Download - Sensation
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Chapter 5
Sensation
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Sensation• Sensation
– a process by which our sensory receptors and nervous system receive and represent stimulus energy
• Perception– a process of organizing and
interpreting sensory information, enabling us to recognize meaningful objects and events
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Sensation• Bottom-Up Processing
– analysis that begins with the sense receptors and works up to the brain’s integration of sensory information
• Top-Down Processing– information processing guided by
higher-level mental processes– as when we construct perceptions
drawing on our experience and expectations
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Sensation- Basic Principles
• Psychophysics– study of the relationship between
physical characteristics of stimuli and our psychological experience of them
– Light- brightness– Sound- volume– Pressure- weight– Taste- sweetness
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Sensation- Thresholds
• Absolute Threshold – minimum stimulation needed to
detect a particular stimulus– usually defined as the stimulus
needed for detection 50% of the time• Difference Threshold
– minimum difference between two stimuli that a subject can detect 50% of the time
– just noticeable difference (JND)– increases with magnitude
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Sensation- Thresholds
• Signal Detection Theory– predicts how and when we detect the
presence of a faint stimulus (signal) amid background stimulation (noise)
– assumes that there is no single absolute threshold
– detection depends partly on person’s• experience• expectations• motivation• level of fatigue
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Sensation- Thresholds
• Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion– light intensity- 8%– weight- 2%– tone frequency- 0.3%
• Sensory adaptation- diminished sensitivity with constant stimulation
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Vision• Transduction- conversion of one form
of energy to another• Wavelength- the distance from the
peak of one wave to the peak of the next
• Hue- dimension of color determined by wavelength of light
• Intensity- amount of energy in a wave determined by amplitude– brightness– loudness
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Vision- Spectrum of Electromagnetic Energy
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Vision• Pupil- adjustable opening in the
center of the eye
• Iris- a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening
• Lens- transparent structure behind pupil that changes shape to focus images on the retina
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Vision
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Vision• Accommodation
– change in shape of lens– focus near objects
• Retina– inner surface of eye– light sensitive– contains rods and cones– layers of neurons– beginning of visual information
processing
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Vision• Acuity- the sharpness of vision• Nearsightedness
– nearby objects seen more clearly– lens focuses image of distant
objects in front of retina
• Farsightedness– faraway objects seen more clearly– lens focuses near objects behind
retina
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Retina’s Reaction to Light- Receptors
• Cones– near center of retina (fovea)– fine detail and color vision– daylight or well-lit conditions
• Rods– peripheral retina – detect black, white and gray– twilight or low light
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Retina’s Reaction to Light
• Optic nerve- nerve that carries neural impulses from the eye to the brain
• Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there
• Fovea- central point in the retina, around which the eye’s cones cluster
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Vision- ReceptorsReceptors in the Human Eye
Cones Rods
Number
Location in retina
Sensitivity in dim light
Color sensitive? Yes
Low
Center
6 million
No
High
Periphery
120 million
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Pathways from the Eyes to the Visual
Cortex
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Visual Information Processing
• Feature Detectors– neurons in the
visual cortex respond to specific features
– shape– angle– movement
Stimulus
Cell’s responses
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How the Brain Perceives
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Illusory Contours
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Visual Information Processing
• Parallel Processing– simultaneous processing of
several dimensions through multiple pathways
– color– motion– form– depth
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Visual Information Processing
• Trichromatic (three color) Theory– Young and Helmholtz– three different retinal color receptors
• red• green• blue
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Color-Deficient Vision
• People who suffer red-green blindness have trouble perceiving the number within the design
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Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable color vision
“ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black
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Audition– Audition
•the sense of hearing
– Frequency•the number of complete
wavelengths that pass a point in a given time
– Pitch•a tone’s highness or lowness•depends on frequency
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The Intensity of Some Common Sounds
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Audition- The Ear• Outer Ear
– Auditory Canal– Eardrum
• Middle Ear– hammer– anvil– stirrup
• Inner Ear– oval window– cochlea– basilar membrane– hair cells
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Audition• Place Theory
– the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated
• Frequency Theory– the theory that the rate of nerve
impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch
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Audition• Conduction Hearing Loss
– hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea
• Nerve Hearing Loss– hearing loss caused by damage
to the cochlea’s receptor cells or to the auditory nerve• Older people tend to hear low
frequencies well but suffer hearing loss for high frequencies
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Touch• Skin Sensations
– pressure• only skin
sensation with identifiable receptors
– warmth– cold– pain
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Pain• Gate-Control Theory
– theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain
– “gate” opened by the activity of pain signals traveling up small nerve fibers
– “gate” closed by activity in larger fibers or by information coming from the brain
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Taste• Taste Sensations
– sweet– sour– salty– bitter
• Sensory Interaction– the principle that one sense may
influence another– as when the smell of food influences its
taste
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Smell
Receptor cells inolfactory membrane
Nasal passage
Olfactorybulb
Olfactorynerve
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Body Position and Movement
• Kinesthesis– the system for sensing the
position and movement of individual body parts
• Vestibular Sense– the sense of body movement and
position– including the sense of balance