Sensation and
Perception
Chapter 5
1
Sensation and Perception
Definitions
Sensing the World:
 Thresholds
 Sensory Adaptation
Vision
 The Stimulus Input:
Light Energy
Perceptual Organization
 Form Perception
 Depth Perception
 Perceptual
Constancy
Perceptual Interpretation
 The Eye
 Sensory Deprivation
and Restored Vision
 Visual Information
Processing
 Color Vision
 Perceptual
Adaptation
 Perceptual Set
2
FINISHED FLIES ARE THE
RESULT OF YEARS OF
SCIENTIFIC STUDY
COMBINED WITH THE
EXPERIENCES OF YEARS
3
Sensation & Perception
How do we construct our representations of the
external world?
To represent the world, we must detect physical
energy (a stimulus) from the environment and
convert it into neural signals. This is a process
called sensation.
When we select, organize, and interpret our
sensations, the process is called perception.
4
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.”
5
Top-Down Processing
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
THE CHT
6
Making Sense of Complexity
Our sensory and perceptual processes work
together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle
7
Psychophysics
A study of the relationship between physical
characteristics of stimuli and our psychological
experience with them.
Physical World
Psychological
World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet
8
Exploring the Senses
What stimuli cross our threshold for
conscious awareness?
9
Thresholds
Proportion of “Yes” Responses
1.00
0.50
0.00
Absolute Threshold: Minimum stimulation needed
to detect a particular stimulus 50% of the time.
0
5
10
15
20
Stimulus Intensity (lumens)
25
10
Sensing the World Around Us
Absolute threshold
The smallest intensity of
a stimulus that must be
present for it to be
detected
11
Subliminal Threshold
Subliminal Threshold:
When stimuli are below
one’s absolute threshold for
conscious awareness.
Kurt Scholz/ Superstock
12
Puzzles of Perception
• Can we ever perceive what is happening
below our usual sensory threshold?
• Can we pick up signals from world or from
other people without using our usual
sensory channels at all?
13
6
Perceiving without Awareness
Priming
A method used to insure unconscious processes, in
which a person is exposed to information and is
later tested to see whether the information affects
behavior or performance on another task or in
another situation
Findings suggest simple primes influence perception, memory, thinking,
and decision-making.
14
6
Perception vs. persuasion
Although subliminal priming can influence
judgments and preferences, research doesn’t
support its success in major levels of
persuasion.
15
6
Extrasensory perception
ESP
The ability to perceive something without ordinary sensory information
Has not been scientifically demonstrated
16
6
Difference threshold
The smallest difference in stimulation that
can be reliably detected by an observer when
two stimuli are compared
Also called the Just Noticeable Difference
(JND)
Also known as Weber’s Law
17
Sensory Adaptation
Diminished sensitivity as a consequence of
constant stimulation.
Put a band aid on your arm and after awhile
you don’t sense it.
18
Vision
19
Transduction
In sensation, the transformation of stimulus energy
(sights, sounds, smells) into neural impulses.
20
Both Photos: Thomas Eisner
The Stimulus Input: Light Energy
Visible
Spectrum
21
Physical Characteristics of Light
1. Wavelength (hue/color)
2. Intensity (brightness)
22
Wavelength (Hue)
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Different wavelengths of light result
in different colors.
23
Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
24
The Eye
25
Parts of the eye
1. Cornea: Transparent tissue where light enters
the eye.
2. Iris: Muscle that expands and contracts to
change the size of the opening (pupil) for light.
3. Lens: Focuses the light rays on the retina.
4. Retina: Contains sensory receptors that process
visual information and sends it to the brain.
26
The Lens
Lens: Transparent
structure behind the
pupil that changes shape
to focus images on the
retina.
Accommodation: The
process by which the
eye’s lens changes shape
to help focus near or far
objects on the retina.
27
Retina
Retina: The lightsensitive inner
surface of the eye,
containing receptor
rods and cones in
addition to layers of
other neurons
(bipolar, ganglion
cells) that process
visual information.
28
Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the
brain. Blind Spot: Point where the optic nerve leaves the
eye because there are no receptor cells located there.
Fovea: Central point in the retina around which the eye’s
cones cluster.
http://www.bergen.org
29
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
30
Visual Information Processing
Optic nerves connect to the thalamus in the
middle of the brain, and the thalamus connects to
the visual cortex.
31
Feature Detection
Ross Kinnaird/ Allsport/ Getty Images
Nerve cells in the visual cortex respond to
specific features, such as edges, angles, and
movement.
32
Shape Detection
Ishai, Ungerleider, Martin and Haxby/ NIMH
Specific combinations of temporal lobe activity
occur as people look at shoes, faces, chairs and
houses.
33
6
Trichromatic theory
Young (1802) and von
Helmholtz (1852) both
proposed that the eye
detects 3 primary
colors
Red, blue, and green
All other colors
derived by
combination
34
Color Blindness
Genetic disorder in which people are blind to
green or red colors. This supports the
Trichromatic theory.
Ishihara Test
35
6
Afterimages
36
37