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Perception. Bottom-up processing. Detecting physical energy from the environment and encoding it as neural signals Traditionally this process is called “sensation.” Advocates assume that the mind constructs perceptions mechanically from raw sensations. Top-down processing.
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Bottom-up processing • Detecting physical energy from the environment and encoding it as neural signals • Traditionally this process is called “sensation.” • Advocates assume that the mind constructs perceptions mechanically from raw sensations.
Top-down processing • The idea that your experiences and expectations affect what you see • Traditionally known as “perception.” • Gestalt psychologists (“the whole is greater than the sum of its parts”) favored this approach. • Gestaltists think that perceptions can’t be understood by analyzing scenes into elements; you must look at the relation of elements to one another.
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Selective attention • At any moment, our awareness focuses on only a limited aspect of all that we experience. • Our five senses take in about 11,000,000 bits of information per second, but we only consciously process about 40.
Cocktail party effect • Another example of selective attention • The ability to tune into only one voice among many • We usually tune in to our own name or to a juicy bit of gossip that grabs our attention • Shows that the brain is constantly filtering out what’s important vs. what is trivial
Inattentional blindness http://www.youtube.com/watch?v=nkn3wRyb9Bk Failing to see something rather obvious because you’re busy attending to something else Example: Simons & Chabris (1999) gorilla-in-our-midst demonstration
Change blindness • Similar to inattentional blindness • If there’s a change in the environment, about 2/3 of people don’t notice it. • http://www.youtube.com/watch?v=vBPG_OBgTWg
Choice blindness • Sometimes people even forget what their own choices were and will even justify why they chose what they never chose in the first place. • http://www.youtube.com/watch?v=wRqyw-EwgTk
The pop-out phenomenon • Some things are too obvious to be ignored. • Contrast, novelty, stimulus intensity, color, and sudden change tend to capture our attention.
Figure-ground relationship • Our tendency to divide the perceptual world into two distinct parts—discrete figures and the background against which they stand out. • The figure has a definite shape and location in space; the ground has no shape, seems to continue behind the figure, and has no definite location.
Another example of figure-ground • Our attention can only focus on one figure at a time. Is this a young lady or an old one?
Making something meaningful out of sensations • How do we organize a figure into a meaningful form? • Basic features—color, movement, light/dark contrast—are processed instantly and automatically. • Our minds follow rules for grouping stimuli together (Gestalt psychologists). • Even infants use these rules. Some evidence, though, suggests they may be learned rather than innate. • The perceived whole is greater than the sum of its parts (a Gestalt idea).
Rules for grouping • Proximity: we group nearby figures together and perceive them as part of the same form. • Closure/connectedness: we tend to fill in minor gaps in forms that we perceive • Similarity: we group similar items together and perceive them as part of the same form • Continuity: we tend to group stimuli into forms that follow continuous lines or patternsor in the simplest way possible.
Depth perception • We somehow organize the 2-D images on our retinas into 3-D perceptions. This is depth perception. • This ability is partly innate. • Gibson & Walk (1960) placed 6-14 month-old infants on a visual cliff, and Moms tried to coax them onto the glass. Most babies refused to go.
Binocular cues • Require the interaction of both eyes • Convergence: a binocular cue; the degree to which eyes turn inward to focus on an object. Eyes move so they can both look at a visual scene. When objects are close, eyes turn to inward, and the change in muscle tension tells your brain you’re looking at a close object (experiment: Hold finger in front of face & move it inward). • Retinal disparity: Our two retinas receive slightly different images of the world. Brain compares these images, and the difference between them (retinal disparity) tells us the relative distance of different objects.
Retinal disparity and 3-D movies • The closer objects are, the further apart they are on the retina. • 3-D movies are shot by two cameras from slightly different angles. • When you wear the special glasses, each eye sees a slightly different view of the scene (left eye sees view from left camera; right eye sees view from the right camera), which creates an impression of depth.
Monocular cues: require only one eye • Interposition: if one object is placed between us and another object, we assume that it is closer. • Relative size: If we assume that 2 objects are similar in size, we perceive the one that casts the smaller retinal image as farther away. • Relative clarity: We assume that hazy objects are farther away than sharp, clear objects. • Texture gradient: A gradual change from a coarse, distinct texture to a fine, indistinct texture signals increasing distance. • Relative height: We perceive objects higher in our field of vision as farther away.
More monocular cues • Relative motion: As we move, objects that are actually stable may appear to move (looking at houses through the window of a bus). Nearer the object is to you, the faster it seems to move. • Linear perspective: Parallel lines (railroad tracks) appear to converge with distance. The more the lines converge, the greater the perceived distance. • Light and shadow: Nearby objects reflect more light to our eyes. Dimmer objects seem farther away. • Artists use monocular cues to convey depth perception.
Constancy Perceptual constancy: Perceiving objects as unchanging even as illumination and retinal images change. Size constancy: The tendency to perceive a physical object as having a constant size, even when the image it casts on the retina changes. Shape constancy: the perceived shape of an object doesn’t alter, even as the retinal image changes. Example: You recognize your friend walking down the street. As you get closer to her and see her from different angles, you still realize who she is.
Illusions • Instances in which perceptions yield false interpretations of physical reality • Two basic categories • Illusions of size • Illusions of shape or area
Why do illusions occur? • Usually have multiple causes, but there are two main ones. • Theory of misapplied constancy: when looking at illusions, we interpret certain cues as suggesting that some parts are farther away than others. The powerful tendency toward size constancy comes into play. • Learning: We rely on past experiences to tell us what’s usually true, but sometimes the rules change. Also, as we have more exposure to an illusion, its effect declines in magnitude.
Muller-Lyer Illusion • This is the classic version of this illusion, dating to 1889. • Which line is longer?
Explanation for Muller-Lyer • Although it’s been the subject of over 1250 scientific studies, scientists still debate its explanation. • It’s thought that learning plays a big role. • Our experience with corners of rooms works well in the 3-D world but can trip us up in a line drawing. • Rural Africans who do not live in an environment constructed of rectangular buildings are less vulnerable to the Muller-Lyer.
More about Ponzo • In this illusion, parallel lines appear to converge. (Called linear perspective) • The closer they are, the farther away (and bigger) you perceive an object between them to be • The yellow lines in the previous picture are actually the same length.
The Moon illusion • The moon looks up to 50% larger near the horizon than when high in the sky.
Explanation for the moon illusion • Scientists have wondered about it for 2200 years. • One reason: Cues to objects’ distances at the horizon make the moon behind them seem farther away than the moon high in the night sky, so the horizon moon seems larger. • If you take away the objects at the horizon and look at it through a paper tube, the moon immediately “shrinks” in size.
The Ames Room illusion explanation • An illusion of shape or area. • The Ames room appears normal and rectangular to a person peering into it, but it’s actually a trapezoid.
The illusion of the Arch • The Gateway Arch is actually as wide as it is tall. • It’s an illusion of size. The horizontal-vertical illusion stems from our tendency to perceive objects higher in our visual field as more distant.
Poggendorf Illusion • An illusion of shape. • A line disappears at an angle behind a solid figure, reappearing at the other side, at what seems to be the incorrect position.
Sensory Deprivation and Restoration • Does someone who was born blind and then gets his sight restored automatically know how to see? • No. Learning is involved. • People with restored vision can recognize colors and figure/ground relationships but lack perceptual constancy & can’t recognize by sight objects they knew by touch. • Appears to be a critical period in development for normal sensory and perceptual development.
Psi • Unusual processes of information or energy transfer that are currently unexplained in terms of known physical or biological mechanisms. • Includes ESP, which has 3 categories: • Telepathy --reading others’ thoughts • Clairvoyance --perceiving distant objects that don’t directly stimulate your sense organs) • Precognition—knowing what’s going to happen before it does Also includes psychokinesis—ability to move objects with the mind.
Is ESP/Psi real? • There are psychologists who study the paranormal. They’re called parapsychologists. • 96% of U.S. scientists are skeptical. • Gene Emery (2004) tracked psychic predictions for 26 years and found that virtually never have psychics anticipated any of the year’s headline events. • Psychic visions offered to police departments are no more accurate than guesses made by others.
More about ESP • Sometimes a psychic’s predictions are “retrofitted” to match events that have occurred (e.g., Nostradamus’s predictions) • By chance alone, there will be more than 1000 people a day who will think of someone and then 5 minutes later will learn of the person’s death.
Experimental evidence—or lack thereof • Thousands of experimental studies have consistently shown failures of evidence—or failures to replicate—that ESP exists. • Often when evidence is shown to exist, an alternative explanation is found—fraud, methdological problems, or normal sensory functioning. • The more controlled studies of psi are, the less evidence for it they have produced. • Another problem: the studies are often conducted by parapsychologists who firmly believe in psi’s existence.
A final problem for scientists and ESP • In order for ESP to be shown to exist, scientists would have to discard present-day scientific understanding that all aspects of our behavior must ultimately stem from biochemical events. • Scientists have no explanation for psychic phenomena; therefore, it doesn’t exist to them. Belief would require restructuring our view of our physical world.
Why do people still believe in ESP? • Psychologists believe that people still long for the magical. • Sometimes when people lose their religious beliefs, their belief in the occult, mysticism, and paranormal phenomena grows. They’re searching for some meaning to life.
