the Retina sends out it's own Axons. Thus, each Optic Nerve has two strands. One strand contains Axons that travel from the Retina to the Thalamus and on the Visual Cortex of the same side of the Brain as the eye from which the Axons come. The other strand crosses to the opposite side of the brain in an area called the Optic Chiasm. 3. The first stop in the Brain for most of the Optic Nerve fibers is the Thalamus. If the pathways to the Thalamus are cut, visual perception is not possible. Beyond some crude ability to detect the presence of Stimulus.

convergence

A binocular cue for perceiving depth; the extent to which the eyes converge inward when looking at an object

Linear Perspective

Involves parallel lines that converge, or come together the farther away they are from the viewer. The more they can verge, the greater distance we perceive. with

Phantom limb pain

Pain also is enhanced by one's reaction to the injury, Often the emotional reaction the pain creates much suffering as the actual tissue damage.to

Cornea

The clear tissue that covers the front of the eye

dark adaptation

The process in which the eyes become more sensitive to light in low illumination.

trichromatic color theory

The theory of color vision that holds that all color perception derives from three different color receptors in the retina (red, green, and blue receptors).

Iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

bottom-up processing

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

Binocular Depth Cues

clues about distance based on the differing views of the two eyes

Atmospheric Perspective

comes from looking across a vast space into the distance in the outdoors. Anyone who has stood at the edge of the Grand Canyon has seen Atmospheric Perspective at work, We look through air and particles in the air ( More so when the air is polluted) objects farther away from the viewer which overlap those farther away. This is reliable cue to depth.

Monocular Depth Cues

cues of depth perception that are available to each eye alone

binocular cues

depth cues, such as retinal disparity, that depend on the use of two eyes

bipolar cells

eye neurons that receive information from the retinal cells and distribute information to the ganglion cells

top-down processing

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

Texture Gradient

is a monocular depth cue that causes the texture of a surface to appear more tightly packed together as the surface moves to the background. These changes in textural information help us judge depth.

Photoreceptors

rods and cones

types of photoreceptors

rods and cones

visual acuity

sharpness of vision

depth perception

the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance

Pupil

the adjustable opening in the center of the eye through which light enters

Fovea

the central focal point in the retina, around which the eye's cones cluster

Muller-Lyer Illusion

the illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

Optic Nerve

the nerve that carries neural impulses from the eye to the brain

Weber's Law

the principle that to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)

accommodation

the process by which the eye's lens changes shape to focus near or far objects on the retina

Stroop Effect

the tendency to read the words instead of saying the color of ink

Opponent-Process Theory

the theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green

Lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

Ganglion Cells

their axons form the optic nerve

Gestalt Law of Continuity

we tend to see smooth, continuous patterns rather than discontinuous ones

The Law of Closure

when space is enclosed by a group of lines, it is perceived as a complete or closed line