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Sensation & Perception
Chapter4
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Sensation Def:the stimulation of sensory receptors and the transmission of sensory information to the central nervous system (brain and spinal cord)
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Sensation Stimulation of the senses is mechanical; results from sources of energy like light and sound or from presence of chemicals, as in smell and taste
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Perception Not mechanical but interpreted
Def: the process by which sensations are organized into an inner representation of the world
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Perception It reflects learning and expectations and the ways in which we organize incoming information about the world. Personal reality relies on: -vision, hearing, smell, taste, touch
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Absolute Threshold The weakest amount of a stimulus that can be told apart from no stimulus at all Table 4.1 pg.126 Ex: Taste About 1 teaspoon of sugar dissolved in 2 gallons of water
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Absolute Threshold There are individual differences in absolute thresholds Ex: Pitch -the highness or lowness of a sound, as determined by the frequency of the sound waves
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Difference Threshold The minimal difference in intensity required between two sources of energy so that they will be perceived as being different (Ex: Weight Lifting-2 lbs needed before noticing a difference) Table 4.2 pg.127 (toothpick ex)
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Signal-Detection Theory
The view that the perception of sensory stimuli involves the interaction of physical, biological, and psychological factors
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Signal-Detection Theory
The degree to which the signal can be distinguished from background noise Ex: easier to hear a friend’s voice in a quiet room rather than a room filled with people clinking silverware and chatting
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Signal-Detection Theory
Psychological factors include: -motivation, expectations, learning -emphasizes the aspects of detecting and responding to signals Ex: studying and baby’s cry
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Sensory Adaptation The process by which we become more sensitive to stimuli of low magnitude and less sensitive to stimuli of relatively constant magnitude Sensitization vs. Desensitization
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Sensitization The process of becoming more sensitive to stimulation (positive adaptation) Ex: Dark theater we become more sensitive to faces and objects as time elapses
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Desensitization Becoming less sensitive to ongoing stimulation
constant light appears to grow dimmer Live in city, become desensitized to traffic sounds
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Vision & Dimensions of Color
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The Eye Pages Know the different parts of the eye and their functions for the test
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Rods and Cones Photoreceptors in the retina
About 125 million rods and 6.5 million cones are distributed across the retina
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Rods Rod-shaped photoreceptors that are sensitive only to the intensity of light They allow us to see in black and white
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Cones Cone-shaped photoreceptors that transmit sensations of color
Provide color vision
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Light Adaptation Dark adaptation: adjusting to lower lighting
Movie theater: -Cones: permit perception of color, reach maximum adaptation to darkness in 10 minutes -Rods: allow perception of light and dark only, are more sensitive and continue to adapt to darkness for up to about 45 minutes
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Light Adaptation cont…
Adaptation to brighter lighting conditions takes place more rapidly Emerging from dark theater: at first you’ll be surprised by featureless blaze around you. Within a minute or so, the brightness will have dimmed and objects will have regained their edges
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Dimensions of Color Wavelength of light determines its color, or hue
Brightness of a color is its degree of lightness or darkness The brighter the color, the lighter it is Create your color wheel: red, orange, yellow,green, blue, purple
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Warm and Cool Colors Warm:red/orange/yellow colors side (burn)
Warm colors seem to advance toward the viewer Cool:green/blue (ocean and sky) Cool colors seem to recede into the distance
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Saturation The degree of purity of a color
Pure hues have the greatest intensity, or brightness Saturation (brightness) decreases when another hue or black, gray, white is added
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Saturation Hue: adding black Tint: adding white
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Complementary The colors across from one another on the color wheel
Red-green Blue-yellow
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Primary Colors Colors that cannot be produced by mixing pigments of other hues Red Blue Yellow
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Secondary Colors derived by mixing primary colors
Orange: mixing (red/yellow) Green: mixing (blue/yellow) Purple: mixing (red/blue)
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Tertiary Colors derived by mixing primary and adjoining secondary colors Yellow-green Bluish-purple
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Afterimage The lingering visual impression made by a stimulus that has been removed Look on page 138 Perception of the complementary color after first color is removed
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Afterimage Similar or comparable colors
Hues that lie next to one another on the color wheel, forming families of related colors Yellow and orange Orange and red Green and blue Intermarry: blue with violent, violet with red and so on…
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Visual Perception
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Color Blindness Trichromat: A person with normal color vision
Monochromat:A person who is sensitive to black and white only and hence color blind Dichromat: A person who is sensitive to black and white and either red-green or blue-yellow and hence partially color blind
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Color Blindness Partial blindness is more common than total color blindness Partial color blindness is a gender or sex-linked trait that strikes mostly males (found on X chromosome)
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Visual Perception Relies on our knowledge, expectations, and motivations An active process by which we interpret the world around us Meaningless splotches handout
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Perceptual Organization
The tendency to integrate perceptual elements into meaningful patterns
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Figure-ground Perception
When figure-ground relationships are ambiguous (capable of being interpreted in various ways), our perceptions tend to be unstable, to shift back and forth. The Rubin Vase The Necker Cube Gestalt Rules for Organization
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Gestalt Organization Closure-perceive broken figure as being complete or whole Proximity-nearness, group together objects that are near one another Similarity-group together objects that are similar in appearance
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Gestalt Organization 4) Continuity-perceive a series of points or lines as having unity 5) Common fate-perceive elements that move together as belonging together
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Top-Down Processing The use of contextual information or knowledge of a pattern in order to organize parts of the pattern Ex:puzzles Box picture=“top” Finding pieces=“top down process”
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Bottom-up Processing The organization of the parts of a pattern to recognize, or form an image of, the pattern they compose Start with bits and pieces of info and become aware of the pattern formed by the assembled pieces only after you have labored a while Ex: puzzles with the box picture
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Perception of Movement
1)Autokinetic effect-the tendency to perceive a stationary point of light in a dark room as moving 2) Stroboscopic motion-a visual illusion in which the perception of motion is generated by a series of stationary images presented in rapid succession (flip book, motion pictures)
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Perception of Movement
3) Phi phenomenon- the perception of movement as a result of sequential presentation of visual stimuli -a row of lights is switched on, then off, then the next row… -the on-off process is perceived as movement (Ex: electronic scoreboard baseball)
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Depth Perception Monocular cues:cues that can be perceived by one eye, to create an illusion of depth Perspective:a monocular cue for depth based on the convergence (coming together) of parallel lines as they recede into the distance
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Interposition A monocular cue for depth based on the fact that a nearby object obscures a more distant object behind it Same size but which one seems closer?
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Shadowing A monocular cue for depth based on the fact that opaque objects block light and produce shadows Shadows give a sense of 3-dimentionality
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Texture Gradient A monocular cue for depth based on the perception that closer objects appear to have rougher (more detailed) surfaces
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Motion Parallax A monocular cue for depth based on the perception that nearby objects appear to move more rapidly in relation to our own motion Mountains-move with us (greater distances) Trees, roadside markers-move rapidly
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Binocular Cues Stimuli suggestive of depth that involve simultaneous perception by both eyes Ex: close one eye and bring fingertips together Ex: roll up paper and you will see a hole in your hand
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Retinal disparity-difference in the image cast by an object on the retinas of the eyes as the object moves closer or farther away Ex: index finger to nose
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Constancy Color Constancy- objects retain color even though lighting conditions may alter their appearance Brightness-object just as bright even though lighting conditions changes its intensity Shape- object as being the same shape although the retinal image varies in shape as it rotates
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Visual illusions Spinning Circle Pg. 151-152 The Hering-Helmholtz
The Muller-Lyer illusion Ponzo illusion
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The Ganzfeld Contours are important Little sensory change can lead to:
Dizziness Fatigue “snow blindness”
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Vision and Balance Exercise: stand on one foot, then close your eyes, then try after you spin around a few times Maintaining balance depends on visual cues to some extent
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Hearing
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Pitch and Loudness The pitch of a sound is determined by its frequency, or the number of cycles per second as expressed in the unit Hertz (Hz). Hz=one cycle per second The greater the number of cycles per second (Hz), the higher the pitch of the sound (women vs. men)
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Loudness Amplitude:loudness of a sound that is determined by its height of sound waves Decibel (dB): a unit expressing the loudness of a sound (Sound waves of various frequencies and amplitudes)
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Loudness Tones (musical sounds)
Consonant:when a combination of tones are pleasant; in harmony Dissonant:incompatible; not harmonious, discordant
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White Noise Discordant sounds of many frequencies, often producing a lulling effect
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The Ear Diagram: Page 155-157 The Outer Ear The Middle Ear
The Inner Ear
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Deafness 28 million Americans have impaired hearing
2 million of them are deaf Conductive Deafness Sensorineural deafness
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Conductive Deafness The forms of deafness in which there is loss of conductions of sound through the middle ear Have high absolute thresholds for detection of sounds at all frequencies Elderly profit from hearing aids
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Sensorineural Deafness
The forms of deafness that result from damage to hair cells or the auditory nerve So called ringing sensation that follows after exposure to loud sounds means that hair cells are being damaged Ex: Rock concerts, shooting range
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Smell and Taste
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Smell Smell and taste are the chemical senses
With smell and taste, we sample molecules of the substance being sensed Humans are underprivileged when compared to dogs
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Smell Smell makes crucial contribution to the flavor of foods
Ex: If you did not have a sense of smell, then an onion and an apple would taste the same to you Detect odor of one-millionth of a milligram of vanilla in a liter of air
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Smell Odor: the characteristic of a substance that makes it perceptible to the sense of smell Odors detected by sites on receptor neurons in the olfactory membrane high in each nostril Olfactory: Having to do with the sense of smell
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Smell Olfactory nerve: the nerve that transmit information concerning odors from olfactory receptors to the brain
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Smell Mixtures of smell sensations help produce broad range of odors
Sense of smell adapts rapidly to odors even obnoxious ones (locker room, outhouse, second hand smoke, fumes) One odor can be masked by another (air fresheners)
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Taste -sour -salty -bitter
Dogs can perceive the taste quality of sweetness, as can pigs, but cats cannot 4 primary taste qualities: -sweet -sour -salty -bitter
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Taste Flavor of food involves taste but is more complex Apples and onions same taste qualities but their flavors differ greatly
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Taste Depends on its odor, texture, temperature as well as its taste
Flavor cont… Depends on its odor, texture, temperature as well as its taste
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Taste Cells Receptor cells that are sensitive to taste Located on taste buds
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Taste buds the sensory organs for taste. They contain taste cells and are located on the tongue 10,000 taste buds-located near the edges of tongue and the back of tongue
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Taste Buds Specialized a bit Sweetness: tip of tongue
Bitterness: back of tongue Sourness: along sides of the tongue Saltiness: overlaps the areas sensitive to sweetness and sourness
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Taste buds We all have different taste worlds Strong genetic component
By eating hot foods and scraping tongue, you regularly kill off many taste buds, Taste buds reproduce rapidly and completely renew once a week
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Taste buds Elderly complain their food has little or no taste-more likely to experience a decline in the sense of smell Older people experience the loss of flavor.
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The Skin Senses Touch Pressure Warmth Cool Pain
Skin discriminates among many kinds of sensations: Touch Pressure Warmth Cool Pain
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Touch and Pressure Sensory receptors at the roots of hair cells appear to fire in response to touching the surface of the skin “get the feel of”-touching fabric by running our hands over it. Sensation fade quickly if held still
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Touch and Pressure “Active touching”-involves reception of information that concerns not only touch but also pressure, temperature, and feedback from muscles
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Touch and Pressure Two-point threshold:the least distance by which two rods touching the skin must be separated before the person will report that there are two rods, not one, on 50% of occasions. Assess our sensitivity to pressure (fingertips, lips, noses, and cheeks are much more sensitive than our shoulders, thighs, and calves)
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Touch and Pressure Differential sensitivity occurs for 2 reasons:
Nerve endings are more densely packed in the fingertips and face than in other locations A greater amount of sensory cortex is devoted to the perception of sensations in the fingertips and face -sense of pressure, like the sense of touch, undergoes rather rapid adaptation
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Temperature Receptors for temperature are neurons beneath the skin
When skin temperature increases, receptors for warmth fire (same for cold receptors) Sensations of temperature are relative We adapt to differences in temperature (Ms. Yen’s classroom freezing classroom, pools, weather outside)
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Pain Pain is a signal that something is wrong in the body
Originates at the point of contact (stubbed toe) Pain message to the brain is initiated by the release of various chemicals: (Prostaglandins, bradykinin, mysterious chemical called P)
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Phantom Limb Pain The pain occurs in the absence of (present) tissue damage, but the pain itself is real enough (war veterans) Sometimes involves activation of nerves in the stump of missing limb Pain reflect activation of the neural circuits that store memories connected with the missing limb
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Kinesthesis The sense that informs us about the positions and motion of parts of our bodies
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