Cognitive Psychology, Fifth Edition, Robert J. Sternberg Chapter 3 Chapter 3: Visual Perception.

Cognitive Psychology, Fifth Edition, Robert J. SternbergChapter 3

Chapter 3: Visual Perception

Cognitive Psychology, Sixth Edition, Robert J. SternbergChapter 3

Some Questions of Interest

• How can we perceive an object like a chair as having a stable form, given that the image of the chair on our retina changes as we look at it from different directions?


Some Questions of Interest

• What are two fundamental approaches to explaining perception?

• What happens when people with normal visual sensations cannot perceive visual stimuli?


Perception Is…

• The process of recognizing, organizing, and interpreting information

• How do you recognize these items?


Basic Concepts

• Distal object– Grandma’s face

• Informational medium– Reflected light from Grandma’s face

• Proximal stimulation– Photon absorption in the rod and cone

cells of the retina

• Perceptual object – Grandma’s face


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–Ganzfeld effect


Perceptual Illusions

• Sometimes we cannot perceive what does exist

• Sometimes we perceive things that do not exist



• Sometimes we perceive what cannot be there



• Some other illusions to explore:–http://www.michaelbach.de/ot/#history

http://www.michaelbach.de/ot/#history


Our Visual System

• Light travels through the eye and focuses on the retina –Electromagnetic light

energy is converted into neural electrochemical impulses


Our Visual System

• Three main layers of neural tissue in retina–Ganglion cells–Amacrine cells,

horizontal cells, bipolar cells

–Photoreceptors• Rods and cones


Visual Pathways in the Brain

• What/where hypothesis–One path for identifying

• Temporal lobe lesions in monkeys– Can indicate where but not what

–Another for spatially locating• Parietal lobe lesions in monkeys

– Can indicate what but not where


Visual Pathways: Alternative

• What/how hypothesis–Where something is located in space–How do we reach for it?


Theories of Perception• Bottom-up theories

–Parts are identified, put together, and then recognition occurs

• Top-down theories–People actively construct perceptions

using information based on expectations


Bottom-Up Processing Theories

• Direct perception• Template theories• Feature-matching theories• Recognition-by-components theory


Gibson’s Theory of Direct Perception

• The information in our sensory receptors is all we need to perceive anything–Do not need the aid of complex

thought processes to explain perception



• Use texture gradients as cues for depth and distance– Allows us to perceive directly the relative

proximity or distance of objects



• Mirror neurons start firing 30-100 ms after a visual stimulus


Template Theories

• Basics of template theories–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 Theories

• 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


Feature-Matching 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”


Pandemonium Model

• Four kinds of demons– Image demons– Feature demons– Cognitive demons– Decision demons


• Participants asked what they saw on the• Global level• Local level

• Results depended on whether letters are more widely spaced

• Participants were faster at identifying local features of the letters

Navon (1977)


• Hubel & Wiesel (1979) – 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

Physiological Evidence for Features


• Biederman (1987)–Describes how 3D

images are identified –Breaks objects down

into geons –Objects are identified

by geons, relationship between them

Recognition-by-Components (RBC) Theory


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

• BUT there are neurons sensitive to viewpoint-invariant properties


Top-Down Processing (Constructive Approach)

• 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


•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.

Evidence for Top-Down Processing


Configural-Superiority Effect

• Objects presented in context are easier to recognize than objects presented alone

• Task: Spot the different stimuli, press button


Configural-Superiority Effect

Measure reaction time

Target alone = 1884 Composite = 749

Target spotted faster in a context!

Target Composite


Which Approach Is Right?

• Top-down or bottom-up–Perhaps a bit of both


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


Landmark-Centered Orientation

• Information is coded by its relation to a well-known or prominent item

• Consider your college campus–What is a prominent item you use to

orient yourself on campus?


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



• 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 images

C

B

A

D


Pattern Recognition Systems

• Feature analysis system–Recognize parts of objects–Assemble parts into wholes

• Configurational system–Recognize larger configurations


• Tanaka & Farah (1993)–Participants studied

• Faces and names• Pictures of homes and home owner’s names

–At test, given only a piece of face (e.g., nose), whole face, whole home, or a piece of the home (e.g., window)• Asked to recall names

Evidence for Separate Systems


Tanaka & Farah (1993)

• Results• People have more difficulty recognizing

parts of faces than parts of houses


Fusiform Gyrus in Temporal Lobe

• Implicated in pattern recognition• Studies illustrate it is active in facial

recognition• However, also active if high

expertise in any item (birds, cars) recognition–Expert individuation hypothesis


• Prosopagnosia– Inability to recognize faces after brain

damage–Ability to recognize objects is intact

• Associative agnosia–Difficulty with recognizing objects–Can recognize faces

Evidence for Separate Systems


Perceptual Constancy

• Object remains the same even though our sensation of the object changes–Size constancyvs. shape

constancy


Depth Perception

• The ability to see the world in three dimensions and detect distance– Vision only has a two-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


Monocular Depth Cues

• Linear perspective–Parallel lines converge in distance

• Aerial perspective– Images seem blurry farther away

• Motion parallax–Objects get smaller at decreasing

speed in distance


Binocular Depth Cues

• Binocular convergence–Eyes turn inward as object moves

toward 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 3D image


Agnosias, Ataxias, & Cognition

• Demonstrate the modularity of cognition

• Help us to understand what brain locations are associated with different types of higher-level processing

• Provide us with a model of how normal processing must work


Deficits in Perception

• Disruption of the “what” pathway–Agnosia

• Inability to recognize and identify objects or people, despite having knowledge of the characteristics of the objects or people

•Shows the specialization of our perceptual systems



• Disruption of the “what” pathway–Simultagnosic

•Normal visual fields, yet act blind•Perceives only one stimulus at a time—

single word or object


• Disruption of the “what” pathway–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




• Disruption of the “how” pathway–Optic ataxia

• Cannot use vision to guide movement• Unable to reach for items

Cognitive Psychology, Fifth Edition, Robert J. Sternberg Chapter 3 Chapter 3: Visual Perception.

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