CH6: Perception

8/8/2019 CH6: Perception

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Andrew Lay

AP Psychology

CH6: Perception

- To construct the outside world inside our heads we detect physical energy from the

environment and encode it as neural signals: Sensation

-

We must also select, organize, and interpret our sensations: PerceptionI. Selective Attention

- Perceptions come to us moment by moment, one vanishing as the other appears (i.e. Necker’s cube)

- Selective Attention: The focusing of conscious awareness on a particular stimulus

o Cocktail party effect: The ability to focus on only one voice among many

If focusing on voice in right ear, one will not remember what the voice inthe left said, only the person’s gender and loudness

- Stimuli that we do not notice can affect us (these stimuli are not subliminal, just

unnoticed due to attention)

o Experiment: Women listened through headphones to a prose passage played in

one ear and music in the other and were asked to repeat the words out loud andcheck them against a written transcript. The women did not recognize the songs,

but when asked which songs they preferred, they chose the ones played when they

were listening to the prose.II. Perceptual Illusions

o Perceptual illusions reveal the ways we normally organize and interpret our

senses

o Visual Capture: The tendency for vision to dominate the other senses

When the sound of a movie comes from a projector behind us, we perceiveit as coming from the screen, where we see the actors talking

III. Perceptual Organization

-Gestalt: an organized wholeGestalt psychologists emphasize our tendency to integrate pieces of information into meaningful wholes

o Organize sensations into perceptions

Involves both bottom-up and top-down processing: Sensation and

perception are a continuous process in both directions- Form Perception

o Figure and Ground

Figure-Ground: The organization of the visual field into objects (the figures) that stand out from their surroundings (the ground )

- Is reversible in some images: can trigger more than one perception

o Grouping

Grouping: The perceptual tendency to organize stimuli into coherent

groups- Gives order and form to the figure

Gestalt psychologists have identified several rules

- Proximity: Group nearby figures together (i.e. seeing 3 sets of twolines, not six separate lines)



- Similarity: Figures similar to each other we group together (i.e. see

circles and triangles and vertical columns of similar shapes, nothorizontal rows of dissimilar shapes)

- Continuity: We perceive smooth, continuous patterns rather than

discontinuous ones. (i.e. Sin graph not a series of alternate

semicircles but two lines, one wavy, one straight)- 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. (i.e.

We assume that circles in figure are complete but are partially

blocked by an (illusory) triangle)

- While these grouping principles help us construct reality, they can

also lead us astray (i.e. neon worm—closure)- Depth Perception

o Depth Perception: The ability to see objects in three dimensions although the

images that strike the retina are two-dimensional; allows us to judge distance

o

Visual Cliff: A laboratory device for testing depth perception in infants and younganimals

Demonstrates depth perception is partly innate: Infants, young kittens, andday old goats would not venture onto the glass

o Biological maturation predisposes our wariness of heights, while experience

amplifies it

Children w/ walker more scared of heights

o Binocular Cues: Depth cues, such as retinal disparity and convergence that

depend on the use of two eyes

o Monocular Cues: Distance cues, such as linear perspective and overlap, available

to either eye alone

o Binocular Cues Retinal Disparity: Binocular cue for perceiving depth; The greater the

disparity (difference) between the two images the retina receives of anobject, the closer the object is to the viewer

- When you hold your finger directly in front of your nose, your

retinas receive quite different views, when you move it outward,the disparity becomes smaller

- Concept used in 3-D movie making and stereograms

Convergence: Binocular cue for perceiving depth; the extent to which theeyes converge inward when looking at an object

- The eyes turn more greatly inward when focusing on a closer

object (brain knows difference between focusing on book andsomething across the room)

o Monocular Cues

We rely on monocular cues when objects are at a distance (disparity is

slight)

- 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

- Relative Clarity: Because light from distant objects passes through

more atmosphere, we perceive hazy objects as farther away than

sharp, clear objects (i.e. effect of fog on judging distance)- Texture Gradient: A gradual change from a coarse, distinct texture

to a fine, indistinct texture signals increasing distance. Objects far away appear smaller and more densely packed.

- Relative Height: 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)

o May contribute to the illusion that vertical dimensions are

longer than identical horizontal dimensions (i.e. the

gateway arch)

- Relative Motion (motion parallax): As we move, objects that are

stable may appear to move. The nearer an object is, the faster itseems to move (as when riding in a train). Brain uses speed anddirection clues to compute distance

- Linear Perspective: Parallel lines, such as railroad tracks, appear to

converge with distance. The more the lines converge, the greater their perceive distance. (can lead to rail accidents)

- Light and Shadow: Nearby objects reflect more light to our eyes.

Dimmer objects seem farther away. (can also lead to accidents)

o Shading produces a sense of depth consistent with the light

source (used in illustrations)

- Motion Perception

o

We are by no means perfect at perceiving motion Large objects appear to be moving slower than smaller objects moving at

the same speed (can cause car-train accidents)

The brain computes motion based largely on its assumption that objects

that are shrinking are retreating and objects that are growing are

approaching

Illusions of motion

- Stroboscopic movement: The phenomenon that allows one to perceive motion in animations and motion pictures

- Phi Phenomenon: An illusion of movement created when two or

more adjacent lights blink on and off in succession (i.e. in

Christmas lights)- Perceptual Constancy

o Perceptual Constancy: Perceiving objects as unchanging (having consistent

lightness, color, shape, and size) even as illumination and retinal images change

Due to recognition in the brain

o Shape and Size Constancies

Shape constancy: We perceive the form of familiar objects as constant

even while our retinal images of them change (door always door)



Size Constancy: We perceive objects as having a constant size (car always

car)

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

sizeo Concept for illusions: If two objects cast the same size

retinal image, but one appears farther away, the farther

away one is perceived as being larger (messing w/ distance

cues)

Muller-Lyer illusion: length of line between open

arrows appears longer than length of line between

closed arrows (related to the way our depth perception behaves in the three-dimensional

worldticket booth example)

Girls in messed-up room

o Lightness Constancy Lightness constancy: we perceive an object as having constant lightness

even while its illumination varies

- Black paper in sunlight reflects more light than does white paper indoors

- Relies on relative luminance

- Perceived lightness changes with context

- Perceptual organization applies to other senses too

o Organize a clocks clicks into patterns

IV. Perceptual Interpretation- Sensory Deprivation and Restored Vision

o Evidence suggests that there is a critical period for normal sensory and perceptual

development

When cataracts were removed in human patients, they could distinguishfigure and ground but could not recognize shapes they could by touch

Kittens razed without exposure to horizontal lines had difficulty

perceiving them

- Perceptual Adaptation

o Perceptual Adaptation: In vision, the ability to adjust to an artificially displaced or

even inverted visual field

Kittens, monkeys, and humans can adapt to eyewear that inverts the world

after a short period of struggle

quickly learn to coordinate their movements

- Perceptual Set

o Perceptual Set: A mental predisposition to perceive one thing and not another

Loch Ness Monster (log), face on moon (craters), UFOs

People perceive evil messages while listening to rock music played

backwards when being told what to listen to



Our preexisting schemas (i.e. for monsters and tree trunks) influence how

we interpret ambiguous sensations w/ top-down processing

o Context Effects

A given stimulus can also trigger different perceptions due to context

• People struggle determining the gender of a baby, but when told

the gender, begin to perceive gender stereotypesV. Is There Extrasensory Perception?

- Extrasensory Perception (ESP): The controversial claim that perception can occur apart

from sensory input. Said to include telepathy, clairvoyance, and precognition

- Half or a little more of British and American adults and Japanese university students

say they believe in ESP, a quarter are unsure

- Parapsychology: The study of paranormal phenomena, including ESP and psychokinesis

o Have been amazed by psychic phenomena

- Claims of ESP

o Telepathy: mind-to-mind communication—one person sending thoughts to

another or perceiving another’s thoughtso Clairvoyance: Perceiving remote events

o Precognition: Perceiving future events

o Psychokinesis: “Mind over matter” (i.e. levitating a table)

o Premonitions or Pretensions?

Between 1978 and 1985, the New Year’s predictions of the National

Enquirer’s favorite psychics yielded 2 accurate predictions out of 486

When asked to submit dreams believed to hint at the whereabouts of

Charles Lindbergh’s baby, 4 out of 1300 predicted with completeaccuracy

Given the billions of events in the world each day, strange things are bound to happen

o Putting ESP to Experimental Test

After thousands of experiments, a reproducible ESP phenomenon hasnever been discovered, nor has anyone produced any individual who can

demonstrate psychic ability

Ganzfeld procedure: Subject placed in a reclining chair, listening tohissing noise in headphones and having ping pong balls strapped over

the eyes through which red light is shined (receiver). Sender had to focus

on picture, or something else, for 30 min

• 25 percent accuracy in original experiment, but disproven by a

successive experiment People believe in ESP through misperceptions, misinterpretations, and

selective recall, as well as an itch to experience the magical

CH6: Perception

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