Sensation and Perception

Chapter 6

Sensation

3

The Eye

4

Photoreceptors

E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Perception

6

Test your Blind Spot

Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from

your eye. At some point the car on the right will disappear due to a blind spot.

7

Bottom-up Processing

Analysis of the stimulus begins with the sense receptors and works up to the level of

the brain and mind.

Letter “A” is really a black blotch broken down into features by the brain that we perceive as an

“A.”

8

Feature Detection

Nerve cells in the visual cortex respond to specific features, such as edges, angles,

and movement.

Ros

s K

inna

ird/

Alls

port

/ Get

ty I

mag

es

9

Visual Information Processing

parallel processing The brain divides a visual scene into subdivisions such as color,

depth, form, movement, etc.

10

Top-Down Processing

Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience

and expectations.

THE CHT

11

Thresholds

Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50%

of the time.

Pro

port

ion

of

“Yes”

Resp

on

ses

0.0

0

0

.50

1.0

0

0 5 10 15 20 25 Stimulus Intensity (lumens)

12

Subconscious Sense and Perception

Subliminal Threshold: PrimingLength of effects

Adaptation/Habituation

• Stare at the image, don’t move your eyes around

15

Perceptual Organization

Flipped image

17

Figure/GroundT

ime S

avings Suggestion, ©

2003 Roger S

heperd.

18

Grouping

19

Depth Perception

Visual Cliff

Inne

rvis

ions

20

Binocular Cues

Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when

pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in

the inset.

21

Monocular Cues

Relative Size: If two objects are similar in size, we perceive the one that casts a

smaller retinal image to be farther away.

22

Monocular Cues

Interposition: Objects that occlude (block) other objects tend to be perceived as closer.

Rene M

agritte, The Blank Signature, oil on canvas,

National G

allery of Art, W

ashington. Collection of

Mr. and M

rs. Paul Mellon. Photo by R

ichard Carafelli.

23

Monocular Cues

Relative motion:

24

Monocular Cues

Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the

greater their perceived distance.

© T

he New

Yorker C

ollection, 2002, Jack Ziegler

from cartoonbank.com

. All rights reserved.

25

Monocular Cues

Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to

be farther away.

From

“Perceiving S

hape From

Shading” by V

ilayaur S

. Ram

achandran. © 1988 by S

cientific Am

erican, Inc. A

ll rights reserved.

26

Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal

images change.

27

Color Constancy

Color Constancy

28

Lightness Constancy

The color and brightness of square A and B are the same.

Courte

sy E

dwar

d Ade

lson

29

Size-Distance Relationship

From Shepard, 1990

Alan C

hoisnet/ The Im

age Bank

30

Size-Distance RelationshipBoth girls in the room are of similar

height. However, we perceive them to be of different heights as they stand in the

two corners of the room.

Both photos from S. Schwartzenberg/ The Exploratorium

31

Ames Room

The Ames room is designed to demonstrate the size-distance illusion.

32

Perceptual Interpretation

How important is experience in shaping ourperceptual interpretation?

33

Facial Recognition

After blind adults regained sight, they

were able to recognize distinct features, but

were unable to recognize faces.

Normal observers also show difficulty in facial recognition when the

lower half of the pictures are changed.

Courtesy of R

ichard LeG

rand

34

Kittens raised without exposure to horizontal lines later had difficulty

perceiving horizontal bars.

Blakemore & Cooper (1970)

Sensory Deprivation

Top down emotional effects

• Music• Fatigue• Carrying heavy versus light objects• Previous performance

36

To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting

under a tree.

Cultural Context

Context instilled by culture also alters perception.

37

Taste

Sweet Sour Salty Bitter Umami(FreshChicken)

Gustation/Taste – a close-up view of the tongue

Why does some food taste “hot”?

• Hot chili peppers are sensed by pain fibers in the tongue, which are activated by capsaicin

• Was evolved in the peppers to prevent them from being eaten

40

Smell

What is your favorite scent?

42

Smell and Memories