Unit 3: Sensation & Perception

Colorblindness

- 1/50 people, usually male because the defect is genetically sex linked Color blindness is caused when one or more of the color cone cells are absent, detect a different color than normal, or if they simply do not work. Cone cells are cells in the retina detect color and there are three types of cones that see color which are red, green, and blue. The brain uses input from these cone cells to determine what color we perceive. That is why a malfunction in the cone cells will cause color blindness. Color-deficient vision (not actually blind to all colors) - Lack functioning red or green sensitive cones, or sometimes both - Vision is monochromatic or dichromatic instead of trichromatic making it impossible to distinguish green and red.

Touch

- Aids in development - Some spots on the skin are especially sensitive to PRESSURE, others to WARMTH, others to COLD, & others to PAIN - Our "sense of touch" is a mixture of these four basic and distinct skin senses, and our other skin sensations are variations of pressure, warmth, cold and pain. EX: Stroking adjacent pressure spots creates a tickle - Cognition influences our brain's sensory response EX: A self-administered tickle produces less somatosensory cortex activation than does that same tickle from someone else.

Understanding pain

- Our experience of pain reflects both bottom-up sensations and top-down cognition - Pain is a biopsychosocial event. So, pain experiences vary widely, from group to group and from person to person. BIOLOGICAL INFLUENCES - Pain is a physical event produced by your senses Why pain is different from other sensations: - No one type of stimulus triggers pain the way light triggers vision - No specialized receptors process pain signals the way retina receptors react to light rays. - Instead, specialized receptors called nociceptors (mostly in skin, but also in muscles and organs) detect harmful temperatures, pressure, or chemicals 1. Experience of pain depends on inherited genes and physical characteristics - EX: Genetic differences in endorphin production 2. Gate-control theory: the theory that the spinal cord contains a neurological "gate" that controls the transmission of pain messages to the brain - Small spinal cord nerve fibers conduct most pain signals. When tissue is injured, the small fibers activate and open the gate. The pain signals travel to the brain, causing pain to be experienced. - How chronic pain can be treated: Large-fiber activity (stimulated by massage, electrical stimulation, or acupuncture) can close the gate and block pain signals. Brain-to-spinal-cord messages can also close the gate. So, chronic pain can be treated both by "gate-closing" simulation like massage, and by mental activity, like distraction Pain is not just a physical phenomenon of injured nerves sending impulses to a brain or spinal cord area. The brain can also create pain as in PHANTOM LIMB SENSATIONS after a limb amputation - Without normal sensory input, the brain may misinterpret and amplify spontaneous but irrelevant central nervous activity - The brain is prepared to anticipate that it will be getting info from a body that has limbs - Phantom limbs can haunt other senses: > Hearing: tinnitus- the phantom sound of ringing in the ears that accompanied by auditory brain activity > Vision: phantom sights - non threatening hallucinations > Tasting and smelling: phantom tastes or smells with those that have nerve damage in those systems- Ex: Water tasting sweet - Point to remember: We feel, see, hear, taste, and smell with our brain, which can sense even without functioning senses. PSYCHOLOGICAL INFLUENCES 1. ATTENTION to pain influences our perception of pain 2. We edit our MEMORIES of pain, which often differ from the pain we actually experienced. - People overlook a pain's duration - Memory records 2 factors: 1) their pain's peak moment (which can lead them to recall variable pain, with peaks as worse) 2) How much pain they felt at the end (less pain at the end = a less painful experience as a whole) 3. Learning based on experience 4. Expectations SOCIAL-CULTURAL INFLUENCEs 1. Pain is a product of our attention, our expectations, and our culture 2. Our perception of pain varies with our social situation and our cultural traditions 3. We perceive more pain when others seem to be experiencing pain 4. Empathy for others pain causes brain activity to partly mirror the activity of the actual brain in pain

Color processing occurs in 2 stages

1. The retina's red, green, and blue cones respond in varying degrees to different color stimuli, as the Young-Helmholtz trichromatic theory suggested 2. The cone's responses are then processed by opponent-process cells as Hering's opponent-process theory proposed.

Prosopagnosia (face blindness)

Inability to recognize faces; sensation is normal but perception is ALMOST normal

Selective Attention

The focusing of conscious awareness of a particular stimulus

Sensation

The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment

Young-Helmholtz trichromatic theory

The theory that the retina contains three different types of contains three different types of color receptors - one most sensitive to red, one to green, one to blue - which, when stimulated in combination, can produce the perception of any color.

Perceptual Organization

- Form Perception - Depth Perception - Motion Perception - Perceptual Constancy

Pain

- Pain is the body's alarm system to warn something has gone wrong - Psychological purposes: provides a contrast that amplifies our experiences of pleasure, enhances our self-awareness, arouses others' emphathy and promotes social connections

Sensory receptors

Sensory nerve endings that respond to stimuli. Nervous system transmits this information to the brain

Difference Thresholds

The minimum difference between two stimuli required for detection 50% of the time. We experience the difference threshold as just noticeable difference (or jnd) - Detectable difference increases with the size of stimulus Weber's Law - Ernst Weber, late 1880s - The principle that, to the perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount) - Exact percentage varies, depending on the stimulus

Sensory interaction

The principle that one sense may influence another, as when the smell of food influences its taste Ex: - Smell has a heavy influence on taste - Touch can influence taste too (texture of stale foods) - Smell + texture + taste = flavor - Vision and hearing can influence each other (ex. using captions to watch videos can make us hear better) McGurk Effect: a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. Embodied cognition: The influence of bodily sensations, gestures, and other states on cognitive preferences and judgments - Brain circuits processing our physical sensations sometimes interact with brain circuits responsible for cognition - Ex: Physical warmth may promote social warmth; social exclusion can literally feel cold; judgments of others may also mimic body sensations Synesthesia: The stimulation of one sense (such as hearing sound) triggers an experience of another (such as seeing color)

Audition

The sense or act of hearing

Perceptual interpretation

the process of generating meaning from sensory experience

The Stimulus Input: Sound Waves

- Air molecules, each bumping into the next, create waves of compressed and expanded air. Our ears detect brief air pressure changes Sound waves vary in shape: - Height (amplitude), determines their perceived loudness - Length (frequency: the number of complete wavelengths that pass a point in a given time), determines the pitch (high or low tone) we experience. - Long waves have low frequency & pitch; short waves have high frequency & pitch - Great amplitude = loud sounds; small amplitude = soft sounds Amplitude is measured in decibels - Zero decibels = the absolute threshold for hearing - Every 10 decibels correspond to a tenfold increase in sound intensity - Ex. A normal conversation (60 decibels) is 10,000 times more intense than a 20-decibel whisper - If prolonged, exposure to sounds above 85 decibels can promote hearing loss

Retina's neural layers

- At the entry level, the retina's neural layers don't just pass along electrical impulses, they also help to encode and analyze sensory information - Any given retinal area relays its info. to a corresponding location in your visual cortex, in the occipital lobe.

The optic nerve

- Information highway from the eye to the brain - Can send nearly 1 million messages at once through its 1 million ganglion fibers - Price for this speed: The blind spot (the point at which the optic nerve leaves the eye, creating a "blind spot" because no receptor cells are located there).

Rods and cones

- Our eyes' light-sensitive photoreceptors - differ in where they're found/ what they do CONES - cluster in and around the fovea (the central focal point in the retina, around which the eye's cones cluster) - Many cones have their own hotline to the brain: one cone transmits its message to a single bipolar cell, which relays the message to the visual cortex where a large area receives input from the fovea - These direct connections preserve the cones' precise information, making them better able to detect fine detail - Although cones can detect white, they also enable you to perceive color. But in dim light, they become unresponsive, so you see no colors. - Number: 6 million - Location in retina: center - Sensitivity in dim light: low - Color sensitivity: High - Detail sensitivity: High RODS - Located in the retina's outer regions - Sensitive in dim light - Enable black and white vision - Have no hotline to the brain. Instead, several rods pool their faint-energy output and funnel it onto a single bipolar cell, which sends the combined message to the brain. - Number: 120 million - Location in retina: periphery - Sensitivity in dim light: high - Color sensitivity: low - Detail sensitivity: low Each provide a special sensitivity - cones to detail and color and rods to faint light and peripheral motion - Ex: Stare at a word on a page and the sides appear blurred. Words on the side lack detail because their image is striking the retina's outer regions, where rods predominate - When biking/driving, rods help detect a car in peripheral vision before you can perceive its details

Controlling pain

- Pain is both a physical and psychological phenomenon, so it can be treatable both physically and psychologically - Our brain releases endorphins, which is a natural painkiller in response to severe pain or vigorous exercise. 1. Placebos - Dampen the central nervous system's attention and responses to painful experiences- mimicking painkilling drugs - Triggers the brain to respond by dispensing endorphins 2. Distraction - Drawing attention away from the painful stimulation is an effective way to activate brain pathways that inhibit pain and increase pain tolerance - Because pain is in the brain, diverting the brain's attention may bring relief

ESP - Perception Without Sensation?

- Perception is the product of SENSATION, COGNITION, and EMOTION Extrasensory Perception (ESP): THe controversial claim that perception can occur apart from sensory input; includes telepathy, clairvoyance, and precognition - Telepathy: Mind-to-mind communication - Clairvoyance: Perceiving remote events, such as a house on fire in another state - Precognition: perceiving future events, such as an unexpected death in the next month Parapsychology: The study of paranormal phenomena, including ESP and psychokinesis Premonitions or pretensions? - Physics are mostly inaccurate in their predictions, but can be accurate by coincidence and their visions can help.

Hearing different pitches

- Place theory and frequency theory work together to enable our perception of pitch - Place theory best explains how we sense high pitches. Frequency theory, extended by the volley principle, explains how we sense low pitches - Combination of place + frequency theories explain how we sense pitches in the intermediate range

Retina adaption to light

- Pupils dilate in the dark to allow more light for the retina - Fully adapting takes 20 min or more - this period of dark adaptation matches the average natural twilight transition between the sun's sertting and darkness

Feature Detection

- Scientists David Hubel and Torsten Wiesel worked on studying feature detectors Feature detectors: Nerve cells in the brain's visual cortex that respond to specific features of the stimulus, such as shape, angle, or movement. - Recieve info. from individual ganglion cells in the retina. Then, pass this specific info. to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns. - We have a "vast visual encyclopedia" distributed as specialized cells. These cells respond to one type of stimulus, like a specific gaze, head angle, posture, or body movement. Other supercell clusters integrate this info. and fire only when the cues collectively indicate the direction of someone's attention and approach. This instant analysis, which aided our ancestors survival, also helps a soccer player anticipate where to strike the ball. One temporal lobe area by the right ear enables the perception of faces and the recognition of faces from varied viewpoints - If it were damaged, you might recognize other forms and objects, but not familiar faces. - Fusiform face area: If stimulated, you might spontaneously see faces Brain's face perception occurs separately from its object perception - MRI (fMRI) scans show different brain areas activating when people viewed varied objects - Brain activity is so specific that brain scans can show if people are looking at a chair, face, or shoe based on the pattern of their brain activity.

Afterimages

- Seeing the opponent colors of an image after staring at an image - Explains why people blind to red and green often still see yellow

Responding to Loud and Soft Sounds

- The brain interprets loudness from the number of activated hair cells - Really loud sounds may seem loud to people with or without normal hearing. We differ in our perception of soft sounds. B/c if a hair cell loses sensitivity to soft sounds, it may still respond to loud sounds

Frequency Theory (temporal theory)

- The brain reads pitch by monitoring the frequency of neural impulses traveling up the auditory nerve. The whole basilar membrane vibrates with the incoming sound wave, triggering neural impulses to the brain at the same rate as the sound wave. - Problem: An individual neuron can't fire faster than 1000 times per second. How, then, can we sense sounds with frequencies above 1000 waves per second Answer: The volley principle: Neural cells can alternate firing. By firing in rapid succession, they can achieve a combined frequency above 1000 waves per second.

Selective Attention and Accidents

- Using your phone while driving causes selective attention to shift from phone usage and driving, causing more accidents. - 4x higher chance of crashing while using your phone, equal to the risk of drunk driving

Place theory

- We hear different pitches because different sound waves trigger activity at different places along the cochlea's basilar membrane. So, the brain determines a sound's pitch by recognizing the specific place (on the membrane) that is generating the neural signal. - The cochlea vibrates in response to sound. High frequencies produce large vibrations near the beginning of the cochlea's membrane. Low frequencies vibrate more of the membrane and are harder to locate. - Problem: Place theory can explain how we hear high pitches sounds, but not low-pitched sounds.

Hearing process

1. Begins when sound waves strike your eardrum, causing this tight membrane to vibrate 2. Middle ear (the chamber between the eardrum and cochlea containing 3 tiny bones [hammer, anvil, and stirrup] that concentrate the vibrations of the eardrum on the cochlea's oval window) picks up the vibrations and transmits them to the cochlea (a coiled, bony, fluid-filled tube in the inner ear [the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs] ; sound waves traveling through the cochlear fluid trigger nerve impulses) 3. The incoming vibrations then cause the cochlea's membrane covered opening (the oval window) to vibrate, jostling the fluid inside the cochlea 4. This movement causes ripples in the basilar membrane, bending the hair cells lining its surface 5. The hair cell movements in turn trigger impulses in adjacent nerve cells, whose axons converge to form the auditory nerve. The auditory nerve carries the neural messages to your thalamus and then to the auditory cortex in the temporal lobe.

The Eye (process of vision)

1. Light enters the eye through the cornea (the eye's protective outer layer, covering the pupil and iris), which bends light to help provide focus. 2. The light then passes through the pupil (the adjustable opening in the center of the eye through which light enters) 3. Surrounding the pupil and controlling its size is the iris (colored muscle that dilates or constricts in response to light intensity) - Iris responds to cognitive and emotional states: Sunny sky, iris will constrict making pupil smaller; Constrict when you feel disgust, dilate to feeling love 4. After passing through the pupil, light hits the transparent lens (the transparent structure behind the pupil that changes shape to help focus images on the retina) in your eye. 5. The lens focuses the light rays into an image on your retina (the light-sensitive inner surface of the eye, containing the receptor rods and cones + layers of neurons that begin the processing of visual information) 6. To focus the rays, the lens changes its curvature and thickness in a process called accommodation (the process by which the eye's lens changes shape to focus near or far objects on the retina) - Nearsightedness (myopia) - when the lens focuses the image on a point in front of the retina. 7. Rays from the top of the object strike the bottom of the retina and those from the right side of the object strike the left side of the retina, so the image on the retina of the object appears upside down & reversed. 8. The retina doesn't "see" a whole image. Rather, its millions of receptor cells convert particles of light energy into neural impulses and forward those to the brain, which reassembles them into what we perceive as an upright-seeming image. Along the way, visual information processing percolates through progressively more abstract levels. All this happens with astonishing speed.

SUMMARY

1. Scene --> 2. Retinal Processing (receptor rods & cones-> bipolar cells -> ganglion cells) --> 3. Feature Detection (Brain's detector cells respond to specific features like edges, lines, and shapes) --> 4. Parallel Processing (Brain cell teams process combined info. abt color, movement, form, and depth) 5. Recognition (Brain interprets the constructed image based on info. from stored images)

A single light-energy particle's path

1. Threads through the retina's spare outer layer of cells. Then, reaching the back of the eye, it encounters the retina's 130 million buried receptor cells, the rods (retinal receptors that detect black, white, and gray and are sensitive to movement; necessary for peripheral and twilight vision when cones don't respond) and cones (retinal receptors that are concentrated near the center of the retina and that function in daylight or in well lit conditions. Cones detect fine detail and give rise to color sensations) 2. There, the light energy triggers chemical changes. That chemical reaction sparks neural signals in nearby bipolar cells. Then the bipolar cells activate neighboring ganglion cells, whose axons twine together to form the optic nerve (the nerve that carries neural impulses from the eye to the brain). 3. After a momentary stop at the thalamus, the information travels to the final destination, the visual cortex, in the occipital lobe in the back of the brain.

Cochlear implant

A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes

Conduction hearing loss

A less common form of hearing loss; caused by damage to the mechanical system - the eardrum and middle ear bones - that conduct sound waves to the cochlea.

Perceptual set

A mental predisposition to perceive one thing and not another. Affects, top-down, what we hear, taste, feel, and see - Context of spoken words can determine what you HEAR - Expectations can influence TASTE perceptions - Stereotypes about gender (perceptual set) can color perception What determines our perceptual set? - Through experience, we form concepts, or schemas, that organize and interpret unfamiliar info. Influence how we apply top-down processing to interpret ambiguous sensations

Gestalt

An organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.

Motion Perception

Brain computes motion based partly on its assumption that shrinking objects are retreating and enlarging objects are approaching. - In young children, the ability to correctly perceive motion is not fully developed, which puts them at risk for pedestrian accidents An adult brain can be tricked in motion perception: When large and small objects move at the same speed, the large objects appear to move more slowly. Ex: Jumbo jets seem to land more slowly than little jets Stroboscopic movement: a phenomenon in which the brain perceives a rapid series of slightly varying images as continuous movement Phi phenomenon: an illusion of movement created when two or more adjacent lights blink on and off in quick succession. We perceive it as one single light moving back and forth.

Damage to hair cell receptors

Caused by diseases, biological changes linked with heredity and aging, and prolonged exposure to ear-splitting noise or music

Top-down processing

Constructs perceptions from this sensory input by drawing on your experience and expectations.

Transduction

Conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brain can interpret. All of our senses: - Receive sensory stimulation, often using specialized receptor cells - Transform that stimulation into neural impulses - Deliver the neural info to our brain Psychophysics: the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.

Cocktail party effect

Demonstrates our ability to attend to one voice among a sea of other voices. When another voice speaks your name, your cognitive rader, operating on your mind's other track (and in your right frontal cortex), instantly brings that unattended voice into consciousness.

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation - Offers an important benefit: freedom to focus on informative changes in our environment - Also influences how we perceive emotions - Point to remember: Our sensory system is alert to novelty; bore it with repetition and it frees our attention for more important things. We see this principle again and again; we perceive the world not exactly the way it is, but as it is useful for us to perceive it.

Locating sounds

Due to placement of our two ears, we have stereophonic ("three-dimensional") hearing Benefits to this placement: - A noise next to our right ear makes right ear receive a more intense sound, and it will receive the sound slightly sooner than the left ear. - Intensity difference and time lag are extremely small. Our supersensitive auditory system can detect such minute differences- and locate the sound.

Light Energy and Eye Structures

Eyes receive light energy and transduce (transform) it into neural messages. From this neural input, our brain creates what we consciously see.

Inattentional Blindness

Failing to see visible objects when our attention is directed elsewhere - At the level of conscious awareness, we are "blind" to all but a tiny sliver of visual stimuli - Attention is powerfully selective. Your conscious mind is in one place at a time - Change blindness: Failing to notice changes in the environment; a form of inattentional blindness - Change deafness: Failing to notice changes between voices and sounds, a form of inattentional blindness

Form Perception

Figure-ground: The organization of the visual field into objects (the figures) that stand out from their surroundings (the ground) - Our first perceptual task - Also applies to hearing Grouping: The perceptual tendency to organize stimuli into coherent groups - Our mind brings order and form to other stimuli by following certain rules for grouping: 1. Proximity: We group nearby figures together. 2. Continuity: We perceive smooth, continuous patterns rather than discontinuous ones. 3. Closure: We fill in gaps to create a complete, whole object

Taste

Gustation: our sense of taste Taste's sensations + their survival functions: 1. Sweet; indicates energy source 2. Salty; indicates sodium essential to physiological processes 3. Sour; indicates potentially toxic acid 4. Bitter; indicates potential poisons 5. Umami (savory, meaty taste best experienced as the flavor enhancer MSG); proteins to grow + repair tissue Taste is a chemical sense (taste process:) 1. 200 or more taste buds on the tongue, each containing a pore that catches food chemicals 2. In each taste bud pore, 50-100 taste receptor cells project antenna-like hairs that sense food molecules 3. Some receptors respond mostly to sweet-tasting molecules, others to salty, sour, umami, or bitter 4. Each receptor transmits its message to a matching partner cell in the brain's temporal lobe Supertasters- have more taste buds than other's enabling them to experience more intense tastes. They can also taste some things that the rest of us cannot As you age, taste bud number and taste sensitivity decreases Expectations can influence taste Ex: $90 wine when it was really $10 tasted better

Sensorineural hearing loss (nerve deafness)

Hearing loss caused by damage to the cochlea's hair cell receptors or the auditory nerve; most common form of hearing loss

Absolute Thresholds

Minimum amount of stimulus energy needed to detect a particular stimulus 50% of the time Ex: - We can see the light of a candle in the dark 30 miles away - Feel the wing of a bee falling on our cheek - Smell a single drop of perfume in a three-room apartment Gustav Fechner (1801-1887): German scientist and philosopher, studied the edge of our awareness of these faint stimuli, which he called their absolute thresholds Signal Detection Theory: A theory predicting how & when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and alertness. Subliminal: Stimuli you cannot consciously detect 50% of the time; below one's absolute threshold for conscious awareness Priming: The activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response

Smell

Olfaction - the sense of smell Smell is a chemical sense (like taste) 1. Smell is experienced when molecules of a substance carried in the air reach a tiny cluster of receptor cells at the top of each nasal cavity 2. These 20 million olfactory receptors respond selectively. Instantly, they alert the brain through their axon fibers 3. The receptor cells send messages to the brain's olfactory bulb, and then onward to the temporal lobe's primary smell cortex, and to the parts of the limbic system involved in memory and emotion Olfactory neurons bypass the brain's sensory control center, the thalamus, because they are part of an old, primitive sense. - Ancestors sniffed for food and predators eons before our cerebral cortex had fully evolved - Ancestors smelled molecules called pheromones, secreted by other members of their species. Some pheromones serve as sexual attractants Odors come in many different shapes & sizes, so it takes many different receptors to detect them - A large family of genes designs the 350 receptor proteins that recognize particular oder molecules. These receptor proteins are embedded on the surface of the nasal cavity neurons. - Odor molecules slip into these receptors like a lock and key. Yet, we don't have a distinct receptor for each detectable odor. Odors trigger combinations of receptors in patterns that are interpreted by the olfactory cortex. Odor molecules bind to different receptor arrays, producing at least 1 trillion odors we could potentially discriminate. Survival purpose for smell: We each have our own chemical signature scent Smells appeal 1. depends on cultural influences EX: Wintergreen in US is associated with candy and gum and people tend to like it. in Britain, wintergreen is associated with medicine and people find it less appealing. 2. Smells can change emotions based on past experiences/memories EX: Certain odors can evoke unpleasant/pleasant emotions based on experiences with that odor We have a remarkable capacity to recognize long-forgotten odors and their associated memories - Odor's power to evoke feelings and memories explained: A hotline runs between the brain area receiving info from the nose and the brain's ancient limbic centers associated with memory + emotion. Our ability to identify scents 1. Gender and age influence - Women & young adults have the best sense of smell 2. Physical condition influences - Smokers and people w/ Alzheimers', Parkinsons', or alcohol use disorder typically have a diminished sense of smell

Kinethesia

Our movement sense; our system for sensing the position + movement of individual body parts - There are millions of position + motion sensors in muscles, tendons, and joints all over the body. These sensors provide immediate and constant feedback to the brain - Vision interacts with kinesthesia

Vestibular sense

Our sense of body movement and position that enables our sense of balance - Two structures in the inner ear are responsible for this sense of equilibrium: 1. Fluid-filled semicircular canals 2. Pair of calcium crystal-filled vestibular sacs - When your head rotates or tilts, the movement of these organs stimulates hair-like receptors, which send nerve signals to your cerebellum at the back of the brain, enabling you to sense your body position and maintain your balance. - If you twirl around & then come to an abrupt halt, neither the fluid in your semicircular canals nor your kinesthetic receptors will immediately return to their neutral state which causes a DIZZY after effect that fools your brain with the sensation that you're still spinning > This illustrates a principle that underlies perception illusions: Mechanisms that normally give us an accurate experience of the world can fool us. - Vestibular sense is FAST. If you slip, your vestibular senses automatically and instantly order your skeletal response, well before you consciously decide how to right yourself.

Perceptual Constancy

Perceiving objects as unchanging (having consistent color, brightness, shape, and size) even as illumination and retinal images change - A top-down process Color and Brightness Constancies 1. Color constancy: perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object. - We see color b/c of our brain's computations of the light reflected by an object relative to the objects surrounding it 2. Brightness/lightness constancy: perceiving an object as having a constant brightness even as its illumination varies. - Depends on relative luminance: the amount of light an object reflects relative to its surroundings Context govers our perceptions. We perceive objects not in isolation but in their environmental context. Shape and Size Constancies 1. Shape constancy: Perceiving the form of familiar objects as constant even while our retinas receive changing images of them - Our brain manages this feat b/c visual cortex neurons rapidly learn to associate different views of an object - Perceive an object as having an unchanging size. Even when distance from it varies. Illustrates the close connection between perceived distance and perceived size.

Context, Motivation, and Emotion

Perceptual set influences how we interpret stimuli. But our immediate context, and the motivation and emotion we bring to a situation, also affect our interpretations 1. Context - Context of a situation can change our perceptions of that situation - Cultural context helps inform our perceptions 2. Motivation - Motives give us energy as we work toward a goal. Like context, they can bias our interpretations of neural stimuli. - Desirable objects seem closer than they are. This perceptual bias energizes our going for it. - Hills and destinations seem harder & farther than when we are heavy + tired 3. Emotion - Emotions can shove our perceptions in one direction or another EX: When angry, people more often perceive neutral objects as guns - Emotions and motives color our social perceptions too Through top-down processing, our experiences, assumptions, expectations- and even our context, motivation, and emotions, can shape and color our views of reality.

Parallel Processing

Processing many aspects of a problem simultaneously: The brain's natural mode of info. processing for many functions, including vision. - To analyze a visual scene, the brain divides it into subdimensions - MOTION, FORM, DEPTH, COLOR - and works on each aspect simultaneously. We construct our perceptions by integrating the separate but parallel work of these different visual teams. - To recognize a face, your brain integrates info. projected by your retinas to several visual cortex areas and compares it with stored info., thus enabling your fusiform face area to recognize the face. This stored info. is likely distributed over a vast network of cells. Blindsight - Experienced after a stroke or surgery damaged the brains visual cortex - There's a second "mind" (a parallel processing system) operating unseen. These separate visual systems for perceiving and for acting illustrate once again the astonishing dual processing of our two-track mind.

Experience and visual perception

Restored vision and sensory restriction: - People who have their vision restored later in life can distinguish figure from ground and could differentiate colors- suggests that these aspects of perception are innate. But they often remained unable to visual recognize objects that were familiar by touch. - For normal sensory and perceptual development, there is a critical period: an optimal period when exposure to certain stimuli or experiences is required. Perceptual adaptation: The ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field. - So, in part we LEARN to perceive the world as we constantly adjust to changed sensory input.

Bottom-up processing

Starts at the sensory receptors and works up to higher levels of processing

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 Visual cliff: a lab device for testing depth perception in infants and young animals - Proved infants can perceive depth and that depth perception is partly innate Binocular cues: a depth cue, such as retinal disparity, that depends on the use of two eyes - Used to judge the distance of nearby objects 1. Convergence: The inward angle of the eyes focusing on a near object 2. Retinal disparity: A binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance - the greater the disparity (difference) between the two images, the closer the object Monocular cues: a depth cue, such as interposition or linear perspective, available to either eye alone 1. Relative height: We perceive objects higher in our field of vision as farther away 2. Relative size: IF we assume two objects are similar in size, most people perceive the one that casts the smaller retinal image as farther away. 3. Interposition: If one object partially blocks our view of another, we perceive it as closer 4. Relative motion: As we move, objects that are stable may appear to move. If you fix your gaze on some point while in motion, the objects beyond the fixation point will appear to move with you. Objects in front of the point will appear to move backward. The farther an object is from the fixation point, the faster it will seem to move. 5. Linear perspective: Parallel lines appear to meet in the distance. The sharper the angle of convergence, the greater the perceived distance 6. Light and shadow: Shading produces a sense of depth consistent with our assumption that light comes from above.

Perception

The process of organizing and interpreting sensory info, enabling us to recognize meaningful objects and events

Opponent-process theory

The theory that opposing retinal processes (red-green, blue-yellow, 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 - Some neurons in both the retina and the thalamus are turned "on" by red but turned "off" by green - "Red" and "green" messages can't both travel at once, so they are opponents - Explains negative afterimages: staring at a color tired that color's response. Then staring at a white area, it includes all the opponent color. The tired colors opponent color is shown because that part of the pair fired normally.

The Stimulus Input: Light Energy

The wavelengths we see: - Wavelengths visible to the human eye extend from the shorter waves of blue-violet light to the longer waves of red light. - Only a thin slice of electromagnetic energy We see color as pulses of electromagnetic energy that our visual system perceives as a color. Wavelength: the distance from the peak of one light or sound wave to the peak of hte next. Electromagnetic wavelengths vary from short gamma rays to long radio waves. - Wavelengths determine hue: the dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so on. - A light waves amplitude determines its intensity: the amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave's amplitude.

Summarizing the Senses (Table)

Vision - Source: Lightwaves striking the eye - Receptors: Rods and cones in the retina - Key brain areas: Occipital lobes Hearing - Source: Sound waves striking the outer ear - Receptors: Cochlear hair cells (cilia) in the inner ear - Key brain areas: Temporal lobes Touch - Source: Pressure, warmth, cold, harmful chemicals - Receptors: Receptors (including pain sensitive nociceptors), mostly in the skin, which detect pressure, warmth, cold, and pain - Key brain areas: Somatosensory cortex Taste - Source: Chemical molecules in the mouth - Receptors: Basic taste receptors for sweet, sour, salty, bitter, and umami - Key brain areas: Frontal temporal lobe Smell - Source: Chemical molecules breathed in through the nose - Receptors: Millions of receptors at top of nasal cavities - Key brain areas: Olfactory bulb Body position - Kinesthesia - Source: Any change in position of a body part, interacting with vision - Receptors: Kinesthetic sensors in joints, tendons, and muscles - Key brain areas: Cerebellum Body movement - Vestibular sense - Source: Movement of fluids in the inner ear caused by head/body movement - Receptors: Hair-like receptors in the ears' semicircular canals and vestibular sacs - Key brain areas: Cerebellum