Sensation and Perception Chapter 6 Sensation Perception How

Sensation and Perception Chapter 6

Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organize, and interpret our sensations, the process is called perception.

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A. ”

Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT

Making Sense of Complexity Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes, ” Bev Doolittle

Sensing the World Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them. Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet

Thresholds Proportion of “Yes” Responses 0. 00 0. 50 1. 00 Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. 0 5 10 15 20 Stimulus Intensity (lumens) 25

Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock

Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Put a band aid on your arm and after awhile you don’t sense it.

Both Photos: Thomas Eisner The Stimulus Input: Light Energy Visible Spectrum

Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next.

Wavelength (Hue) Violet Indigo 400 nm Short wavelengths Blue Green Yellow Orange Red 700 nm Long wavelengths Different wavelengths of light result in different colors.

Intensity (Brightness) Intensity: Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened. ”

The Eye

Parts of the eye 1. 2. 3. 4. Cornea: Transparent tissue where light enters the eye. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses the light rays on the retina. Retina: Contains sensory receptors that process visual information and sends it to the brain.

The Lens: Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

Retina: The lightsensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.

Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. Fovea: Central point in the retina around which the eye’s cones cluster. http: //www. bergen. org

Test your Blind Spot Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

Photoreceptors E. R. Lewis, Y. Y. Zeevi, F. S Werblin, 1969

Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which converge to form the optic nerve.

Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.

Feature Detection Ross Kinnaird/ Allsport/ Getty Images Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement.

Shape Detection Ishai, Ungerleider, Martin and Haxby/ NIMH Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

Visual Information Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

From Sensation to Recognition

Color Vision Trichromatic theory: Young and von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors. Standard stimulus Comparison stimulus Max Medium Low Blue Green Red

Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test

Hearing: The Stimulus Input -Sound Waves Sound waves are compressing and expanding air molecules.

The Ear Dr. Fred Hossler/ Visuals Unlimited

The Ear Outer Ear: Collects and sends sounds to the eardrum. Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window. Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

Intensity (Loudness): Amount of energy in a wave, determined by the amplitude, relates to the perceived loudness.

Loudness of Sound Richard Kaylin/ Stone/ Getty Images 120 d. B 70 d. B

Frequency (Pitch) Frequency (pitch): The dimension of frequency determined by the wavelength of sound. Wavelength: The distance from the peak of one wave to the peak of the next.

Localization of Sounds Because we have two ears, sounds that reach one ear faster than the other ear cause us to localize the sound.

Localization of Sound 1. Intensity differences 2. Time differences as small as 1/100, 000 of a second can cause us to localize sound. The head acts as a “shadow” or partial sound barrier.

Touch Bruce Ayers/ Stone/ Getty Images The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain.

Skin Senses Only pressure has identifiable receptors. All other skin sensations are variations of pressure, warmth, cold and pain. Pressure Burning hot Vibration Cold, warmth and pain

Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain. AP Photo/ Stephen Morton Ashley Blocker (right) feels neither pain nor extreme hot or cold.

Biopsychosocial Influences

Gate-Control Theory Melzack and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed. Gary Comer/ Phototake. USA. com

Taste Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”. Sweet Sour Salty Bitter Umami (Fresh Chicken)

Sensory Interaction When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor.

Smell Like taste, smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. Unlike taste, there are many different forms of smell.

Smell and Memories The brain region for smell (in red) is closely connected with the brain regions involved with memory (limbic system). That is why strong memories are made through the sense of smell.

Perceptual Organization How do we form meaningful perceptions from sensory information? We organize it. Gestalt psychologists showed that a figure formed a “whole” different than its surroundings.

Form Perception Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Time Savings Suggestion, © 2003 Roger Sheperd.

Grouping After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using grouping rules.

Grouping & Reality Although grouping principles usually help us construct reality, they may occasionally lead us astray. Both photos by Walter Wick. Reprinted from GAMES Magazine. . © 1983 PCS Games Limited Partnership

Depth Perception Innervisions Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception. Visual Cliff

Binocular Cues Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in the inset.

Monocular Cues Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away.

Monocular Cues Interposition: Objects that occlude (block) other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli.

Monocular Cues Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower. Image courtesy of Shaun P. Vecera, Ph. D. , adapted from stimuli that appered in Vecrera et al. , 2002

Monocular Cues Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction.

Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance. © The New Yorker Collection, 2002, Jack Ziegler from cartoonbank. com. All rights reserved.

Monocular Cues Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away. From “Perceiving Shape From Shading” by Vilayaur S. Ramachandran. © 1988 by Scientific American, Inc. All rights reserved.

Color Constancy Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object. Color Constancy

Size-Distance Relationship The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues. Alan Choisnet/ The Image Bank From Shepard, 1990

Size-Distance Relationship Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the two corners of the room. Both photos from S. Schwartzenberg/ The Exploratorium

Ames Room The Ames room is designed to demonstrate the sizedistance illusion.

Co ur tes y Ed wa rd Ad els on Lightness Constancy The color and brightness of square A and B are the same.

Sensory Deprivation & Restored Vision After cataract surgery, blind adults were able to regain sight. These individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle and a triangle (Von Senden, 1932).

Facial Recognition Courtesy of Richard Le. Grand After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed.

Sensory Deprivation Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars. Blakemore & Cooper (1970)

Perceptual Set A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures. From Shepard, 1990.

Perceptual Set Other examples of perceptual set. Dick Ruhl Frank Searle, photo Adams/ Corbis-Sygma (a) Loch ness monster or a tree trunk; (b) Flying saucers or clouds?

Context Effects Context can radically alter perception. Is the “magician cabinet” on the floor or hanging from the ceiling?

Cultural Context instilled by culture also alters perception. To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree.

Perception Revisited Is perception innate or acquired?