sensation & perception chapter4. sensation def:the stimulation of sensory receptors and the...
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Sensation & Perception
Chapter4
Sensation• Def:the stimulation of sensory
receptors and the transmission of sensory information to the central nervous system (brain and spinal cord)
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
Perception• Not mechanical but interpreted• Def: the process by which
sensations are organized into an inner representation of the world
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
Absolute Threshold
• The weakest amount of a stimulus that can be told apart from no stimulus at all
• Table 4.1 pg.126• Ex: TasteAbout 1 teaspoon of sugar dissolved in
2 gallons of water
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
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)
Signal-Detection Theory
• The view that the perception of sensory stimuli involves the interaction of physical, biological, and psychological factors
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
Signal-Detection Theory
• Psychological factors include:-motivation, expectations, learning-emphasizes the aspects of detecting and responding to signals• Ex: studying and baby’s cry
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
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
Desensitization• Becoming less sensitive to
ongoing stimulation• constant light appears to grow
dimmer• Live in city, become
desensitized to traffic sounds
Vision & Dimensions of Color
The Eye• Pages 131-135• Know the different parts of
the eye and their functions for the test
Rods and Cones• Photoreceptors in the retina• About 125 million rods and
6.5 million cones are distributed across the retina
Rods• Rod-shaped photoreceptors
that are sensitive only to the intensity of light• They allow us to see in black
and white
Cones• Cone-shaped photoreceptors
that transmit sensations of color• Provide color vision
Light Adaptation
• Dark adaptation:Dark adaptation: adjusting to lower adjusting to lower lightinglighting
• Movie theater:Movie theater:--ConesCones: permit perception of color, reach : permit perception of color, reach maximum adaptation to darkness in 10 maximum adaptation to darkness in 10 minutesminutes--RodsRods: allow perception of light and dark : allow perception of light and dark only, are more sensitive and continue to only, are more sensitive and continue to adapt to darkness for up to about 45 adapt to darkness for up to about 45 minutesminutes
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
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
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
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
Saturation
•Hue: adding black•Tint: adding white
Complementary•The colors across from one another on the color wheel•Red-green•Blue-yellow
Primary Colors• Colors that cannot be produced by mixing pigments of other hues
• Red• Blue• Yellow
Secondary• Colors derived by mixing primary colors• Orange: mixing (red/yellow)• Green: mixing (blue/yellow)• Purple: mixing (red/blue)
Tertiary• Colors derived by mixing primary and adjoining secondary colors
• Yellow-green• Bluish-purple
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
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…
Visual Perception
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
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)
Visual Perception• Relies on our knowledge,
expectations, and motivations• An active process by which
we interpret the world around us
• Meaningless splotches handout
Perceptual Organization
• The tendency to integrate perceptual elements into meaningful patterns
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
Gestalt Organization
1) Closure-perceive broken figure as being complete or whole
2) Proximity-nearness, group together objects that are near one another
3) Similarity-group together objects that are similar in appearance
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
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”
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
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)
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)
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
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?
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
Texture Gradient• A monocular cue for depth based on the perception that closer objects appear to have rougher (more detailed) surfaces
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
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
• 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
Constancy1) Color Constancy- objects retain
color even though lighting conditions may alter their appearance
2) Brightness-object just as bright even though lighting conditions changes its intensity
3) Shape- object as being the same shape although the retinal image varies in shape as it rotates
Visual illusions• Spinning Circle• Pg. 151-152• The Hering-Helmholtz• The Muller-Lyer illusion• Ponzo illusion
The Ganzfeld• Contours are important• Little sensory change can lead to:–Dizziness–Fatigue–“snow blindness”
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
Hearing
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)
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)
Loudness• Tones (musical sounds)• Consonant:when a
combination of tones are pleasant; in harmony• Dissonant:incompatible; not
harmonious, discordant
White Noise
•Discordant sounds of many frequencies, often producing a lulling effect
The Ear
Diagram: Page 155-157
1) The Outer Ear2) The Middle Ear3) The Inner Ear
Deafness
• 28 million Americans have impaired hearing• 2 million of them are deaf• Conductive Deafness• Sensorineural deafness
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
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
Smell and Taste
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
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
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
Smell• Olfactory nerve: the nerve that transmit information concerning odors from olfactory receptors to the brain
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)
Taste• Dogs can perceive the taste quality
of sweetness, as can pigs, but cats cannot
• 4 primary taste qualities:
-sweet-sour-salty-bitter
Taste
• Flavor of food involves taste but is more complex• Apples and onions same
taste qualities but their flavors differ greatly
Taste
• Flavor cont…
•Depends on its odor, texture, temperature as well as its taste
Taste Cells
•Receptor cells that are sensitive to taste•Located on taste buds
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
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
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
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.
The Skin Senses
• Skin discriminates among many kinds of sensations:
• Touch• Pressure• Warmth• Cool• Pain
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
Touch and Pressure
• “Active touching”-involves reception of information that concerns not only touch but also pressure, temperature, and feedback from muscles
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)
Touch and Pressure
• Differential sensitivity occurs for 2 reasons:
1) Nerve endings are more densely packed in the fingertips and face than in other locations
2) 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
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)
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)
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
Kinesthesis• The sense that informs us about the positions and motion of parts of our bodies