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Sensation and perception
6 Sensation and perception
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6 Definitions Sensation Perception
The detection of physical energy emitted or reflected by physical objects 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
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6 Ambiguous figure Colored surface can be either the outside front surface or the inside back surface. But not simultaneously both The brain can interpret the ambiguous cues in two different ways.
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Riddle of separate sensations
6 Riddle of separate sensations Sense receptors Specialized cells that convert physical energy into electrical energy that can be transmitted as nerve impulses to the brain
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Sensation and perception
6 Sensation and perception
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Specific nerve energies
6 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. Synesthesia A condition in which stimulation of one sense also evokes another
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6 Absolute threshold The smallest quantity of physical energy that can be reliably detected by an observer
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6 Absolute thresholds Vision Hearing Smell Touch Taste
A single candle flame from 30 miles on a clear night Hearing The tick of a watch from 20 feet in total quiet Smell One drop of perfume in a 6-room apartment Touch The wing of a bee on the cheek, dropped from 1 cm Taste One teaspoon of sugar in 2 gallons of water
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6 Difference threshold The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared Also called the Just Noticeable Difference (JND)
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Signal-detection theory
6 Signal-detection theory A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process
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Sensory adaptation and deprivation
6 Sensory adaptation and deprivation Adaptation The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious Prevents us from having to respond continuously to unimportant information Deprivation The absence of normal levels of sensory stimulation
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6 Sensory overload Over-stimulation of the senses
Can use selective attention to reduce sensory overload Selective attention: the focusing of attention on selected aspects of the environment and the blocking out of others
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6 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
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6 What we see Hue Brightness Saturation
Visual experience specified by color names and related to the wavelength of light Brightness Visual experience related to the amount of light emitted from or reflected by an object Saturation Visual experience related to the complexity of light waves
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6 What we see
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6 An eye on the world Cornea Lens Iris Pupil
Protects eye and bends light toward lens Lens Focuses on objects by changing shape Iris Controls amount of light that gets into eye Pupil Aperture through which light reaches the retina
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6 An eye on the world Retina Rods Cones
Neural tissue lining the back of the eyeball’s interior containing the receptors for vision Rods Visual receptors that respond to dim light Cones Visual receptors involved in color vision
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Structures of the retina
6 Structures of the retina
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6 Your turn You have a hard time locating your red car at night, in the poorly lit mall parking lot. Why? 1. Your rods are less sensitive to color in dim light. 2. Your cones, which detect color, do not function well in dim light. 3. Your ganglion cells receive insufficient overall stimulation to function. 4. Your rods, which detect color, do not function well in dim light.
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6 Your turn You have a hard time locating your red car at night, in the poorly lit mall parking lot. Why? 1. Your rods are less sensitive to color in dim light. 2. Your cones, which detect color, do not function well in dim light. 3. Your ganglion cells receive insufficient overall stimulation to function. 4. Your rods, which detect color, do not function well in dim light.
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The visual system is not a camera
6 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 cortical cells 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
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Huble and Wiesel’s experiment
6 Huble and Wiesel’s experiment
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6 Trichromatic theory Young (1802) and von Helmholtz (1852) both proposed that the eye detects 3 primary colors Red, blue, and green All other colors derived by combination
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Opponent-process theory
6 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.
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6 Afterimages
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6 Afterimages
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Test of color deficiency
6 Test of color deficiency
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6 Form perception Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.
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6 Gestalt principles Proximity Closure
Things close to one another are grouped together Closure The brain tends to fill in gaps to perceive complete forms
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6 Gestalt principles Similarity Continuity
Things that are alike are perceived together Continuity Seeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction.
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6 Your turn Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram? 1. Similarity 2. Proximity 3. Closure 4. Continuity
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6 Your turn Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram? 1. Similarity 2. Proximity 3. Closure 4. Continuity
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Depth and distance perception
6 Depth and distance perception Binocular cues: visual cues 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 right and left eyes
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Depth and distance perception
6 Depth and distance perception Monocular cues: visual cues that can be used by one eye
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The Müller-Lyer illusion
6 The Müller-Lyer illusion
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6 Color in context The way you perceive a color depends on the color surrounds.
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6 The Ames room A specially-built room that makes people seem to change size as they move around in it. The room is not a rectangle, as viewers assume it is. A single peephole prevents use of binocular depth cues.
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6 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
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6 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 inches in front of face.
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6 What we hear Loudness Pitch Timbre
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 The dimension of auditory experience related to the complexity of a pressure wave
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6 An ear on the world
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Auditory localization
6 Auditory localization Sounds from different directions are not identical as they arrive at left and right ears. Loudness Timing Phase The brain calculates a sound’s location by using these differences.
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6 Other senses Taste: savory sensations Smell: the sense of scents
Senses of the skin The mystery of pain The environment within
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Taste: savory sensations
6 Taste: savory sensations Papillae Knoblike elevations on the tongue, containing the taste buds Taste buds Nests of taste-receptor cells
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6 Taste buds 10,000 taste buds line the tongue and mouth
Receptors are down inside the “bud”. Children have more taste buds than adults.
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6 Four tastes Five basic tastes
Salty, sour, bitter, sweet, and umami Different people have different tastes based on: Genetics Culture Learning Food attractiveness
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Smell: The sense of scents
6 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.
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6 Olfactory system
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6 Sensitivity to touch
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Gate-control theory of pain
6 Gate-control theory of pain Experience of pain depends in part on whether the pain gets past a neurological “gate” in the spinal cord.
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Neuromatrix theory of pain
6 Neuromatrix theory of pain The matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.
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The environment within
6 The environment within Kinesthesis The sense of body position and movement of body parts Equilibrium The sense of balance Semicircular canals Sense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head
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Inborn abilities: The visual cliff
6 Inborn abilities: The visual cliff 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.
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6 Critical period If infants miss out on experiences during a crucial period of time, perception will be impaired. When adults who have been blind since birth have vision restored, they may not see well. Other senses such as hearing may be influenced similarly.
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Psychological and cultural influences
6 Psychological and cultural influences We are more likely to perceive something when we need it. What we believe can affect what we perceive. Emotions, such as fear, can influence perceptions of sensory information. Expectations based on previous experiences can influence perception. Perceptual set: a habitual way of perceiving, based on expectations All are influenced by culture.
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6 Perceptual set
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6 Priming A method used to insure unconscious processes, in which a person is exposed to information and is later tested to see whether the information affects behavior or performance on another task or in another situation Findings suggest simple primes influence perception, memory, thinking, and decision-making.
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Perception vs. persuasion
6 Perception vs. persuasion Although subliminal priming can influence judgments and preferences, research doesn’t support its success in major levels of persuasion.
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Extrasensory perception
6 Extrasensory perception ESP The ability to perceive something without ordinary sensory information Has not been scientifically demonstrated
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6 Parapsychology J. B. Rhine conducted many experiments on ESP using stimuli such as these. Rhine believed his evidence supported ESP, but his findings were flawed.
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