chapter 6

CHAPTER 6

PERCEPTION

Selective Attention

Selective Attention: the focusing of conscious awareness on a particular stimulus

Selective Attention

Cocktail-Party Effect: the ability to attend to one of several speech streams while ignoring others (just as one is able to attend to one conversation among others at a cocktail party). In cases such as cocktail parties, the mention of one’s name is processed even if it occurs in an unattended speech stream.

Selective Attention

Inattentional blindness: failing to see visible objects when our attention is directed elsewhere Change blindness http://

www.youtube.com/watch?v=vBPG_OBgTWg Change deafness Choice blindness

http://www.youtube.com/watch?v=2pK0BQ9CUHk&feature=fvst

Perceptual Illusions

Visual CaptureThe tendency for vision to

dominate all other senses. Example?

Perceptual Organization Gestalt:

In German “Gestalt” means whole or form. The Gestalt psychologists studied perception and emphasized the fact that we can not study perception by examining its individual parts because quite often the whole is different (or more) than the sum of its parts.

Form Perception Figure-Ground

Relating to the principle that perceptions have two parts; a figure that stand out in good contour (the main elements of a scene), and an indistinct homogeneous background

Look at the plus sign in the middle, the pink/purple dots will disappear and be replaced by a green ring.

The circles are not moving. If you look at one it remains stationary while the other circles are moving.

Stare at the four black dots in the center of the image for 30 - 60 seconds. Then quickly close your eyes and look at something bright (like a lamp or a window

with sunlight coming through it). You should see a white circle with an image inside it.

An Old Woman or a Young Lady?

Proximity: The closer objects are to one another, the more likely they are to be perceived as belonging together

We perceive the picture figures below as one group of 2 circles, one single circle and another group of 2 circles.

Can you come up with examples of proximity as it relates to real life?

Gestalt Rules of Grouping

Gestalt Rules of Grouping Similarity: Similar elements are perceived

to be part of a group. For instance, all the players wearing blue shirts are from

the University of Michigan, all those wearing red are represent the University of Wisconsin

X O X OX O X OX O X OX O X O

We see two columns of Xs and two columns of Os not four rows of XOXO


Continuity: Sensations that appear to create a continuous form are perceived as belonging together

Once an object appears to move in a particular direction, your brain assumes that the movement continues unchanged. On some smaller highways, for example, you can easily miss your turn unless you really pay attention to the signs. We tend to assume that the highway continues in the direction we’ve been moving


ConnectednessWe perceive spots, lines, or areas as

a single unit when uniform and linked


Closure The tendency to fill in missing contours to

form a complete object

We perceive these objects as a circle and a square.

http://www.exploratorium.edu/brain_explorer/jumping.html


Common Fate: Sets of objects that move in the same direction at the same speed are perceived together

Examples: A flock of birds flying in a V formation, though separated in space, will be perceived as a group

Depth Perception

Depth Perception: The perception of distance, allowing us to experience the world in three dimensions. Monocular Depth cues Binocular Depth cues

Depth Perception

Visual CliffGibson and Walk

discovered that

6 month old infants

would not crawl to

their mothers if the were

on the “deep” side

Depth Perception

Binocular Cues: Depth cues requiring the use of two eye

Depth Perception

Retinal Disparity: A depth cue based on the difference between the retinal images received by each eye

Closer objects have

more retinal disparity

than objects farther

Depth Perception

As retinal disparity increases, perceived distance _________________.

As retinal disparity decreases, perceived distance _________________.

Depth Perception

Convergence: A depth cue resulting from rotation of the eyes so that the image of an object can be projected on each retina. The rotating of the eyes causes feelings of tension in the eye muscle. This tension is stronger when objects are closer

Depth PerceptionMonocular Depth cues: Depth

cues requiring the use of only one eyeLinear PerspectiveRelative SizeReduced ClarityInterposition/OverlappingTexture GradientRelative Height

Depth Perception

Relative Size: If two objects are assumed to be the same size, the object producing a larger image on the retina is perceived as closer than the one producing a smaller images

Depth Perception

Interposition/Overlapping: Closer objects block the view of objects farther away

Depth Perception

Reduced Clarity: Faraway objects seem less clear and less detailed

Depth Perception

Texture Gradient: A graduated change in the texture, or “grain” of the visual field. Texture appears finer as distance increases and coarser as the distance decreases.

Depth Perception

Relative height: More distant objects are usually higher in the visual field than those nearby

Depth Perception

Linear Perspective: The closer together two converging lines are, the greater the perceived distance

Depth Perception

Light and Shadow

(Relative Brightness)

A depth cue whereby dimmer objects appear to be farther away than bright objects

Depth Perception

Relative Motion (Motion Parallax)

When we are in motion, nearby objects will appear to move by rapidly while objects that are farther away will appear to move more slowly

Motion Perception

Our basic assumption is that shrinking objects are retreating, not shrinking and that enlarging objects are approaching

Stroboscopic Motion: the illusion of movement produced by showing the rapid progression of images or objects that are not moving at all

Phi Phenomenon: An illusion of apparent movement when two lights flash on and off in quick succession. The light appears to move from one location to the other

http://www.youtube.com/watch?v=gAvTTlXyzmE&feature=related

Perception

Perceptual Constancy: The ability to maintain a perception of the properties of an object (e.g. size, shape, color) regardless of changes in the actual stimulus conditions, such as the level of illumination, or image size on the retina

Perceptual Interpretation

Our perception is due to an interaction between nature and nurture

Critical PeriodThe critical period for normal sensory

and perceptual development is in infancy

Perceptual Adaptation

Humans are able to adapt perceptually. When people wear displacement goggles, they manage to adapt their movements and, with practice, to move about with ease. (Although kittens and monkey can also adapt, chicks cannot)

Perception

Perceptual SetA readiness or predisposition to perceive a stimulus in a certain way. Perceptual sets can save us time that is usually consumed by additional detail processing of stimulus features, but they can also lead to perceptual errors.

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

Rat-Man Illusion

What do these letters spell?

FolkCroakSoakYolk

Perception

Schemas: Mental representation of what we know, and

have come to expect about the world

Perception

Context EffectsA given stimulus may trigger radically

different perceptions because of the immediate context. For example, we discern whether a speaker said “morning” or “mourning” or “dye” or “die” from the surrounding words.

Perception and the Human Factor

Human Factors Psychologists: Explore how people and machines interact and how physical environments can be adapted to human behaviors. They help to

design appliances, machines,

and work settings that fit our

natural perceptions.

Is There Extrasensory Perception?

Extrasensory Perception (ESP): alleged awareness of external events by other means than the known sensory channels.

Parapsychology: the systematic study of alleged psychological phenomena involving the transfer of information or energy that cannot be explained in terms of presently known scientific data or laws


Three most testable varieties of ESP Telepathy: mind reading, thought

transference Clairvoyance: the alleged ability to “see”

beyond the normal range of sight, such as distant or hidden objects or events in the past or future

Precognition: the purported ability to see or experience future events


Psychokinesis: the alleged ability to control external events and move or change the shape of objects through the power of thought. An example is bending a piece of metal by exerting “mind over matter”

Anyone who believes in

psychokinesis, raise my hand


Premonitions or Pretensions? Research psychologists remain skeptical

because the acts of so-called psychics have typically turned out to be nothing more than the illusions of stage magicians, because checks of psychic visions have been no more accurate than guesses made by others, and because sheer chance guarantees that some stunning coincidences are sure to occur


Putting ESP to Experimental TestAn important reason for psychologists

skepticism, is the absence of reproducible ESP results. In addition, to believe in ESP, one must believe that the brain is capable of perceiving without sensory input.

chapter 6

Documents

german gestalt

gestalt psychologists

single circle

continuous form

particular direction

visible objects

closer objects

cocktail party