Sensation and perception - Cabrillo Collegecreyes/classes/SensPerception_Vision... ·...
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3/9/14 1 Sensation and perception 6 Definitions Sensation 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-Bottum up Perception The process by which the brain organizes and interprets sensory information-Top Down 6
Transcript of Sensation and perception - Cabrillo Collegecreyes/classes/SensPerception_Vision... ·...
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Sensation and perception
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Definitions Sensation 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-Bottum up
Perception The process by which the brain organizes and interprets sensory information-Top Down
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Perceiving Our World
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Translation of information into sensory experience.
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Transduction
Transduction: Translation of information from the environment into neural signals
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Specific nerve energies Different sensory modalities exist because signals received by the sense organs (eyes etc..) stimulate different nerve pathways leading to different areas of the brain.
Synesthesia A condition in which stimulation of one sense (hearing) also evokes another (vision)
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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. To some degree, Our response depends on our expectations and our interpretations.
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Sensory overload
Over-stimulation of the senses
Can use selective attention to reduce sensory overload. The “cocktail party phenomenon”
Selective attention: the focusing of attention on selected aspects of the environment and the blocking out of others. May also cause innattentional blindness
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What we see
Hue 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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What we see
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An eye on the world
Cornea 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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An eye on the world
Retina 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. Do not respond well in dim light. On reason it might be hard to find a red car in a dark parking lot.
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Structures of the retina
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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 1981 Nobel Prize
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How we see colors: 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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Trichromacy Theory
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How Does Sensation Lead to Perception? How Do We See? How Do We Hear? How Do We Feel Body Position,
Touch, Temperature, and Pain? How Do We Process Smells
and Tastes?
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Color in context 6
The way you perceive a color depends on the color surrounds.
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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Afterimages 6
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Test of color deficiency
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Form perception
Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.
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Gestalt principles Proximity Things close to one another are grouped together
Closure The brain tends to fill in gaps to perceive complete forms
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Gestalt principles Similarity 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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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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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
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
Monocular cues: visual cues that can be used by one eye
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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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The Müller-Lyer illusion
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The Ames Room
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How Does Sensation Lead to Perception? How Do We See? How Do We Hear? How Do We Feel Body Position,
Touch, Temperature, and Pain? How Do We Process Smells
and Tastes?
Click on play bu.on to launch video in QuickTime player.
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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Have you been to the Mystery Spot? SPOILER WARNING: :-)
Habituation to a steep gradient Similar to an Ames room.
See article on my site.
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Critical periods
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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Psych-socio-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. “Hello Walter!” vs. Shallow Water. Perceptual set: a habitual way of perceiving, based on expectations
All are influenced by culture. Rural Africans are less susceptible to the Muller-Lyer illusion because they live in a less “carpentered world” (round huts)
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ESP or Extrasensory perception: The field of Parapsychology ESP - (telepathy, precognition) The ability to perceive something without ordinary sensory information. Has been studied extensively but studies have been poorly designed with inadequate precautions against fraud. After an exhaustive review, the National Research Council Concluded that there was “No scientific justification….for the existence of parapsychological phenomena”.
BUT, the issue isn’t gone is it? Many people really really WANT to believe in ESP. Perhaps for some good reasons, discussed next week. Consider the story of James Randi (The Amazing Randi), Dr. Andrew Weil, and Uri Geller….
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