Cognitive Psychology, Sixth Edition, Robert J. Sternberg Chapter 3

Cognitive Psychology, Fifth Edition, Robert J. SternbergChapter 3

Chapter 3: Visual Perception

Ted talk: beau lotto: optical illusions 2009

Cognitive Psychology, Sixth Edition, Robert J. SternbergChapter 3

Some Questions of Interest• What is sensation vs. perception?• What are two fundamental approaches

to explaining perception? • What happens when people with normal

visual sensations cannot perceive visual stimuli?


• Light waves• Sound waves

• Chemical molecules

• Chemical molecules

• Pressure/vibration

• Photon absorption• Conduction to basilar

membrane• Absorption in

olfactory epithelium• Contact with taste

buds• Stimulation of dermis

receptor cells

Distal vs. proximal stimuli



Our Visual System

Electromagnetic light energy is converted into neural electrochemical impulses


Our Visual System

Three main layers of retina– Ganglion cells– Amacrine cells, horizontal

cells, bipolar cells– Photoreceptors

• Rods and cones



Visual Pathways in the Brain“what”

• Temporal lobe lesions in monkeys

– Can indicate where but not what

“where” – Parietal lobe

lesions in monkeys– Can indicate

what but not where


Sensation does not equal perception!


Perceptual Basics• Sensory adaptation

– Occurs when sensory receptors change their sensitivity to the stimulus

• Our senses respond to change– Ganzfeld effect


Perceptual Constancy• Object remains the same even

though our sensation of the object changes– Size constancyvs. shape

constancy


Depth Perception– Monocular vs. binocular depth cues


• Texture gradients– Grain of item

• Relative size– Bigger is closer

• Interposition• Closer are in front of other objects• Linear perspective

– Parallel lines converge in distance

• Aerial perspective– Images seem blurry farther away

• Motion parallax– Objects get smaller at decreasing speed in distance

Monocular Depth Cues



Binocular Depth Cues• Binocular convergence• Binocular disparity


Perceptual Illusions• Sometimes we cannot

perceive what does exist

• Sometimes we perceive things that do not exist

• Sometimes we perceive what cannot be there


Perceptual Illusions

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


Visual illusions: brain function


Theories of Perception• Bottom-up vs top down theories


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– No complex thought processes

• EX: Use texture gradients as cues for depth and distance

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


Template Theoriescompare to templates in memory until a match is found

– Problem of imperfect matches


Feature-Matching Theories• Recognize objects by features

– Detect elements and assemble them into more complex forms

– Brain cells respond to specific features• lines and angles


Pandemonium Model

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


• Hubel & Wiesel (1979) – Simple cells – bars/edges– Complex cells –

bars/edgesdetect bars of particular orientation

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

Physiological Evidence for Features






CogLab: Visual Search

• Features vs. objects• The role of attention (next chapter)


Top-Down Processing (Constructive Approach)

• Perception is not automatic from raw stimuli– making inferences– guessing from experience


“Finished files are the result of years of scientific study combined with the experience of many years.”


•Context effectsContext 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 timeTarget alone = 1884 Composite = 749Target spotted faster in a context!

Target Composite


Gestalt’s View of Perception“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)• People have more difficulty recognizing

parts of faces than parts of houses


Fusiform Gyrus in Temporal Lobe

• pattern recognition– facial recognition– 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


Deficits in Perception• Disruption of the “what” pathway

– Agnosia: Inability to recognize and identify objects or people

• Disruption of the “what” pathway– Simultagnosic

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

object

• Prosopagnosia• Inability to recognize faces, including one's own


Visual Pathways in the Brain“what”

• Temporal lobe lesions in monkeys

– Can indicate where but not what

“where” – Parietal lobe

lesions in monkeys– Can indicate

what but not where


Deficits in Perception• Disruption of the “how” pathway

– Optic ataxia• Cannot use vision to guide movement• Unable to reach for items


Synesthesia Michael: “Flavors have shape,” he started, frowning into the depths of the roasting pan. “I wanted the taste of this chicken to be a pointed shape, but it came out all round. … When I taste something with an intense flavor,” Michael continued, “the feeling sweeps down my arm into my fingertips. I feel it—its weight, its texture, whether it’s warm or cold, everything. I feel it like I’m actually grasping something.” (p. 4)


Synesthesia Victoria:In response to a pager going off, said: “Oh, those blinding red jaggers! Turn that thing off,” she snapped. … “Your beeper made me see three red lightning bolts, brilliant red going up to the left.” She kept rubbing her head. “It’s usually not that strong, but it’s given me a splitting pain,” she continued. (pp. 47-48). “What makes you see things?” I asked. “Give us some details.” “Sharp, shrill sounds always do it,” she said, “like your beeper, or ambulance sirens, crashes, screeching tires.” … “Sudden sounds like that. Sometimes music will do it, if it’s loud enough and high enough in pitch,” she continued. … “I once heard a Chihuahua who drove me crazy with the sound of white spikes. But that can’t be the correct explanation, because words and names sometimes have color too.” (p. 48)


Perceptual Illusions and “construction”

• Phantom limb• synesthsia

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Cognitive Psychology, Sixth Edition, Robert J. Sternberg Chapter 3