Personlige og fundamentale egenskaber i synsprocessen. Transformation af stimulusenergi til perception.

1. Psykofysik
Transformation
af stimulusenergi til perception
Torben Helstrup
Neurooptometrist FCOVD (MSc)

2. Helikopter view
Objektiv distance
• Hjerneforskning: Scanning,
dyreforsøg, eksperimenter
• Hjerneskader: Krige, ulykker
• Psykofysik: Sanseegenskab.
• Lodtrækningsforsøg
• Faghistorik
• Tidens bedste
viden/forståelse
• Beslutningsgrundlag
Subjektiv indlevelse
• Personlige egenskaber
• Uddannelse, kurser
• Mentorlæring
• Subspecialisering
• Erfaring (egen og andres)
• Tidens bedste behandling
• Dømmekraft

3. Sensation & Perception
OBS ! Alt sakset fra Slideshare

4. Terminology
• Sensation: the process by which sensory
receptors receives stimulus energy from our
environment
• Perception: the process of organizing &
interpreting sensory information

5. 5
Organizational Behavior /
Perception
The Perceptual Process
1. Sensation
– An individual’s ability to
detect stimuli in the
immediate environment.
2. Selection
– The process a person
uses to eliminate some of
the stimuli that have
been sensed and to retain
others for further
processing.
3.Organization
– The process of placing
selected perceptual
stimuli into a framework
for “storage.”
4.Translation
– The stage of the
perceptual process at
which stimuli are
interpreted and given
meaning.

6. SENSES
The mechanisms which convert stimulus energy
into neural energy
5 PRIMARY SENSES:
1. Vision
2. Hearing
3. Smell
4. Taste
5. Skin senses
In addition, we have
6. Kinaesthetic
7. Sense of Equilibrium

7. • Focuses on ways in which we translate
physical events such as light and sounds
into psychological experiences.
Psychophysics

8. • the weakest amount of a stimulus
that a person can distinguish from
no stimulus at all 50% of the time.
Examples of Absolute Threshold
Vision: candle flame viewed from about
30 miles on a clear, dark night.
Hearing: a watch ticking from about 20 feet away in a
quiet room.
Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.
Smell: about one drop of perfume diffused throughout a
small house (1 part in 500 million).
Touch: the pressure of the wing of a fly falling on a cheek
from a distance of about 0.4 inch.
Absolute Threshold
Gustav Fechner

9. • the minimum difference in magnitude of two
stimuli required to tell them apart 50% of the
time.
• Similar to the just noticeable difference (jnd)
Weber found that for:
• Light – 2%
• Weight – 2%
• Constant pitch – 1%
Difference Threshold
Ernst Weber

10. • Considers the human aspects of sensation,
and perception
• Assumes that the relationship between a
physical stimulus and a sensory response is
not just mechanical.
• Other factors include:
– Training (learning)
– Motivation (desire to perceive)
– Psychological states such as fatigue or alertness, or
focusing on signals one feels important
i.e. a babies cry
Signal-Detection Theory

11. • Brain cells that respond to different aspects
of features of a scene (e.g. angles, vertical,
horizontal).
Feature Detectors in the Brain

12. Visual Information Processing
Processing of several aspects of the stimulus
simultaneously is called parallel processing. The
brain divides a visual scene into subdivisions such
as color, depth, form, movement, etc.

13. • Size constancy:
– Allows us to perceive objects to be the same size even
when viewed from different distances.
– Experiences teach us about perspective.
• Color constancy:
– The tendency to perceive objects as retaining their
color even though lighting conditions may alter their
appearance.
• Brightness constancy:
– similar to color constancy.
• Shape constancy:
– The tendency to perceive objects as maintaining their
shape, even if we look at them from different angles so
that the shape of their image on the retina changes
dramatically.
Perceptual Constancies

14. Figure 4.20 Shape Constancy. When closed, this door is a rectangle. When open, the retinal image is
trapezoidal. But because of shape constancy, we still perceive it as rectangular.
Shape Constancy

15. Figure 4.20 Shape Constancy. When closed, this door is a rectangle. When open, the retinal image is
trapezoidal. But because of shape constancy, we still perceive it as rectangular.
Shape Constancy

16. Perceptual Constancy
• Color Constancy
– An object in perceived as having roughly the same color
regardless of the light source illuminating it.

17. Compare Darkness
Edward H. Adelson Checker Shadow Illusion

18. Compare Darkness
Edward H. Adelson Checker Shadow Illusion

19. Compare Darkness
Edward H. Adelson Checker Shadow Illusion

20. Perceptual Constancy
• Size Constancy
–Objects are perceived to have the same size no
matter how far it is from us.
Point A
Point B

21. Size-Distance Relationship
Both 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

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

23. Which one is bigger?
Ponzo Illusion

24. Which one is bigger?
Ponzo Illusion

25. Which one is bigger?
Ponzo Illusionhttp://www.youtube.com/watch?v=hdZHfzjJf-g

26. Which one is bigger?
Ebbinghaus Illusion
Hermann Ebbinghaus
1850-1909

27. 28
Organizational Behavior /
Perception
Figure-Ground Illustration
•Field-ground differentiation
– The tendency to distinguish
and focus on a stimulus that
is classified as figure as
opposed to background.

28. Figure 4.13 The Rubin Vase. A favorite drawing used by psychologists to demonstrate figure–ground
perception. Part A is ambiguous, with neither the vase nor the profiles clearly the figure or the ground. In
part B, the vase is the figure; in part C, the profiles are.
The Rubin Vase

29. Figure 4.14 Necker Cube. Ambiguity in the drawing of the cube makes perceptual shifts possible.
Therefore, the darker tinted surface can become either the front or back of the cube.
Necker Cube

30. GROUPING
• 1. The Principles of Similarity
– Stimuli which are similar tend to be
perceived as a forming group.

31. GROUPING
• 2. The Principle of Proximity
Objects near each other tend to be seen as a
group or a unit.

32. GROUPING
3. The Principle of Closure
-When fragmentary stimuli form enough of a
familiar figure, we tend to perceive the whole
figure, ignoring the missing parts of parts

33. GROUPING
• 4. The Principle of Continuity
– The stimuli which form a continuos pattern are
perceived as a whole, the pattern they make
generally appears as a figure apart from the
ground.

34. 35
Organizational Behavior /
Perception

35. Volunteer?
• Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it
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are, the olny iprmoatnt tihng is taht the frist and
lsat ltteer be at the rghit pclae. The rset can be a
toatl mses and you can sitll raed it wouthit a
porbelm. Tihs is bcuseae the huamn mnid deos not
raed ervey lteter by istlef, but the wrod as a wlohe.

36. Depth Perception
Visual Cliff
Depth perception enables us to judge distances.
Gibson and Walk (1960) suggested that human
infants (crawling age) have depth perception. Even
newborn animals show depth perception.
Innervisions

37. • Monocular Cues: cues that can be
perceived by one eye.
– Perspective:
• distances between far off objects appear to be smaller than
equivalent distances between nearby objects.
– Relative size:
• the fact that distant objects look smaller than nearby objects of
the same size.
– Clearness of an object:
• We sense more details of nearby objects.
– Interposition:
• Nearby objects can block our view of more distant objects.
• Interposition is placing of one object in front of another.
Depth Perception

38. Figure 4.17 The Effects of Interposition. The four circles are all the same size. Which circles seem
closer? The complete circles or the circles with chunks bitten out of them?
Effects of Interposition

39. • Monocular Cues continued. . .
– Shadows:
opaque objects block light and produce shadows giving us a
relationship to the source of light
– Texture Gradient:
close objects are perceived as having rougher textures
– Motion Parallax:
the tendency of objects to seem to move backward or forward as a
function of their distance
Depth Perception

40. Figure 4.18 Shadowing as a Cue for Depth. Shadowing makes the circle on the right look three-
dimensional.
Shadowing as a cue for depth

41. • Binocular Cues: cues that can be perceived
by both eyes.
– Retinal disparity:
• The difference between projected images (e.g. different angles).
• Closer objects have greater retinal disparity.
– Convergence:
• Causes feelings of tension in the eye muscles and provides
another binocular cue for depth.
Depth Perception

42. Personal Factors in Perception
• The way we perceive objects is greatly
determined by personal factors such as
motives, emotions, attitudes and frame or
reference.
• A change in our frame of reference will change
the way we perceive an object.
– A frame of reference as as system of related
categories in terms which judgements are made.
(Sartain)

43. ATTENTION and PERCEPTION
• We select certain objects to perceive while
ignoring others. This is called the perceptual
focusing, attention.
(Hilgard, 1971)
• Attention is the direction of perception toward
certain selected objects.
(Sartain, 1967)

44. “ WE DON’T SEE THINGS AS THEY ARE,
WE SEE THINGS AS WE ARE.”

45. 46
Organizational Behavior /
Perception
Receiving Stimuli
(External & Internal)
Selecting Stimuli
External factors : Nature,
Location,Size,contrast,
Movement,repetition,similarity
Internal factors : Learning,
needs,age,Interest,
Organizing
Figure Background ,
Perceptual Grouping
( similarity, proximity,
closure, continuity)
Response
Covert: Attitudes ,
Motivation,
Feeling
Overt: Behavior
Perceptual Process
Interpreting
Attribution ,Stereotyping,
Halo Effect, Projection

46. Selective Attention
• http://www.youtube.com/watch?v=vJG698U2Mvo
• http://www.youtube.com/watch?v=Ahg6qcgoay4

47. Khan academy
• https://www.khanacademy.org/science/healt
h-and-medicine/nervous-system-and-sensory-
infor/sensory-perception-2014-03-
27T18:45:20.451Z/v/perceptual-organization
• Sansefysiologi:
http://www.tutis.ca/Senses/index.htm