Sensation and Perception: A Summary of Topic 3

Sensation and Perception Sensation - A physical process: where our sense organs (like eyes, ears, skin, nose, and tongue) detect and respond to external stimuli (things from the outside world). Ex. When you touch a hot stove, your skin's nerve endings (sense organs) feel the heat. This feeling o...

Sensation and Perception Sensation - A physical process: where our sense organs (like eyes, ears, skin, nose, and tongue) detect and respond to external stimuli (things from the outside world). Ex. When you touch a hot stove, your skin's nerve endings (sense organs) feel the heat. This feeling of heat is a sensation. Perception - A psychological process: the act of organizing and interpreting sensory experience. Perception helps us understand and give meaning to our surroundings, based on past experiences, expectations, and context. Ex. If you touch a hot stove and feel the heat (sensation), perception is when your brain interprets that feeling as "hot" and "dangerous," prompting you to pull your hand away. Your perception of the world of changing sights, sounds, and other sources of sensory input depends largely on the so- called five senses: vision, hearing, smell, taste, and touch Different concepts in Sensation and perception 1. absolute threshold, 2. subliminal stimulation, 3. difference threshold, 4. signal–detection theory, 5. feature detectors 6. sensory adaptation Principles of Perception 1. Absolute Threshold - is the minimum level of stimulus intensity needed for a person to detect a stimulus 50% of the time. It's the weakest amount of a stimulus that a person can still perceive. Example: For light, the absolute threshold would be the dimmest light that someone can see in a completely dark room. If the light is any dimmer than this level, it wouldn't be detected by the person’s visual system. For hearing, the absolute threshold might be the faintest sound a person can hear, like the ticking of a watch from a certain distance in a quiet environment. 2. SUBLIMINAL STIMULATION - refers to sensory input that is below a person’s absolute threshold for conscious perception. This means the stimulus is too weak or brief for us to be aware of it. Subliminal perception - Visual stimuli can be flashed too briefly to enable us to process them. Ex. If a picture is flashed on a screen so briefly that you don't consciously see it, but it still influences your thoughts or feelings, that’s subliminal perception. Auditory stimuli - can be played at a volume too low to consciously hear or can be played backward Ex. If a message is played at a volume too low for you to consciously hear or is played backward, but still affects your behavior or attitudes, that’s an example of subliminal perception.  Subliminal stimuli refer to stimuli that are attended to by the brain but not consciously perceived, often achieved through brief presentation followed by masking procedures to prevent conscious awareness 3. DIFFERENCE THRESHOLD - also known as the just noticeable difference (JND), is the smallest amount of change in the intensity of a stimulus that a person can detect. In other words, it’s the minimal difference between two stimuli that can be noticed. Ex. Light: If you are in a room with two light bulbs, the difference threshold would be the smallest change in brightness between the two bulbs that you can perceive. If both bulbs are equally bright, you won't notice any difference. But if one bulb becomes just slightly dimmer or brighter than the other, the point at which you notice this change is the difference threshold. 4. SIGNAL - DETECTION THEORY - The view that the perception of sensory stimuli involves the interaction of physical, biological, and psychological factors People’s ability to detect stimuli such as blips on a radar screen depends not only on the intensity of the blips but also on their training (learning), motivation (desire to perceive blips), and psychological states such as fatigue or alertness Ex. Imagine you are in a noisy room waiting for a friend to arrive and knock on the door. If you are highly focused on hearing the knock, you might hear it even if it's faint, due to your heightened alertness and expectation. However, if you are distracted or not expecting the knock, you might miss it even if it's louder. Signal-detection theory helps explain why your perception can vary in these different scenarios. 5. FEATURE DETECTORS IN THE BRAIN Feature detectors neurons in the sensory cortex that fire in response to specific features of sensory information such as lines or edges of object. Ex. when looking at a face, different feature detectors respond to specific facial features like eyes, nose, and mouth, which helps the brain recognize that it's seeing a face. SENSORY ADAPTATION- The processes by which organisms become more sensitive to stimuli that are low in magnitude and less sensitive to stimuli that are constant or ongoing in magnitude Ex. Touch: When you first put on a watch or a ring, you can feel it on your skin, but after a while, you stop noticing it. This is because your skin receptors have adapted to the constant sensation of the object. Sensitization the type of sensory adaptation in which we become more sensitive to stimuli that are low in magnitude. Also called positive adaptation Ex. After spending time in a dark room, your eyes become more sensitive to low levels of light, allowing you to see better in the dark. Desensitization the type of sensory adaptation in which we become less sensitive to constant stimuli. Also called negative adaptation Ex. When you first enter a room with a loud air conditioner, it seems very noisy, but after a while, you stop noticing the sound as your ears become less sensitive to it.  Vision Humans are predominantly visual creatures. Being able to see helps us: know where we are, what other people might want from us, and whether there is danger nearby. Our eyes are literally our “windows on the world.” Because vision is our dominant sense, blindness is considered by many to be the most debilitating sensory loss  What is light? Visible light is the portion of the electromagnetic spectrum that human eyes can perceive. It ranges from wavelengths of about 400 to 700 nanometers and is responsible for the colors we see. Ex. When you look at a rainbow, you see different colors like red, orange, yellow, green, blue, indigo, and violet. These colors are created by different wavelengths of visible light being scattered and separated.  Vision and the Eye 1. Light enters the eye at the cornea (a clear, hard covering that protects the lens). 2. The amount of light that passes through the cornea is determined by the size of the opening of the muscle called the iris which is the colored part of the eye. The opening in the iris is the pupil 3.Once light passes through the iris, it encounters the lens. 4. The lens adjusts or accommodates to the image by changing its thickness. Changes in thickness permit a clear image of the object to be projected onto the retina. 5.The light that hits the retina travels through several cell layers before processing begins. The deepest layer of cells, where processing of light energy begins, is made up of photoreceptors. Two types: Rods - Photoreceptors that function in low illumination and play a key role in night vision (dark adaptation); responsive to dark and light contrast. Cones - Photoreceptors that are responsible for color vision and are most functional in conditions of bright light; Visual Acuity, or our ability to see clearly, depends on our cones. Vision and the Brain After transduction at the photoreceptor layer, visual information is processed by different layers of cells in the retina. The optic nerve transmits signals from the eye to the brain. The optic nerve exits the eye through the blind spot  Visual Acuity (sharpness of vision) 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 In people who are farsighted (hyperopic), the image focuses behind the retina. Beginning in their late 30s to the mid-40s, people’s lenses start to grow brittle, making it more difficult to accommodate to, or focus on, objects. This condition is called presbyopia, from the Greek words for “old man” and “eyes.” Presbyopia makes it difficult to perceive nearby visual stimuli  dark adaptation the process of adjusting to conditions of lower lighting by increasing the sensitivity of rods and cones Ex. When you enter a dark theater from a brightly lit environment, you initially struggle to see. After a few minutes, your eyes adjust, and you can see more clearly in the dark theater. This adjustment is your eyes undergoing dark adaptation.  Color Vision  Perceiving Color Wavelength: Determines the color or hue of light. For example, light with a wavelength of around 480 nanometers appears blue, while light with a wavelength of around 700 nanometers appears red. Value: Refers to the brightness or darkness of a color. A color with high value is lighter, while a color with low value is darker. For example, sky blue has a higher value (lighter) compared to navy blue (darker). Saturation: Indicates the intensity or purity of a color. Highly saturated colors are vivid and pure, while less saturated colors appear more muted or pastel. For instance, fire-engine red is highly saturated, making it bright and intense, whereas a pale pinkish-red has lower saturation, appearing softer and less intense.  Theories of Color Vision Trichromatic color theory - all color that we experience results from a mixing of three colors of light (red, green, and blue) Trichromatic theory does not fully explain the phenomenon of afterimages, where you see a color's complementary color after staring at a bright color for a while. For instance, if you stare at a red image and then look at a white surface, you might see a green afterimage. This phenomenon is better explained by the opponent- process theory, which posits that color perception is controlled by three pairs of color receptors (red-green, blue-yellow, black-white) that work in opposition. Opponent-process theory - suggests that color vision is made possible by three types of color receptors that work in opposing pairs. Cones are linked together in three opposing color pairs: blue/yellow, red/green, and black/white. Ex. If you stare at a bright red square for a while, the red receptors in your eyes get tired. When you then look at a white surface, the tired red receptors don’t work as well, so the green receptors (which were blocked by the red ones) become more active, and you see a green afterimage.  Colorblindness Only about 10 people in a million actually fail to see color at all (Goldstein, 2007). color blindness refers to a weakness or deficiency in the perception of certain colors. Trichromat - a person with normal color vision Monochromat- a person who is sensitive to black and white only and hence colorblind Dichromat They can discriminate only between two color red and green or blue and yellow and the colors that are derived from mixing these colors. (Partially colorblind)  Perceptual Organization Gestalt psychologists observed that people tend to naturally organize sensory information into meaningful patterns and wholes rather than just separate parts. They proposed several principles, known as the laws of perceptual organization, which describe how we group and interpret sensory information to form a cohesive perception.  Key Gestalt Laws of Perceptual Organization: 1.Law of Proximity: Objects that are close to each other are perceived as a group. 2.Law of Similarity: Items that are similar in appearance are seen as belonging together. 3.Law of Continuity: We perceive continuous lines and patterns rather than disjointed ones. 4.Law of Closure: Our minds fill in gaps to create complete, whole objects even if parts are missing. 5.Law of Figure-Ground: We tend to separate images into the main object (figure) and the background (ground).  Perceiving Motion We perceive movement when an image moves across the retina of our eyes. Two factors contribute to how we perceive movement: 1. The background against which an object moves and 2. The size of the object. Apparent motion - We can also be fooled into thinking something is moving when it is not. Ex. Flipbooks: When you quickly flip through the pages of a flipbook, the still images appear to move due to the rapid change in position across the pages.  Perceiving Depth Monocular Depth Cues - Artists use monocular cues called pictorial cues to create an illusion of depth.  Perceptual Constancies We also know that, when things change position or distance in relation to us, they remain the same. The images on our retinas change shape and size as objects move through space. Perceptual constancy - The ability of the brain to preserve perception of objects in spite of changes in retinal image when an object changes in position or distance from the viewer.  Hearing Just as vision starts when we sense light waves, hearing begins when we sense sound waves. Sound waves must travel through a medium (air, water, or solid materials) or we cannot hear them. Ex. In space, where there is no air or other medium, sound waves cannot travel, so there is complete silence. This is why astronauts can’t hear each other in space unless they use radios or other devices that transmit sound through other means. Sound waves travel much more slowly than light waves, which is why you hear thunder after you have seen lightning. Hertz (Hz) - a unit expressing the frequency of sound waves. One hertz equals one cycle per second Decibels (dB) - a unit expressing the loudness of a sound  The Ear Outer Ear - The outer ear is shaped to funnel sound waves to the eardrum, a thin membrane that vibrates in response to sound waves. Sound vibrations travel to the eardrum (tympanic membrane). Middle Ear - Transmit sound waves that causes vibration to the eardrum. Consist of t three small bones which are the hammer, anvil, and stirrup. Inner Ear - The stirrup (stapes) is connected to the oval window which is a membrane in the inner ear. When the stirrup vibrates, it makes the oval window vibrate.Which play a key role in maintaining a sense of balance. Cochlea - A bony tube of the inner ear, which is curled like a snail's shell and filled with fluid. Basilar membrane - A membrane that runs through the cochlea; contains the hair cells.  Perception of Loudness and Pitch Place theory suggests that we perceive the pitch of a sound based on where along the basilar membrane (inside the cochlea of the inner ear) the vibration occurs. Different areas of the membrane respond to different pitches: High-pitched sounds cause vibrations near the beginning of the membrane. Low-pitched sounds cause vibrations further along the membrane. Ex. When you hear a high-pitched sound, like a whistle, the vibrations occur near the base of the basilar membrane. In contrast, when you hear a low- pitched sound, like a deep drum beat, the vibrations occur further along the membrane, towards the apex. This difference in vibration location helps your brain identify whether the sound is high or low in pitch.  Deafness Conductive deafness occurs when there is damage to the structures in the middle ear, such as the eardrum or the small bones (ossicles) that transmit and amplify sound from the outer ear to the inner ear. This type of hearing loss is common in older adults. Hearing aids can often help by amplifying the sound, making it easier for those with conductive deafness to hear. Sensorineural deafness is caused by damage to the inner ear, particularly the loss of hair cells in the cochlea, or damage to the auditory nerve. This type of hearing loss can result from factors like diseases, aging, or exposure to very loud noises. People with sensorineural deafness often have difficulty hearing certain pitches more than others. Unlike conductive deafness, this type of hearing loss is usually permanent and not easily fixed with hearing aids, though cochlear implants can sometimes help.  THE OTHER SENSES SMELL - has an important role in human behavior. It contributes to the flavor of foods, for example. If you did not have a sense of smell, an onion and an apple might taste the same to you olfactory nerve - the nerve that transmits information concerning odors from olfactory receptors to the brain taste cells - receptor cells that are sensitive to taste taste buds - the sensory organs for taste; they contain taste cells and are located mostly on the tongue Phantom limb pain is when a person feels pain in a limb that has been amputated. This pain occurs because nerves in the remaining part of the limb (stump) are still active, sending signals to the brain as if the limb were still there. Gate theory of pain suggests that the spinal cord has a "gate" mechanism that controls the flow of pain signals to the brain. Since it can only handle a limited amount of information at once, when other sensory signals (like touch or pressure) are active, they can "close the gate" and reduce the perception of pain in a specific area. This is why rubbing a bumped elbow can help ease the pain it activates other signals that compete with the pain signals.  Is there perception without sensation? Perception can occur without direct sensation, a phenomenon often referred to as perceptual illusions or hallucinations. Examples: Phantom Limb Sensation: People who have lost a limb may still feel sensations, like itching or pain, in the missing limb due to the brain's perception. Hallucinations: Seeing, hearing, or feeling things that aren’t there, as seen in some mental health conditions, where the brain creates perceptions without actual sensory input. In these cases, the brain generates perceptions that do not directly correspond to external sensory input