This document discusses concepts related to sensation and perception from an introductory psychology perspective. It begins by defining sensation as the activation of sense organs by physical stimuli. It then describes the various sensory receptors and modalities humans possess. Thresholds such as absolute threshold and just noticeable difference are explained. The document also outlines the visual system in detail, including parts of the eye and visual pathways. Finally, it discusses perception as the interpretation and meaning-making of sensations, and various perceptual phenomena such as constancies and depth perception.

1. © The McGraw-Hill Companies, Inc.
Instructor name
Class Title, Term/Semester, Year
Institution
Introductory Psychology Concepts
Sensation

2. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Sensation: The activation of the sense organs by a source
of physical energy.
Human sensory capabilities go well beyond the basic five
senses (sight, sound, taste, smell, touch).
• We are sensitive not merely to touch but to a considerably
wider set of stimuli—pain, pressure, temperature, vibration.
• Vision has two subsystems—relating to day and night vision.
• The ear is responsive to information that allows us not only to
hear but also to keep our balance.

3. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Sensory Receptors: Specialized neurons activated by stimuli.
Ganglion
cells
Amacrine
cells
Bipolar
cells
Horizontal
cells Cone Rod
Light
Optic
nerve
fibers
(to
brain)
Back
of
eye
Ganglion
cell layer
Bipolar cell
layer
Photoreceptor
layer
Blind spot (optic disk)
Photoreceptors in the retina, the rods and cones, synapse with bipolar cells, which
in turn synapse with ganglion cells whose axons form the optic nerve.

4. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Thresholds
Absolute Threshold
• Defined as the lowest intensity at which a stimulus can be
detected 50 percent of the time.
• The lower the absolute threshold, the greater the sensitivity.
Approximate Absolute Thresholds for Humans
Sensory Modality Absolute Threshold
Vision Candle flame seen at 30 miles on a clear, dark night
Hearing Tick of a watch under quiet conditions at 20 feet
Taste 1 teaspoon of sugar in 20 gallons of water
Smell 1 drop of perfume diffused into the entire volume of
a large apartment
Touch Wing of a fly or bee falling on a person’s cheek from
a distance of 1 centimeter
Source: Based on Galanter, 1962.

5. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Thresholds
Just Noticeable Difference (JND)
• The smallest difference between two stimuli that people can
perceive 50 percent of the time.
• Weber’s law states that the difference threshold, or JND, is
directly proportional to the magnitude of the stimulus with
which the comparison is being made and can be expressed
as a Weber fraction.
• Weber’s law breaks down at extremely high and low
intensities of stimulation, but holds up reasonably well within
the most frequently encountered range.

6. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Thresholds
Signal Detection Theory
• Concerned with the factors that influence sensory judgments.
• There is no single point on the intensity scale that separates
stimulus detection from nondetection.
• People set their own decision criterion, a standard of how
certain they must be that a stimulus is present before they
will say they detect it.
• Decision criterion can change, depending on such factors as
fatigue, expectation, and the potential significance of the
stimulus.

7. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Thresholds
Subliminal Stimuli
• A subliminal stimulus is one that is so weak or brief that
although it is received by the senses, it cannot be perceived
consciously.
• Research suggests that subliminal stimuli may affect subtle
phenomena, such as perceptions and attitudes.
(Greenwald & Banaji, 1995)
• In one study, college students who were exposed to
subliminal presentations of aggressively toned words like “hit”
and “attack” later judged ambiguous behaviors of others as
more aggressive.
• They were also more likely to behave aggressively than were
participants who had been exposed to subliminal
nonaggressive words. (Todorov & Bargh, 2002)

8. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts
Parts of the Eye and Visual Pathways

9. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Light energy.
Of the full spectrum of
electromagnetic radiation,
only the narrow band between
400 and 700 nanometers (nm)
is visible to the human eye.
One nanometer equals
one 1,000,000,000th of a
meter.
Vision
Interpretation of the electromagnetic spectrum in terms of
amplitude and wavelength

10. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Visible Light.
+ The lowest visible frequency is called red, the highest is violet.
+ White light is an even distribution of all visible light.
+ Black is the absence of light.
Hue, Saturation, and Brightness.
+ Hue is the actual color. It is measured in angular degrees
counter-clockwise around the cone starting and ending at
red=0 or 360.
+ Saturation is the purity of color, measured in percentage from
the center of the cone (0) to the surface (100).
+ Brightness is measured in percent from black (0)
to white (100).
Source: http://www.tomjewett.com
Vision
Light, color (hue), brightness, and saturation

11. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts
Vision

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Introductory Psychology Concepts: Sensation
Lens
Ciliary muscles
Pupil
Cornea
Iris
Fovea
Optic nerve
to the brain
Blind spot
(optic disk)
{
Retina
Vision
Parts of the eye

13. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The iris regulates the size of the pupil.
Lens
Ciliary muscles
Pupil
Cornea
Iris
Fovea
Optic nerve
to the brain
Blind spot
(optic disk)
{
Retina
Vision
Parts of the eye

14. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Optic nerve
to the brainLens
Ciliary muscles
Pupil
Cornea
Iris
Fovea
Blind spot
(optic disk)
{
Retina
Vision
Parts of the eye

15. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The retina contains the rod and cone photoreceptor cells.
Lens
Ciliary muscles
Pupil
Cornea
Iris Retina
Fovea
Blind spot
(optic disk)
{
Optic nerve
to the brain
Vision
Parts of the eye

16. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The image entering the eye is reversed by the lens and cast on the retina.
Lens
Ciliary muscles
Pupil
Cornea
Iris
Fovea
Blind spot
(optic disk)
{
Optic nerve
to the brain
Retina
Vision
Parts of the eye

17. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The optic disk, where the optic nerve exits the eye, has no receptors and
produces a blind spot, as demonstrated in the enlarged view below.
Ganglion
cells
Amacrine
cells
Bipolar
cells
Horizontal
cells Cone Rod
Light
Optic
nerve
fibers
(to
brain)
Back
of
eye
Ganglion
cell layer
Bipolar cell
layer
Photoreceptor
layer
Blind spot (optic disk)
Vision
Parts of the eye

18. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Introductory Psychology Concepts: Parts of the Eye and Visual Pathways
Identify the structures of the human
eye and describe their functions.

19. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Introductory Psychology Concepts: Parts of the Eye and Visual Pathways
Identify the structures of the human
eye and describe their functions.

20. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Introductory Psychology Concepts: Parts of the Eye and Visual Pathways
Identify the pathways for visual
stimulation and describe the
brain’s role in visual information
processing.

21. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Introductory Psychology Concepts: Parts of the Eye and Visual Pathways
Identify the pathways for visual
stimulation and describe the
brain’s role in visual information
processing.

22. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Introductory Psychology Concepts: Parts of the Eye and Visual Pathways
Identify the pathways for visual
stimulation and describe the
brain’s role in visual information
processing.

23. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The Young-Helmholtz trichromatic
theory proposed three different
receptors, one for blue, one for
green, one for red.
The ratio of activity in the three types
of cones yields our experience of a
particular hue, or color.
Vision
Two classic theories of color vision:
1: Young-Helmholtz trichromatic theory (three types of cones)

24. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Hering’s opponent-process theory also
assumed that there are three different
receptors: one for blue-yellow, one for
red-green, one for black-white.
Each of the receptors can function in
two possible ways, depending on the
wavelength of the stimulus.
Again, the pattern of activity in the
receptor yields our perception of the
hue.
Vision
Two classic theories of color vision:
2: Hering’s opponent-process theory (red-green and blue-yellow
cones)

25. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
These dotted figures are used to test for
color-deficient vision.
The left one tests for blue-yellow color
blindness, the right one for red-green
color blindness.
Because the dots in the picture are of
equal brightness, color is the only
available cue for perceiving the numbers
in the circles.
Vision
Color Blindness
+ Trichromats: people with normal color vision
+ Dichromats: deficient in the blue-yellow system, the red-green system,
or both. (Approximately 7% of the male population and 1% of the
female population are dichromats.)
+ Monochromats: sensitive only to the black-white system,
totally color-blind.

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Introductory Psychology Concepts
Perception

27. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
1. Stimulus is
received by
sensory receptors.
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.

28. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
1. Stimulus is
received by
sensory receptors.
2. Receptors
translate stimulus
properties into
nerve impulses
(transduction).
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.

29. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
2. Receptors
translate stimulus
properties into
nerve impulses
(transduction).
3. Feature
detectors analyze
stimulus features.
1. Stimulus is
received by
sensory receptors.
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.

30. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
2. Receptors
translate stimulus
properties into
nerve impulses
(transduction).
3. Feature
detectors analyze
stimulus features.
4. Stimulus features
are reconstructed
into neural
representation.
1. Stimulus is
received by
sensory receptors.
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.

31. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
2. Receptors
translate stimulus
properties into
nerve impulses
(transduction).
3. Feature
detectors analyze
stimulus features.
4. Stimulus features
are reconstructed
into neural
representation.
1. Stimulus is
received by
sensory receptors.
5. Neural representation
is compared with previously
stored information in brain.
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.

32. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
PerceptionSensation
Introductory Psychology Concepts : Perception
Perception
Giving Meaning to Sensation.
The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.
2. Receptors
translate stimulus
properties into
nerve impulses
(transduction).
3. Feature
detectors analyze
stimulus features.
4. Stimulus features
are reconstructed
into neural
representation.
1. Stimulus is
received by
sensory receptors.
5. Neural representation
is compared with previously
stored information in brain.
6. Matching process
results in recognition
and interpretation of
stimulus.

33. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
One stimulus, two perceptions
This reversible figure illustrates
alternating figure-ground relations.
It can be seen as a vase,or as two
people facing one another.
Whichever percept exists at the
moment is seen as figure against
background.
Perception
Gestalt Principles of Perceptual Organization: organizing the
separate parts of our perceptual field into a unified and
meaningful whole
Introductory Psychology Concepts : Perception

34. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Each principle causes
us to organize stimuli
into wholes that are
greater than the sums
of their parts.
Perception
Gestalt Principles of Perceptual Organization
Organizing the separate parts of our perceptual field into a unified and
meaningful whole.
Figure-ground relationships
Tendency to organize stimuli into a central or foreground figure and a
background.
Gestalt perceptual laws
A series of principles that describe how we organize bits and pieces of
information into meaningful wholes.
Gestalt is the German term for “pattern”, “whole”, or “form”.
Introductory Psychology Concepts : Perception

35. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Perception
Perceptual Constancies: allowing us to recognize familiar
stimuli under varying conditions
Shape constancy
Allows us to recognize people and other objects from many different
angles.
Brightness constancy
The relative brightness of objects remains the same under different
conditions of illumination (full sunlight and shade).
Size constancy
Perception that the size of objects remains relatively constant even
though images on our retina change in size with variations in distance.
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
Patterns of light and shadow can
serve as monocular depth cues.
Drawing Hands, by M.C. Escher
Monocular depth cues
(requiring only one eye):
Patterns of light and shadow
Typically used by artists to create
perceptions of depth in their pictures.
Linear perspective
The perception that parallel lines
converge as they recede into the
distance.
Interposition
Objects closer to us may cut off part of
our view of more distant objects.
Perception
Depth Perception: translating two-dimensional information
(length and width) into three-dimensional perceptions.
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
Texture gradient
The texture or grain of an object appears finer as distance increases.
Clarity
We can see nearby hills more clearly than ones that are far away.
Relative size
Looking at two objects of similar size, the one that looks smaller will be
judged to be farther away.
Height in the horizontal plane
A ship 5 miles offshore appears to be in a higher plane and closer to the
horizon than does one that is only 1 mile from shore.
Perception
Depth Perception: Monocular depth clues (continued)
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
Motion parallax
Tells us that if we are moving, nearby objects appear to move faster in
the opposite direction than do far-away ones.
Like other monocular cues, motion provides us with information we can
use to make judgments about distance and therefore about depth.
Perception
Depth Perception: Monocular depth clues (continued)
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
1
2
3
4,5
6
7
7 monocular depth
cues are used in this
mural to create a
3-dimensional depth
effect.
1 : Linear perspective
2 : Relative size
3 : Height in the
horizontal plane
4, 5 : Texture and clarity
6 : Interposition
7 : Light and shadow
Mississippi River flood wall, Cape Girardeau, Missouri
Perception
Depth Perception: Monocular depth clues (continued)
Introductory Psychology Concepts : Perception

40. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
View-Master slides use the
principle of binocular disparity to
create the perception of depth.
Binocular disparity
Each eye sees a slightly different image.
Convergence
Produced by feedback from the muscles
that turn your eyes inward to view a close
object.
Perception
Depth Perception: Binocular depth cues (require both eyes):
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
The power of context is
shown in this figure.
Note how the B and the
13 are identical.
(Source: Coren & Ward, 1989.)
Perception
Factors Affecting Perception:
Top-down processing
Perception that is guided by higher-level knowledge, experience,
expectations, and motivations.
Top-down processing is illustrated by the importance of context in
determining how we perceive objects.
Introductory Psychology Concepts : Perception

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Introductory Psychology Concepts: Sensation
Concept, Expectation
Guides, analysis
Interpretation of incoming stimuli
Combination and interpretation of “whole”
Breakdown/analysis of stimuli
Detection of individual stimulus elements
BOTTOM-UP PROCESSING TOP-DOWN PROCESSING
Perception
Factors Affecting Perception:
Bottom-up processing
Perception that consists of the progression of recognizing and
processing information from individual components of a stimuli and
moving to the perception of the whole.
Top-down and bottom-up processing occur simultaneously and interact
with each other in our perception of the world around us.
Introductory Psychology Concepts : Perception

43. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
Perception
Visual Illusions: compelling but incorrect perceptions.
Physical stimuli that consistently produce errors in perception.
The Parthenon looks perfectly
straight, with right angles at
every corner.
Introductory Psychology Concepts : Perception

44. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
b.
Perception
Visual Illusions: compelling but incorrect perceptions.
Physical stimuli that consistently produce errors in perception.
The Parthenon looks perfectly
straight, with right angles at
every corner.
However, if had been built with
true right angles, it would have
looked as it does in figure (b).
Introductory Psychology Concepts : Perception

45. © The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Sensation
The Parthenon looks perfectly
straight, with right angles at
every corner.
However, if had been built with
true right angles, it would have
looked as it does in figure (b).
To compensate for this illusion,
the Parthenon was designed to
have a slight upward curvature
as shown in (c).
(Source: Coren & Ward, 1989, p.5.)
b.
Perception
Visual Illusions: compelling but incorrect perceptions.
Physical stimuli that consistently produce errors in perception.
c.
Introductory Psychology Concepts : Perception