A.P. Psychology

Chapter 6

*Perception

*Perception

*We must select, organize, and interpret our sensations – a process called perception.

*We transform sensations into perceptions.

*We create meaning.

*Ex: a symphony

*Selective Attention*Perception comes to us moment by moment, one perception vanishing as the next appears.

*Selective attention means that at any moment we focus our awareness on only a limited aspect of all that we are capable of experiencing.*Ex: “Cocktail Party Effect” – the ability to attend selectively to only one voice among many.

*Moreover, if someone at a loud party audibly speaks your name, your attuned perceptual system may bring the voice to consciousness.

*At the level of conscious awareness, whatever has your attention pretty much has your undivided attention.

*It is true of the other senses as well.*From the immense array of visual stimuli constantly before us, we select just a few to process.

*Ex: BB game video

*Perceptual Illusions*Once we have attended to certain

stimuli, how do we organize them into meaningful perceptions?

*Illusions on page 240-241.

*Psychology’s emphasis on visual illusions reflects vision’s preeminence among our senses.

*When vision conflicts with other sensations, vision usually dominated – a phenomenon called VISUAL CAPTURE.

*EX: movie projector – sound comes from behind, but we perceive as coming from the screen.

*EX: virtual rides

*Form Perception*Figure-Ground*Our first perceptual task is to perceive any object, called the figure, as distinct from its surroundings, called the ground.*Ex: Voices at a party – the one you attend to is the

figure, all other parts are the ground.

*Ex: As you read these words, they are the figure, the blue slide is the ground.

*The figure-ground relationship continually reverses – but always we organize the stimulus into a figure seen against a ground.*Ex: vase or faces – which ever you are looking at is the

figure, the other the ground.

*Shows that the same stimulus can trigger more than one perception.

*However, if you don’t know it is reversible, it is not likely to reverse.

*Perceptual Organization*Gestalt – a German word meaning “whole”

*Gestalt psychologists described principles by which we organize our sensations into perceptions.

*See figure 6.6 (p. 244) – cube or circles with white lines?

*There is far more to perception than meets the senses.*Our brains do more than just merely register information about the world – we constantly filter sensory information and infer perceptions in ways that make sense to us.

* Form Perception

*Grouping – organizing the figure into a meaningful form

*Some basic features we process instantly and automatically – color, movement, and light-dark contrast.

*To bring order and form to these basic sensations, our minds follow certain rules for grouping stimuli together.

*These rules, identified by the Gestalt psychologists, illustrate their idea that the perceived whole differs from the sum of its parts.

*Usually, these grouping principles help us construct reality, but sometimes, they can lead us astray.

*Ex: Figure 6.7 (p. 244)

*Rules of Grouping (p. 244)*Proximity

*We group nearby figures together.

*We see not six separate lines, but three sets of two lines.

*Similarity

*Figures similar to each other we group together.

*We see the triangles and circles as vertical columns of similar shapes

*Continuity

*We perceive smooth, continuous patterns rather than discontinuous ones.

*Connectedness

*When they are uniform and linked, we perceive spots, lines, or areas as a single unit.

*Closure

*We fill in gaps to create a complete, whole object.

*We assume the circles are complete but partially blocked by the illusory triangle.

*Depth Perception*Two-dimensional images fall on our retinas, yet we somehow organize

three-dimensional perceptions.

*Seeing objects in three-dimensions is called depth perception and enables us to estimate their distance from us.

*Ex: We estimate distance of oncoming car or height of a house.

*This ability is partly innate.

*Visual Cliff experiment – see figure 6.8 (p. 245)

*Each species, by the time it is mobile, has the perceptual abilities it needs.

*Biological maturation predisposes our wariness of heights and experience amplifies it.

*How do we do it – with monocular and binocular cues.

*Binocular Cues

*Because our eyes are about 2 ½ inches apart, our retinas receive slightly different images of the world.

*When the brain compares these two images, the difference between them – retinal disparity – provides an important cue to the relative distance of different objects.*The disparity is smaller at greater distances.

*Try the finger sausage test.

*Another binocular cue to distance is convergence, a neuromuscular cue caused by the eyes’ greater inward turn when they view a near object.

*Monocular Cues

When looking at greater distances straight ahead, the retinal disparity is slight. At such distances, we rely on monocular cues.

Interposition

• If one object partially blocks our view of another, we perceive it as closer.

Relative Size

• If we assume that two objects are similar in size, we perceive the one that casts the smaller retinal image as farther away.

We perceive objects

higher in our field of vision as farther away.This

reverses above the horizon, as when we

perceive a higher bird as closer.

Relative Clarity Texture

Gradient

Relative Height

Relative motion (motion

parallax)

• As we move, objects that are actually stable may appear to move.

• The nearer an object is, the faster it seems to move.

• Objects beyond your fixation point seem to slow down as they get farther away.

• Your brain uses these speed and directions clues to compute the objects’ relative distances.

Linear perspective

• Parallel lines, such as railroad tracks, appear to converge with distance.

• The more they converge, the greater their perceived distance.

• Can contribute to railroad crossing accidents by leading people to overestimate its distance – the massive size of the train makes it appear to move slower than it actually is.

Light and shadow

•Nearby objects reflect more light to our eyes, thus, given two identical objects, the dimmer one seems farther away (can cause accidents also)

• Shading produces a sense of depth consistent with the assumed light source – our brains follow a simple rule: Assume that light comes from above. (invert p. 248)

* Motion Perception

*Our brain computes motion based partly on its assumption that shrinking objects are retreating (not getting smaller) and enlarging objects are approaching.

*Skilled baseball, softball, and cricket players perceive motion with astounding speed and accuracy.

*The brain will also interpret a rapid series of slightly varying images as movement – stroboscopic movement (used by film animators).

*Marquees and holiday lights sometimes create another illusion of movement using the phi phenomenon.

*Two adjacent stationary lights blink on and off in quick succession – we perceive a single light moving back and forth between them.

*Perceptual Constancy*First, we perceive objects as having a distinct form, location, and perhaps motion.

*Now we have to recognize the object without being deceived by changes in its size, shape, brightness, or color.

*Retinal constancy enables us to perceive an object as unchanging even though the stimuli we receive from it change.*Thus, we can identify things regardless of the angle, distance, and illumination by which we view them.

* Shape and Size Constancies

*Size Constancy

•Sometimes an object whose actual shape cannot change seems to change shape with the angle of our view. (picture p. 250)

•More often, thanks to shape constancy, we perceive the form of familiar objects as constant even while our retinal images of them change (open door).

• Thanks to size constancy, we perceive objects as having a constant size, even while our distance from them varies (car far away looks small, but we know it can still carry people).

• Perceiving an object’s distance gives us cues to its size.

• Knowing its general size provides us with cues to its distance.

Shape Constancy

*Size-Distance Relationship*Given the perceived distance of an object and the size of its image on our retinas, we instantly and unconsciously infer the object’s size. (See figure 6.14 – p. 251)

*This interplay helps explain several well-known illusions:*Why does the moon look up to 50% larger near the bottom of the

horizon than when high in the sky (moon illusion – p. 251)

*We perceive the work not only as it is, but as we are

*Our occasional misperceptions reveal the workings of our normally effective perceptual processes.

*Using distance cues to assess perceived size triggers illusions only if we aren’t familiar with the object or if the distance cues are misleading.

* Lightness Constancy

*We perceive an object as having a constant lightness even while its illumination varies.

*A black piece of paper in sunlight still looks black, because it reflects much less light than the objects around it.

*View it through a tube where only black is showing, and it may look gray.

*Perceived lightness depends on relative luminance – the amount of light an object reflects relative to its surroundings.

*Perceived lightness stays roughly constant, given an unchanging context, but what happens when the surrounding context changes?

* Perception and Language

*Listening to an unfamiliar language, we have trouble hearing where one word stops and the next one begins.

*Listening to our own language, we automatically hear distinct words.

*This is a form of perceptual organization – but it is more, for we organize a string of letters – THED0GATEMEAT – into words that make sense.*“The do gate me at.”

*“The dog ate meat”

*This process involves not only organization but interpretation—discerning meaning in what we perceive.

* Perceptual Interpretation

*Perceptual abilities – is it nature or nurture?

*We come equipped to process sensory information.

*But John Locke argued that through our experiences, we also learn to perceive the world.

*So, how important is experience?

* Sensory Deprivation and Restored Vision

*Question to John Locke – born blind taught by touch; now as adult, he can see – would he distinguish between a cube and a sphere? Locke said no, because he had not learned to SEE the difference.

*Theory has been put to the test in modern day, and has been proven correct.

*Blind early in life – cortical cells do not develop normal connections.

*Blind after early childhood – then regain sight – return to normal vision.

*Indicates a “critical period” for normal sensory and perceptual development.

* Perceptual Adaptation

*New glasses – slightly disoriented, maybe dizzy – fine in a day or two

*Glasses that shift objects 40 degrees to the left – can you adapt?

*Yes – at first you would be off when throwing a ball or shaking a hand.

*In a short time, your accuracy would return.

*More radical pair of glasses – turns the world upside down – can you adapt?

*Fish and frogs cannot.

*Kittens, monkeys, and humans can. (video clip)

*Experiment showed people could eventually ride a motorcycle, ski the Alps, and fly an airplane (I’m not flying in it!).

*Perceptual Set*To see is to believe – to believe is to see!

*Our experiences, assumptions, and expectations may give us a perceptual set, or mental predisposition, that greatly influences what we perceive. (see figures 258-259)

*Once we have formed a wrong idea about reality, we have more difficulty seeing the truth.

*Our perceptual set can influence what we hear as well as what we see.*Ex: Disney movies with subliminal sex messages.

*Ex: Little Miss Muffet sat on a tuffet, eating her curtains away.

*Ex: The pilot said “cheer up” to the co-pilot, who thought he said “gear up” and lifted the wheels of the plane before they had left the ground.

* What determines our perceptual set?

*Through experience we form concepts (schemas) that organize and interpret unfamiliar information.

*Our schemas influence how we interpret ambiguous sensations with top-down processing.

*Confronted with ambiguous stimuli, we may apply different schemas.

*To 3 & 4 year olds, faces are more important than bodies (drawing, p. 258). By age 8, schemas for bodies become more elaborate.

*Our schemas for faces prime us to see facial patterns in cartoonists’ caricatures. (see fig. 259)

*Context Effects

*A given stimulus may trigger radically different perceptions, partly because of our differing schemas, but also because of immediate context.

*Ex: “eel is on the wagon” or “eel is on the orange” – the context creates an expectation.

*Ex: Did the speaker say “cults and sects” or “cults and sex”? We discern the meaning from the surrounding words.

*Directors often evoke emotion in an audience by defining a context in which viewers interpret an actor’s expressions.

*Play sad music and then say the word “morning” – people may interpret it as “mourning.”

*Can include stereotypes – like gender or culture

Cults

and

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s

*Is there ESP?

*Media Overflow:

*Paranormal TV

*Psychic wonders

*Parapsychologists – those who study paranormal occurrences

*Some are astonished at what people can do.

*Some (96% of scientists in the NAS) are skeptical

*If ESP is real, we would need to overturn the scientific understanding that we are creatures whose minds are tied to our physical brains and whose perceptual experiences of the world are built of sensations.

*Let’s evaluate claims for ESP:

*Claims of ESP

*Claims of paranormal phenomena include astrological predictions, psychic healing, reincarnation, communication with the dead, and out-of-body experiences.

*Of these, the most respectable, testable, and (for perception) relevant claims are for three varieties of ESP:

*Telepathy – mind-to-mind communication (one person sending thoughts to another or perceiving another’s thoughts).

*Clairvoyance – perceiving remote events, such as sensing that a friend’s house is on fire.

*Precognition – perceiving future events, such as a political leader’s death or a porting event’s outcome.

*Closely linked is psychokinesis – mind over matter – such as levitating a table or influencing the role of a die.