1. Perception

2. Question of the Day
Why is recognizing an object so easy for humans, but so difficult for computers?

3. Points of Confusion Points of confusion Stimulus ambiguous
Objects overlap, Parts of objects may be hidden/blurred
Differences in lightness/darkness could be from more than one cause

4. Perception: attaching meaning to incoming sensory information What is
this?

5. Template matching Bottom-Up Processes
Bottom-up processes: start with units/elements and put them together, but no way to go back and correct/change perception
Top-down: expectations influence what we see, where we look, how you put information together
The number “4” from the check is compared to a list of stored templates.

6. Bottom-Up Processes Problems with Template Matching
Large number of stored templates needed
How are new templates made?
An object can be “more or less” like the template
We can recognize many variations of a template
Problems with Template Matching
Large number of stored templates needed
How are new templates made?
An object can be “more or less” like the template
We can recognize many variations of a template

7. Bottom-Up Processes Figure 2-8
Humans probably do not use this much, if at all; world just isn’t made up of objects that exactly match templates
Figure 2-8

8. Bottom-Up Processes
Featural Analysis
features (“parts”) of a stimulus are recognized by feature detectors and added together to help us perceive an object
Lines or edges
Geons
Phonemes
Parts of a face (eyes, nose…)
Featural analysis: perception occurs by having us recognize parts of an object (lines/edges), which we then put together to form a whole object
Neurological evidence for it
features (“parts”) of a stimulus are recognized by feature detectors and added together to help us perceive an object
Lines or edges
Geons
Phonemes
Parts of a face (eyes, nose…)

9. Featural Analysis Geons
For geons, we look at both the shape and position of parts

10. Figure 2-14 A depiction of Selfridge’s (1959) Pandemonium model.
Featural
Analysis
Letter
detection
Figure A depiction of Selfridge’s (1959) Pandemonium model.

11. Bottom-Up Processes Featural Analysis Feature Properties
Detectors can respond at different intensities
Connections between detectors can have different strengths
It is possible to change what a detector will respond to
Problem with theory; how do you define what a good feature is, or know when to use it,

12. Bottom-Up Processes Prototype Matching
Similar to feature matching, except that the stored representation does not have to be an exact match – it is a prototype, idealized concept
In features, all parts have to match
In prototype, the more parts match, the better chance of matching with prototype
Prototype model can explain this, feature model could not

13. Bottom-Up Processes Prototype Matching http://www.palm.com
Program tries to match to a prototype

14. Figure 2-19 An example of context effects in perception.
Top-Down Processes
The bottom-up theories can’t explain why we would mistakenly see they bike
Top-down – expectations affect perceptions (context, past learning)
Figure 2-19 An example of context effects in perception.

15. Top-Down Processes Perceptual Learning
Here are some examples of top-down processing…
Perceptual learning: our perceptions can change with learning, we can get better at recognizing objects with practice, top-down processing helps us know which features of an item to focus on to remember
Task – shown original, needed to pick matching ones out of a deck, but never given feedback
After a while people got better at it,
Mistakes they made were related to number of similarities between stimuli

16. Top-Down Processes Change Blindness
Change blindness; inability to detect change in object or scene,
asking directions story (50% didn’t notice)
point here – we seem to operate by just getting gist of a scene sometimes

17. Top-Down Processes K WORK OWRK K D Word Superiority Effect
Word: Ss shown letter, either by itself or with other letters
Then asked to chose which letter they saw – K or D
Did much better with task when letter in word then when letter alone or in a nonword
OWRK

18. Bottom-Up and Top-Down Processing working together
Flying Animal
Bottom-Up and Top-Down Processing working together
_at
Word Perception
Connectionist Model
Bat
Words
Letters B
Fox
Bat
Individual letters are bottom-up (you look at each line to tell what letter it is, then each letter in order to tell what word it is)
but from top-down you also get expectations about what it should be
Ex; crossword puzzles for word bat (you have letters at and clue flying animal)
Neg and pos connections between nodes
How does this model explain word superiority?
Fat I
Features
(lines)
Rat
Cat

19. Theories of Perception
Gestalt Psychology (Wertheimer, Koffka, and Kohler – 1920s)
“The whole differs from the sum of its parts”
Perception is not built up from sensations but is a result of perceptual organization
We use heuristics to make “best guesses” about the identity of stimuli
Gestalt Psychology (Wertheimer, Koffka, and Kohler – 1920s)
“The whole differs from the sum of its parts”
Perception is not built up from sensations but is a result of perceptual organization
(lights are parts, but when at right timing look like they are moving)
(principles, or rules, for how our brain organizes information)
We use heuristics to make “best guesses” about the identity of stimuli

20. The Gestalt Approach Principles of perceptual organization
Pragnanz - every stimulus is seen as simply as possible
(a) This is usually perceived as five circles, not as the nine shapes in (b).
Principles of perceptual organization
Pragnanz (also called law of simplicity) - every stimulus is seen as simply as possible

21. Gestalt principles of Perceptual Organization
What is the simplest, most stable perception here?
Large is usually more stable than small
Another question: why do these rules come from? Do we learn them over time, are they inborn
Figure 2-5

22. Gestalt principles of Perceptual Organization
Similarity

23. Gestalt principles of Perceptual Organization
Good continuation
what most people
would see
not this
contours based on smooth continuity are preferred to abrupt changes of direction

24. The Gestalt Approach Principles of perceptual organization
Good continuation
Connected points resulting in straight or smooth curves belong together
Lines are seen as following the smoothest path
Good continuation
Connected points resulting in straight or smooth curves belong together
Lines are seen as following the smoothest path

25. Gestalt principles of Perceptual Organization
Proximity
Gestalt psychologist realized that we did not “see” what was really out there, not the way that a camera would, we add things, we tend to see patterns, as a rule we “see” whatever is simplest , most stable
Gestalt made a collection of these rules, lots, but we will only talk about a few

26. The Gestalt Approach Principles of perceptual organization
Proximity - things that are near to each other are grouped together
Proximity - things that are near to each other are grouped together
In both A and B we see horizontal lines, even though in B some circles changed into squares, and might predict that we would see vertical rows according to similarity

27. Gestalt principles of Perceptual Organization
Common fate

28. The Gestalt Approach Principles of perceptual organization
Meaningfulness or familiarity - things form groups if they appear familiar or meaningful
Meaningfulness or familiarity - things form groups if they appear familiar or meaningful
What do the red lines look like to you? Tadpoles or flames?
Students with more familiarity with these techniques will easily see the “flames” as the figure; less car-oriented students will most likely see “tadpole” shapes as the figure

29. The Gestalt Approach Principles of perceptual organization
Common region - elements in the same region tend to be grouped together
Uniform connectedness - connected region of visual properties are perceived as single unit
Synchrony - elements occurring at the same time are seen as belonging together
a. Common region - elements in the same region tend to be grouped together
(as opposed to B, where closer circles grouped together)
c. Uniform connectedness - connected region of visual properties are perceived as single unit
d. Synchrony - elements occurring at the same time are seen as belonging together
Grouping by (a) common region; (b) proximity; (c) connectedness; and (d) synchrony. The yellow lights blink on and off together.
So these principles are heuristics, best guesses, usually fast and usually right, but not always right
Sometimes perceptual system gets it wrong and we make mistakes

30. Perceptual Segregation
Properties of figure and ground
The figure is more “thinglike” and more memorable than ground
The figure is seen in front of the ground
The ground is more uniform and extends behind figure
The contour separating figure from ground belongs to the figure
Figure/ Ground and Logos: A common application of figure/ground reversals is in many company logos. For example, the FedEx logo contains an arrow between the last “E” and the “x”. Most students are unaware of this, even though they have seen the logo numerous times. Other logos that have arrows in figure/ground patterns are the logos for McLane Food Distribution ( ); and Equal Exchange ( Ravenswood Wine ( also has a reversible figure/ground stimulus as its logo: the ravens are actually less likely to be seen as the figure at first glimpse. One of the most clever examples is the Big Ten Conference logo ( ). When Penn State was added to the Big Ten conference, there were now 11 teams in the Big Ten: The logo reflects this by having the white area between the letter “T” as an “11” when seen as the figure.

31. Perceptual Segregation
Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background
Reversible figure-ground
Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background
This slide and the next one explain reversible figure-ground objects. These can be used as an example for how the viewer actually determines the figure rather than this being something that is dictated by the environment
So if you see faces, where is the figure? Blue or white space?
Gestalt approach: perception is parsing (segmenting) image into figure and ground, which equals form perception
What is Figure = the thing, the important object, easier to remember
What is ground = not important, harder to remember
Assumption of ours, that there should be figure and ground

32. Figure 5.25 (a) When the vase is perceived as figure, it is seen in front of a homogeneous dark background. (b) When the faces are seen as figure, they are seen in front of a homogeneous light background.

33. Perceptual Segregation
Previous principles all talked about how we group parts together to form a single object
But we also have to do the opposite, separate parts, distinguish one object from another one
Failing to divide figure from ground
How many of you can remember what the fedex logo looks like?
Can anyone remember what geometric sign is in the logo?

34. Gestalt principles of Perceptual Organization
Closure
Your mind supplies the missing parts if enough of the significant features are visible

35. Neuropsychological Perspective
Word Perception
Neuropsychological Perspective
Subjects shown words
All four activated primary visual cortex
For last two, more activation on left side (where words understood) and outside of pvc
Figure (p. 91) Example of stimuli used in the PET scan study of processing words.

36. Direct Perception vs. Constructivist Approach
Biological motion
Other models that we have talked about assume that person does something to incoming info to create a percept
Direct perception – another way of viewing it, person does very little to incoming info, instead
You can say that altho something may change, usually the relationships b/t parts don’t
Tune in a different scale, biological motion

37. Optic flow
Optic flow – nearer things move faster, farther things move slower

38. Direct Perception Affordances:
Information from the stimulus that specifies how it can be used
Affordances:
Information from the stimulus that specifies how it can be used
We perceive not just the object itself, but how the object might be used
We don’t just see a log, we see it as something that we could sit on, or hide behind, or burn

39. Visual Agnosia
John’s history: male, executive in energy company, 1981 had stroke, damaging occipital lobes
Afterwards could not recognize doctors, nurses, unable to read, got lost going to bathroom
When wife visited him in the hospital, she brought flowers, John had to ask what they were
When he went home he did not recognize his house
He could write his signature but had more difficulty with other writing – why do you suppose this is?
Brain scan, no initial evidence of lesion in CT scan
Later tests of visual also showed he had lost upper visual field, although he automatically shifted vision in normal everyday seeing
Agnosia (a-gnosis, "non-knowledge") is a loss of ability to recognize objects, persons, sounds, shapes or smells.

40. Visual Agnosia Associative Visual Agnosia Apperceptive Visual Agnosia
Can copy, but unaware what it is; cannot assign meaning to object
Difficulty in transferring visual info into words
Apperceptive Visual Agnosia
Cannot recognize by shape
Cannot copy drawings
Often involves ‘prosopagnosia’
Associative Visual Agnosia
Can copy, but unaware what it is; cannot assign meaning to object
Difficulty in transferring visual info into words
Apperceptive Visual Agnosia
Cannot recognize by shape
Cannot copy drawings
Often involves ‘prosopagnosia’

41. Agnosia apperceptive agnosia.
some Patients with apperceptive agnosia have difficulty recognizing this object as a chair because they cannot interpolate the missing contours.
some Patients with apperceptive agnosia would have difficulty recognizing the chair when it is viewed from this unusual angle.

42. Identification of Faces and Members of Categories Prosopagnosia
The Fusiform Face Area:
Identification of Faces and Members of Categories Prosopagnosia
At very end of ventral pathway
Prosopagnosia:
Failure to recognize particular people by the sight of their faces.

43. Perceptual Intelligence light-from-above heuristic
Percept must be meaningful, you must interpret the incoming image