INTRODUCTION TO PSYCHOLOGY

Chapter 5

Perception

At the end of this Chapter you should be able to:

• Understand what Distance Perception is

• Understand what Motion Perception is

• Understand what Form Perception is

• Learn about Attention

• Learn about Visual Illusions

Visual Perception

• The retinal image is only two-dimensional; height and width...

• From the two-dimensional images that fall on our retinas we somehow are able to see three-dimensional objects.

Visual Perception

• Seeing objects in three dimensions, or depth perception, allows us to estimate distances between those objects and us.

Visual Perception

• Psychologists are particularly interested in the cues which enable people to perceive depth and distance. These cues may be monocular, effective when using one eye as well as two, or binocular, requiring the usage of both eyes.

Depth & Distance Perception

• Depth Perception: Ability to see three-dimensional space and to accurately judge distances

• Depth Cues: Features that supply information about distance and space.

Depth & Distance Cues

– Binocular cues

• We compare the retinal image in one eye to the retinal image in the other; they differ: each eye is a slightly different distance from an object in the world

Depth & Distance Cues

– Monocular cues

• Interposition

• Linear perspective

• Texture Gradients

• Relative Size

• Light and Shadow

• Motion Parallax

Binocular disparityBinocular disparity

The disparity between the The disparity between the views serves as a powerful cue views serves as a powerful cue for depthfor depth

Monocular Cues: Interposition

Interposition: When one object partly blocks your view of another, you perceive the partially blocked object as farther away

Monocular Cues: Interposition

InterpositionInterposition: : The fact that mailbox blocks the view The fact that mailbox blocks the view is a powerful cue that the mailbox must be closer is a powerful cue that the mailbox must be closer to the observer than the sport car isto the observer than the sport car is

Monocular Cues: Interposition

Madonna of the Magnificat by Sandro Botticelli.

Monocular Cues: Linear Perspective

Linear PerspectiveLinear Perspective:: Parallel lines that are known Parallel lines that are known to be the same distance apart appear to grow to be the same distance apart appear to grow closer together, or converge, as they recede into closer together, or converge, as they recede into the distancethe distance

Monocular Cues: Linear Perspective

Monocular Cues: Texture Gradient

Texture GradientsTexture Gradients: : The texture of objects tend to become smoother as The texture of objects tend to become smoother as the object gets farther away, suggesting that more detailed textured the object gets farther away, suggesting that more detailed textured objects are closer. objects are closer. 

Monocular Cues: Relative Size

••Relative sizeRelative size: : Larger objects are perceived as being closer Larger objects are perceived as being closer to the viewer, and smaller objects as being farther awayto the viewer, and smaller objects as being farther away

Monocular Cues: Relative Size

Monocular Cues: Light and Shadow

Monocular cues: Monocular cues: light and shadowlight and shadow: (A) Eight circular objects. To : (A) Eight circular objects. To most viewers, the one in the middle looks concave, indented, whereas most viewers, the one in the middle looks concave, indented, whereas other seven look as if they are bulging out. (B) The same figure rotated other seven look as if they are bulging out. (B) The same figure rotated 180 degrees. Now, the middle object looks convex, while others seem 180 degrees. Now, the middle object looks convex, while others seem concave. The reason is the location of the shadow. If the shadow is at concave. The reason is the location of the shadow. If the shadow is at the bottom, the object looks convex, if the shadow is at the top, the the the bottom, the object looks convex, if the shadow is at the top, the the object looks concave. object looks concave.

Monocular Cues: Light and Shadow

Monocular Cues: Motion Parallax

• When you ride in a moving vehicle and look at the side window, the objects you see appear outside move in opposite direction

• Objects seem to be moving in different speeds-the ones that are closer to you seem to move faster, whereas objects far behind seem to move slower

Monocular Cues: Motion Parallax

Perceptual Constancy

The tendency to perceive objects as maintaining stable properties (e.g., size, shape, brightness, and color) despite differences in distance, viewing angle, and lighting

Size Constancy

Size constancy refers to our ability to see objects as maintaining the same size even when our distance from them makes things appear larger or smaller. 

Shape constancy   

Shape ConstancyShape Constancy:: Perceiving objects as having a stable Perceiving objects as having a stable or unchanging shape regardless of changes in the retinal or unchanging shape regardless of changes in the retinal image resulting from differences in viewing angleimage resulting from differences in viewing angle

VIDEO of Julian Beever, an English artist, who paints sidewalks in an

amazing 3-D way....

Motion Perception

• Perception of an event -motion- rather than an object

• Motion tells us what the object is doing.

Apparent motion

• When intervals between images occur at correct timing (not too far apart in time) we perceive motion

• This principle used to create ‘motion’ from stills

Apparent motion

• In movies, when still pictures are put together, it produces the sensation of movement for the viewer (audience). Even though there is no ACTUAL movement.

• We do not only detect motion but we also interpret it.

Apparent Movement

Apparent motion

• Motion

What about the variability in objects that we see?

• The same animal but the features look different. So how can we classify all of them as a giraffe?

What about the variability in objects that we see?

• We recognize giraffes as being giraffes whether we see them from the side, or the front, or close up, or from far away.

• Do we actually pay attention to every detail (feature)?

• We only interpret crucial information. We don’t have time in the real-world to pay attention to every little detail. Otherwise we cannot survive!

Form Perception

• Detecting object features (parts)

• The importance of organization

• Perceptual parsing

• Separating the figure from the ground

Organization’s role in perception

• Features: some we ignore, some we attend to

• How do we decide whether to ignore or attend?

• We interpret some features as being part of the object, other features as irrelevant

• How do we group together features that belong with each other?

A hidden figureA hidden figure

Missing featuresMissing features

Gestalt Psychology

• The German word "Gestalt" roughly means to "whole" or "form"

• “The whole is greater than the sum of its parts.” 

• In order to interpret what we receive through our senses, we attempt to organize this information into certain groups. – Sense of shape: derived from the whole,

not the sum of its parts

Gestalt principles organization

• Perceptual parsing:– Segregating the “scene” into its constituent

objects– The first step to organizing

• Gestalt principles of organization:• Issues of figure/ground• Similarity• Proximity• Good continuation

–“subjective contours”

Perseptual ParsingPerseptual Parsing

Grouping by similarityGrouping by similarity

Grouping by proximityGrouping by proximity

Good ContinuationGood Continuation

Subjective contoursSubjective contours

Gestalt psychology

– Important: Is the object figure or ground?• Our interpretation of figure / ground will influence how we perceive an object

Reversible figure-ground patternReversible figure-ground pattern

http://www.michaelbach.de/ot/cog_dalmatian/index.html

The classical approach to perception

• Emphasis on the active, constructive role of the perceiver, who routinely:– Resolves ambiguous figures– Determines identity of objects based on

contextual clues and previous knowledge– Determines identity of objects based on

contextual clues

Ambiguous Necker CubeAmbiguous Necker Cube

Contextual clues (and previous knowledge)Contextual clues (and previous knowledge)

Illusions: How could we make such mistakes?

• Cues sometimes cause an over-estimate or under-estimate;

• Slight over/under interpretations can cause us to misinterpret the information we receive

• Usually: – perceptions are accurate– are based on relevant experience– reflect the world we live in

The Ponzo IllusionThe Ponzo Illusion

Brightness IllusionBrightness Illusion

Perceptual selection: Attention

• What starts the synchrony? One possible mechanisms: ATTENTION

• Selective control of orientation

– Selective looking

• Difficult when target represents multiple, rather than a single, feature

VIDEO on Attention 1(when you do not expect to see

any changes)

VIDEO on Attention 2 (when you expect to see

changes)

Some final thoughts: Seeing, knowing, and the perceiver’s

active role

• Perception is not knowledge

• Knowledge and perception are mutually influenced, but are not the same thing: the perceiver and the knower are distinct in many instances

In this experiment, subjects were asked to , subjects were asked to keep the keep the track of the ball players in white shirtstrack of the ball players in white shirts. Intent on their . Intent on their task, the subjects were not paying any attention to task, the subjects were not paying any attention to the black shirted players, even though they are the black shirted players, even though they are looking directly at them. looking directly at them.

AND THEY ALSO FAILED TO SEE .....AND THEY ALSO FAILED TO SEE .....

VIDEO about the blind Turkish artist Eşref Armağan

Web Links for Optical Illusions

• Mueller-Lyer Illusion

• Brightness Illusion

• Checker-Shadow Illusion

Attention Demos

The Stroop Effect

As fast as you can, read the names of the colors

As fast as you can, (don’t read the word) but read the name of the color of the word.

As fast as you can, (don’t read the word) but read the name of the color of the word.

As fast as you can, (don’t read the word) but read the name of the color of the word.