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©2002 Prentice Hall
Sensation and Perception
©2002 Prentice Hall
Sensation and Perception
• Our Sensational Senses
• Vision
• Hearing
• Other Senses
• Perceptual Powers: Origins and Influences
• Puzzles of Perception
©2002 Prentice Hall
Sensation and Perception
• Sensation: The detection of physical energy emitted or reflected by physical objects; it occurs when energy in the external environment or the body stimulates receptors in the sense organs.
• Perception: The process by which the brain organizes and interprets sensory information.
©2002 Prentice Hall
Ambiguous Figure
• Colored surface can be either the outside front surface or the inside back surface– Cannot simultaneously
be both
• Brain can interpret the ambiguous cues two different ways
©2002 Prentice Hall
Our Sensational Senses
The Riddle of Separate Sensations
Measuring the Senses
Sensory Adaptations
Sensory Overload
©2002 Prentice Hall
The Riddle of Separate Sensations
• Sense Receptors: Specialized neurons that convert physical energy from the environment or the body into electrical energy that can be transmitted as nerve impulses to the brain.
• Doctrine of Specific Nerve Energies: Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.
©2002 Prentice Hall
Measuring the Senses
• Absolute Threshold– The smallest quantity of physical energy that
can be reliably detected by an observer
• Difference Threshold– The smallest difference in stimulation that can
be reliably detected by an observer when two stimuli are compared; also called Just Noticeable Difference (JND).
©2002 Prentice Hall
Absolute Sensory Thresholds
• Vision: A single candle flame from 30 miles on a dark, clear night
• Hearing: The tick of a watch from 20 feet in total quiet
• Smell: 1 drop of perfume in a 3-room apartment• Touch: The wing of a bee on your cheek, dropped
from 1 cm• Taste: 1 tsp. Sugar in 2 gal. water
©2002 Prentice Hall
Signal Detection Theory
Stimulus is Present Stimulus is Absent
Response: “Present” Hit False
AlarmResponse: “Absent” Miss Correct
Rejection
©2002 Prentice Hall
Sensory Adaptations
• Sensory Adaptation: The reduction or disappearance of sensory responsiveness that occurs when stimulation is unchanging or repetitious.
• Sensory Deprivation: The absence of normal levels of sensory stimulation.
©2002 Prentice Hall
Sensory Overload
• Selective Attention: The focusing of attention on selected aspects of the environment and the blocking out of others.
©2002 Prentice Hall
Vision
What We See
An Eye on the World
Why the Visual System is Not a Camera
How We See Colors
Constructing the Visual World
©2002 Prentice Hall
What We See• Hue: The dimension of visual experience
specified by color names and related to the wavelength of light.
• Saturation: Vividness or purity of color; the dimension of visual experience related to the complexity of light waves.
• Brightness: Lightness and luminance; the dimension of visual experience related to the amount of light emitted from or reflected by an object.
©2002 Prentice Hall
An Eye on the World
• Retina: Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.
• Rods: Visual receptors that respond to dim light.
• Cones: Visual receptors involved in color vision. Most humans have 3 types of cones.
• Dark Adaptation: The process by which visual receptors become maximally sensitive to light.
©2002 Prentice Hall
Structures of the Human Eye
©2002 Prentice Hall
Structures of the Retina
©2002 Prentice Hall
The Visual System is Not a Camera
• Much visual processing is done in the brain.– Some cortical cells respond to lines in specific
orientations (e.g. horizontal)– Other cells in the cortex respond to other
shapes (e.g., bulls-eyes, spirals, faces)
• Feature-detectors: Cells in the visual cortex that are sensitive to specific features of the environment.
©2002 Prentice Hall
How We See Colors
• Trichromatic Theory
• Opponent Process Theory
©2002 Prentice Hall
Trichromatic Theory
• T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors– red, blue, & green
• All other colors can be derived by combining these three
©2002 Prentice Hall
Opponent-Process Theory
• A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic.
• Opponent-Process cells are inhibited by a color, and have a burst of activity when it is removed.
VS
VS
VS
Afterimages
©2002 Prentice Hall
Constructing the Visual World
• Form Perception
• Depth and Distance Perception
• Visual Constancies: When Seeing is Believing
• Visual Illusions: When Seeing is Misleading
©2002 Prentice Hall
Gestalt Principles• Gestalt principles describe the brain’s
organization of sensory building blocks into meaningful units and patterns.– Proximity– Closure– Similarity– Continuity
©2002 Prentice Hall
Depth and Distance Perception
• Binocular Cues: Visual cues to depth or distance that require the use of both eyes.– Convergence: Turning inward of the eyes,
which occurs when they focus on a nearby object
– Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.
• Monocular Cues: Visual cues to depth or distance that can be used by one eye alone.
©2002 Prentice Hall
Visual Constancies
• The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce.– Shape constancy– Location constancy– Size constancy– Brightness constancy– Color constancy
©2002 Prentice Hall
Visual Illusions
• Illusions are valuable in understanding perception because they are systematic errors.– Illusions provide hints about perceptual strategies
• In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.
©2002 Prentice Hall
Fooling the Eye
• The cats in (a) are the same size• The diagonal lines in (b) are parallel• You can create a “floating fingertip frankfurter”
by holding hands as shown, 5-10” in front of face.
©2002 Prentice Hall
Hearing
What We Hear
An Ear on the World
Constructing the Auditory World
©2002 Prentice Hall
What We Hear
• Loudness: The dimension of auditory experience related to the intensity of a pressure wave.
• Pitch: The dimension of auditory experience related to the frequency of a pressure wave.
• Timbre (pronounced “TAM-bur”): The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.
©2002 Prentice Hall
An Ear on the World
©2002 Prentice Hall
Other Senses
Taste: Savory Sensations
Smell: The Sense of Scents
Senses of the Skin
The Mystery of Pain
The Environment Within
©2002 Prentice Hall
Taste: Savory Sensations
• Papillae: Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).
• Taste buds: Nests of taste-receptor cells.
©2002 Prentice Hall
Smell: The Sense of Scents
• Airborne chemical molecules enter the nose and circulate through the nasal cavity.– Vapors can also enter through the mouth and pass into nasal
cavity.
• Receptors on the roof of the nasal cavity detect these molecules.
©2002 Prentice Hall
Gate-Control Theory of Pain
• Experience of pain depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.
©2002 Prentice Hall
Neuromatrix Theory of Pain
• Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.
©2002 Prentice Hall
The Environment Within
• Kinesthesis: The sense of body position and movement of body parts; also called kinesthesia.
• Equilibrium: The sense of balance.
• Semicircular Canals: Sense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head.
©2002 Prentice Hall
Perceptual Powers: Origins and Influences
Inborn Abilities and Perceptual Lessons
Psychological and Cultural Influences on Perception
©2002 Prentice Hall
The Visual Cliff
• Devised by Eleanor Gibson and Richard Walk to test depth perception
• Glass surface, with checkerboard underneath at different heights– Visual illusion of a cliff– Baby can’t fall
• Mom stands across the gap• Babies show increased attention
over deep side at age 2 months, but aren’t afraid until about the age they can crawl
©2002 Prentice Hall
Psychological and Cultural Influences on Perception
• Needs
• Emotions
• Expectations– Perceptual Set: A habitual way of perceiving,
based on expectations.
• Beliefs
©2002 Prentice Hall
Puzzles of Perception
Subliminal Perception
Extrasensory Perception: Reality or Illusion?
©2002 Prentice Hall
Extrasensory Perception
• Extrasensory Perception (ESP):– The ability to perceive something without
ordinary sensory information– This has not been scientifically demonstrated
• Three types of ESP:– Telepathy – Mind-to-mind communication– Clairvoyance – Perception of remote events– Precognition – Ability to see future events
©2002 Prentice Hall
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