• Outline» Chap. 3

◊ Visual Perception– Unconscious inferences– Preattentive organization – Retinal vs. cortical effects

– Gathering Visual information

– Visual Sensory Memory

Study Questions.Describe the unconscious inference theory of Helmholtz. How does the theory explain some visual illusions?Describe the gestaltist principles of groupingDefine visual sensory memory. How did Sperling empirically distinguish between a capacity and a duration hypothesis.

04/21/23

Perception and Pattern Recognition

• Visual Perception

Perception and Pattern Recognition

• Visual Perception

Perception

• Perception is in the brain» Melzak : “Pain is in the brain”

◊ Phantom limb pain

» Filling in the blind spot» Complimentary colour mixing» Visual illusions

◊ E.g., The moon illusion

◊ Other illusions

Perception

• The unconscious inference theory (helmholtz)» Analyze cues in sensory input

» Construct a perception with depth, size and motion.

» Send perception on to conscious mind.

• The Müller-Lyer illusion

Perception

• Problems with the unconscious inference explanation.

Perception

• The frame illusion

Perception

» Assimilation theory: We incorporate nearby elements into an object’s boundary when assessing size.

Online Demo

Perception

• Size illusions based on linear perspective

Chasing illusion

Example 1

A great size constancy illusion: The power of persective

Shadow and ball illusion

Coding of Contrast and Contour

• Three examples of exaggerated contrast

Coding of Contrast and Contour

• Receptive fields and on-off areas

-

-- - -

-

-

-----

-

+ + + +

• Contrast heightening

Hermann - Hering grid

• Receptive fields and the Hermann-Hering illusion

Gestalt Perception

• Sensation and bottom-up processing

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

-> Perception involves an interplay between bottom-up and top-down processes.

• Context and top-down processing.

• Pitting the gestalt against sensation

• Illusions deriving from top-down processing

Gestal principles of grouping

• Proximity.

Gestal principles of grouping

• Similarity.

Gestal principles of grouping

• Closure.

Gestal principles of grouping

• Good continuation.

Online Demo

Figure/ground

• We divide a visual scene into figure (the object to which we attend) and ground (background).

Example 1:

Example 2: Figure and Ground in MC Escher’s art.

Example 3:

Rubin Vase by Shigeo Fukuda

Perception and Pattern Recognition

• Visual auras and migraine headaches» Cortical or retinal?

◊ A retinal effect:

Perception and Pattern Recognition

• Visual auras and migraine headaches» Cortical or retinal?

◊ A retinal effect:

◊ A cortical effect:

Perception and Pattern Recognition

• Extracting visual information» Saccades - eye movements, which occur in a jerking,

start-stop fashion.

Perception and Pattern Recognition

• Visual sensory memory» Visible persistence» Selection from brief displays

H L B M

Q Y X S

E T W R

F Z N Q

W U C D

R Y E T

G X M W

E I V F

T U R Y

Perception and Pattern Recognition

• Visual sensory memory» Visible persistence» Selection from brief displays

» Original findings◊ Observers remember 4 or 5 items (span of apprehension)◊ Sperling’s question: Where is the limitation?

– Capacity hypothesis: The visual system only registers 4 or 5 items– Duration hypotheis: All the letters get registered but fade rapidly

◊ The partial report procedure– E.g., Standing’s experiment

George Sperling

Perception and Pattern Recognition

• Visual sensory memory» Sperling’s results

Cue Delay (Seconds)Full

Report

0 .15 .30 1.0

0

2

4

6

8

10

Est

imat

ed #

lette

rs a

vaila

ble

Perception and Pattern Recognition

• Visual sensory memory» Visual Masking» Averbach and Coriell (1961)

◊ Two types of cues: Bar markers and circles◊ Partial report of 1 item.

J V W RT P N H

Y Q M XS O K I

J V W RT P N H

Y Q M XS O K I

Perception and Pattern Recognition

• Visual sensory memory» Averbach and Coriell (1961)

Cue Delay (ms)

0 100 200 300

0

20

40

60

80

100

Per

cent

age

Cor

rect

-100 400 500

Bar probe

Circle probe

Perception and Pattern Recognition

• Visual sensory memory» Is selection from VSM precategorical?

◊ Merikle (1980)

◊ Demo

H 6 B M

8 Y X S

E 7 W 9

Perception and Pattern Recognition

• Visual sensory memory» Is selection from VSM precategorical?

◊ Merikle (1980)

◊ Demo

A

R

8

T

A

R

G

T

3 6

G5

8

3 6

5

Correlated physical dimension

Present Absent

Perception and Pattern Recognition

• Visual sensory memory» Is selection from VSM precategorical?

◊ Merikle (1980)

◊ Demo

Correlated Physical Dimension

Present Absent

Partial

Whole

6.4

4.4

5.5

4.2

Perception and Pattern Recognition

• Visual sensory memory» Literal representation

◊ Template matching

Perception and Pattern Recognition

• Visual sensory memory» Other issues

◊ Ecological validity