perception

Cognitive Psychology, Fourth Edition, Robert J. SternbergChapter 4

Chapter 4: Perception

Perception Is…

• The process of recognizing, organizing and interpreting information

• How do you recognize these items?

Perceptual Basics

• Sensory Adaptation– Occurs when sensory receptors change

their sensitivity to the stimulus

– Constant stimulation leads to lower sensitivity

• Our senses respond to change

Perceptual Basics

• Perceptual Constancy– Object remains the

same even though our sensation of the object changes

• Example: – Shape constancy

Depth Perception• The ability to see the world in 3 dimensions

and detect distance– Vision only has a 2-dimensional view

– We must interpret the information given to perceive depth

– We take flat images and create a three dimensional view

– Optical illusions demonstrate that this interpretation does not always have to be correct

• Texture Gradients– Grain of item

• Relative Size– Bigger is closer

• Interposition– Closer are in

front of other objects

Monocular Depth Cues

• Linear Perspective– Parallel lines

converge in distance

• Aerial Perspective– Images seem blurry,

the farther away

• Motion Parallax– Objects get smaller

at decreasing speed in distance

Binocular Depth Cues

• Binocular Convergence– Eyes turn inward as object moves

towards you, brain uses this information to judge distance

• Binocular Disparity– Each eye views a slightly different angle

of an object; Brain uses this to create a 3-d image

Object Perception

• Viewer-centered representation – Object is stored in the perspective seen– Store multiple views of object as seen under

various conditions – Viewpoint dependent process

• Object-centered representation – Object is stored in a way that best represents the

object – Viewpoint invariant process

Object Perception

• Evidence supports both

• How to reconcile?– Maybe both contribute to object

recognition– Two ends of a continuum that contribute

to object recognition– Burgund & Tarr researched this issue

Gestalt’s View of Perception

• Basic Tenet– “The whole is more than a sum of its parts.”

• Law of Prägnanz– Individuals organize their experience in as

simple, concise, symmetrical and complete manner as possible

Gestalt’s Principles of Visual Perception

• Figure-Ground– Organize perceptions by

distinguishing between a figure and a background

• Proximity– Elements tend to be grouped together

according to their nearness

• Similarity– Items similar in some respect tend to

be grouped together

Gestalt’s Principles of Visual Perception• Continuity

– Based on smooth continuity which is preferred to abrupt changes of direction

• Closure– Items are grouped together if

they tend to complete a figure

• Symmetry– Prefer to perceive objects as

mirror imagesKanizsa's Figure

Theories of Perception

• Direct Perception theories– Perception comes from the stimuli in the

environment– Bottom up processing – Parts are identified, put together, and then

recognition occurs

• Constructive Perception theories– People actively construct perceptions using

information based on expectations– Top down processing

Gibson’s Direct Perception (Ecological model)

• All the information needed to form a perception is available in the environment

• Perception is immediate and spontaneous

• No top down processing is necessary

• Perception and action cannot be separated

• Perception guides action and action generates more new perceptual information

Bottom Up Processing Theories

• Template theories

• Prototype theories

• Feature theories

• Structural description theories

Template Theory

• Basics of template theory– Multiple templates are held in memory

– To recognize the incoming stimuli, you compare to templates in memory until a match is found

See stimuli

Search memory for a match

Template Theory

• Weakness of theory– Problem of imperfect matches

– Cannot account for the flexibility of pattern recognition system

See stimuli No perfect match in memory

Search for match in memory

Prototype Theories• Modification of template matching

(flexible templates)

• Takes various instances of an object and abstracts out the common characteristics

• No match is perfect; a criterion for matching is needed

Prototype Evidence

• Franks & Bransford (1971)– Presented objects based on prototypes

– Prototype not shown

– Yet participants are confident they had seen prototype

– Suggests existence of prototypes

Prototype Evidence

• Solso & McCarthy (1981)– Participants were shown a

series of faces

– Later, a recognition test was given with some old faces, a prototype face, and some new faces that differed in degree from prototype

Solso & McCarthy (1981) Results

• The red arrow notes that participants were more confident they had seen the prototype than actual items they had seen

Research on Prototypes

• Researchers have found that prototypical faces are found to be more attractive to participants

• Halberstadt & Rhodes (2000)– Examined the impact of prototypes of dogs,

wristwatches, and birds on attractiveness of the stimuli

– Results indicate a strong relationship between averageness and attractiveness of the dogs, birds, and wristwatches

Feature Theories

• Recognize objects on the basis of a small number of characteristics (features)– Detect specific elements and assemble them

into more complex forms

– Brain cells that respond to specific features, such as lines and angles are referred to as “feature detectors”

Feature Evidence

• Hubel & Wiesel (1979) using single cell technique– Simple cells detect bars or edges of particular

orientation in particular location – Complex cells detect bars or edges of

particular orientation, exact location abstracted – Hypercomplex cells detect particular colors

(simple and complex cells), bars, or edges of particular length or moving in a particular direction

Structural-Description Theories

• Biederman (1987)– Describes how 3D

images are identified

– Breaks objects down into geons

– Objects are identified by geons and relationship between them

Evidence of Geons•Beiderman (1987) Can you identify these objects?

These objects have been rendered unidentifiable because their geons are nonrecoverable

Evidence of Geons• Beiderman (1987)

• Can you identify these objects?

These objects have had the same amount of the object taken out but because the geons can still be recreated, one can recover the objects

Evidence for Geons

• Beiderman (1987) demonstrated the importance of the use of geons to recognize objects

Original Recoverable Nonrecoverable

Evidence for Geons

• Biederman & Cooper (1991)– Used visual priming to demonstrate the

existence of geons in a picture naming task– Subjects were shown a series of fragmented

pictures and were asked to identify the objects

Biederman & Cooper (1991)

After naming novel objects, the second phase begins …

Name these fragmented objects

Biederman & Cooper (1991)

1st fragment Complementary fragment Different exemplar

Several different kinds of stimuli were used: identical repeats, complementary, novel, and different exemplars. Reaction time to name object was noted.

Biederman & Cooper (1991) ResultsReaction time for identical and complementary stimuli was faster demonstrating visual priming.

Visual priming could only occur if participants had created the whole geon when exposed to the first fragmented image.

Top-down Processing (Constructive Perspective)

• Perception is not automatic from raw stimuli

• Processing is needed to build perception

• Top down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another

Top-down Processing Evidence

•Context effects

Context helps us to be able to recognize letters in many different styles.

Context helps us to be able to recognize letters in many different styles.Context helps us to be able to recognize letters in many different styles.

Palmer (1975) Context Effect•Showed participants a related scene, an unrelated scene, or no context•Immediately after, asked participants to name a briefly seen object •Objects that were appropriate to the scene (or context)•were recognized more rapidly than objects that were unrelated to the scene

Marr’s Computational Theory

edgescontours

blobs depth&

orientation

depth&

orientationreal shapereal shape

2-D Primal sketch

2.5-D Sketch3-D model

representation

Deficits in Perception

• Agnosia– Inability to recognize and identify objects

or persons despite having knowledge of the characteristics of the objects or persons

– Shows the specialization of our perceptual systems

Perceptual Deficits• Prosopagnosia

– Inability to recognize faces, including one's own

– Cannot recognize person from face– Knows a face is a face – Can recognize individuals from voice – Can recognize objects– Can discriminate whether two faces are

same or different

Deficits in Perception• Simultagnosic

– Normal visual fields, yet act blind

– Perceives only one stimulus at a time—single word or object

perception

visual priming

feature theories

solso amp

dimensional

gestalts principles

centered representation

biederman

visual perception

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