perception & pattern recognition ii. today’s agenda: turn in coglab assignment #1 today’s...
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Perception & Pattern
Recognition II
Today’s agenda:
Turn in CogLab Assignment #1 Today’s theme: Perception is active
More examples from Reed, Chapter 2 Finish up perceptual illusions
Next Tuesday: Face Recognition
What do you see?
Perception is active, not passive.
PERCEPTION
Sensory input
Perception is active, not passive.
Knowledge, expectations(Top-down processing)
PERCEPTION
(Bottom-up processing)
Sensory input
During perception, information is:
Omitted Decomposed into features Added Categorized Organized Distorted
The Whole Report Procedure
An array of 12 letters is BRIEFLY flashed onto the screen.
After it’s removed, the observer tries to report what they saw.
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T M F W
L R E P
A X C O
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L A P C
K R Z D
O S V Y
The Whole Report Procedure
An array of 12 letters is BRIEFLY flashed onto the screen.
After it’s removed, the observer tries to report what they saw.
People can typically report only 3-4 of the 12 letters. Does this really mean that only 4 letters made it into
perception? Sperling invented the Partial Report Procedure, which
answered this question.
The Partial Report Procedure (Sperling, 1960)
The subject fixates on a cross; then letters flash onto the screen just long enough to cause a visual afterimage.
High, medium, and low tones right after the letters are removed signal which row of letters to report.
(Fig. 2.11, p. 31).
The information available in brief visual presentations (Sperling, 1960)
If the delay (after the display disappears and before the cueing tone) is short, people can report all or almost all letters in the row they’re cued to report!
What does this mean?
Reed Fig. 2.12 (p. 32)
Evidence for sensory memory (Sperling, 1960)
After the display is removed, people can continue to “read” letters off their visual icon if (and only if) they’re able to focus attention on the cued row before the icon fades.
Sperling’s discovery led to the idea of an extremely short-lived visual icon (visual sensory store) with unbounded capacity.
Without attention, information in the visual icon (VSS) is rapidly lost.
(Reed, p. 3, Figure 1.1)
During perception, information is:
Omitted Decomposed into features Added Categorized Organized Distorted
Feature integration theory
(Treisman & Gelade, 1980)
The popout phenomenon, discovered by Anne Treisman
This provides more evidence for low-level features, perceived automatically.
For the next slide, try to react as quickly as possible.
You’ll see a field of black 0’s. Slap the desk IF (and only if) you see
the letter V in the field of 0’s.
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 V 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Straight lines pop out in a field of curved lines.
This task is pre-attentive (doesn’t demand attention).
Let’s try it again. Slap if you see a V.
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 V 0 0 0 0
Popout happens fast, regardless of the size of the display!
This means you’re searching it all at once - in parallel.
Let’s try it again. Slap if you see a V.
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Straight lines pop out from curved lines, and vice versa.
What about angular orientation? In this next field of vertical lines, slap the desk if you see a slanted line.
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Now for color.
Slap if you see something red.
O N N N O O O N N O N O N N N O O N
O O O N O O O N N O N N N O O N O O
N O O N O O N O O N N O O O O N O N
O N O N O N O O O N O N O N N N O O
N O O N O O O N N O O N O N N O N N
O N N N O O O N N O N O N N N O O N
N O N O O O N O N O N N N O O N O O
We know that color pops out, and so does curvature.
For the next slide, slap the desk if (and only if) you see a red O.
O O O N O O O N N O N N N O O N O O
N O O N O O N O O N N O O O O N O N
O N O N O N O O O N O N O N N N O O
O N N N O O O N N O N O N N N O O N
N O N O O O N O N O N N N O O N O O
N O O N O O O N N O O N O N N O N N
O N N N O O O N N O N O N N N O O N
And again: Red O.
N N O
O N O
One last time:
O N N N O O O N N O N O N N N O O N
O O O N O O O N N O N N N O O N O O
N O O N O O N O O N N O O O O N O N
O N O N O N O O O N O N O N N N O O
N O O N O O O N N O O N O N N O N N
O N N N O O O N N O N O N N O N O N
N O N O O O N O N O N N N O O N O O
Conjunction search Searching for a conjunction of features takes
longer! You must search one at a time (serially) rather than in parallel (all at once).
For conjunction search, the display size (set size) matters, since you have to search every item for the particular combination of features.
X
T
TT
X
T
TX
T TX
X
T
T
Another demonstration of set size (find the white vertical bar)
1 Distractor
12 Distractors
29 Distractors
Parallel vs. serial processesSerial process•Process each object, one at a time•The time it takes depends on # of objectsParallel process: •Process multiple things at once or “in parallel”•The number of objects doesn’t matter -
it’s equally fast, whether there aremany or few objects.
•Works for limited kinds of things
Sperling: We recognize letter in parallel butreport them serially.
Illusory conjunction at the preattentive stage
Next, I will briefly flash a string of black numbers and colored letters. Try to report the number at the beginning AND the number at the end of the string.
2 X T O 8
What numbers did you see?
What numbers did you see? Now what were the letters? What color were they?
Illusory Conjunction Effect
Illusory Conjunction (Treisman & Schmidt, 1986) People report incorrect combinations of features
about 30% of the time. due to lack of time to focus attention. They recognize T and blue, but these features
are “floating” - This effect is pre-attentive Attention is needed to “glue” features together!
(binding)
Without attention, information in the visual icon (VSS) is rapidly lost.
(Reed, p. 3, Figure 1.1)
During perception, information is:
Omitted Decomposed into features Added Categorized Organized Distorted
Information is added
Knowledge, expectations(Top-down processing)
PERCEPTION
(Bottom-up processing)
Sensory input
Information is added
The blind spot Speech perception with noise
Information is added
I knew that the *eel was on the
orange
axle
shoetable
The phonemic restoration effect
(Warren & Warren, 1970)
Context helps us perceive speech
Reading words with noise
Word Superiority Effect (Reicher, 1969)
When is a given letter recognized fastest: alone, in a word, or in a non-word?
K WORK ORWK
Word Superiority Effect (Reicher, 1969)
Respond:
D or K?
(Fig. 2.13, p. 35)
Brief display Mask & choice
Word Superiority Effect (Reicher, 1969)
Respond:
D or K?
(Fig. 2.13, p. 35)
Brief display Mask & choice
Word Superiority Effect (Reicher, 1969)
Respond:
D or K?
(Fig. 2.13, p. 35)
Brief display Mask & choice
Word Superiority Effect (Reicher, 1969)
Respond:
D or K?
(Fig. 2.13, p. 35)
Word superiority effect: An interactive activation model
Word level
Letter level
Feature level
Input
See Reed, p. 36 - in addition to
activation, there’s also inhibition.
Neural network models
PDP - parallel distributed processing Nodes - processing units used to
abstractly represent elements such as features, letters, and words
Links, or connections between nodees Activation - excitation or inhibition that
spreads from one node to another
During perception, information is:
Omitted Decomposed into features Added Categorized Organized Distorted
Information is categorized
The input to perception is continuous, but the output is categorical.
Reed, Fig. 2.1 (p. 18)
Variations in handwriting (Chapanis,1965)
Despite variation, letters and wordsare still categorized.
The same squiggle may be categorized differently in different contexts.
Speech perception is categorical
Can we tell very similar sounds apart? It depends! Example: Voicing: when vocal folds vibrate Early VOT (voice onset time) Late VOT
/p/ /b/
/g/ /k/ Expt: Subjects hear /ga/ - /ka/ sounds, judge if
each is “ga” or “ka”; voicing varies slightly. Then % “ga” judgments is graphed for each VOT
Speech perception is categorical If we perceived what was actually out there in the
world, what would the graph look like?
Speech perception is categorical Surprise! People perceive sounds that vary
continuously as suddenly in a different category.
Speech perception is categorical Discriminating between sounds that differ by only
10 ms in their VOT: Performance peaks at the boundary.
(Note: Task is to judge 2 sounds as “same” or “different”)
Categorical perception
Helps us categorize information quickly Helps us ignore irrelevant information
For speech sounds, the same amount of difference - say, 20 ms - leads to very different results, depending on whether it falls within or between phonetic categories
During perception, information is:
Omitted Decomposed into features Added Categorized Organized Distorted
Information is organized
(For example, Gestalt properties of perception - see last lecture.)
Information is distorted
We don’t see what’s out there in the real world - we see what our perceptual system biases us to see.
Muller-Lyer illusion Ponzo illusion Ames room Moon illusion Relative size illusion
Perceptual illusions result from the helpful biases of constancy, depth perception cues, and Gestalt principles!
Perceptual illusions
Muller-Lyer Illusion
Ponzo Illusion
Ames Room
Ames Room
Moon Illusion
Relative height
Higher objects on the ground are seen as farther away
Lower objects in the sky are seen as farther away
Relative size illusion
Conclusions about perception
Perception is not passive; percepts are actively constructed by the system.
Perception uses both bottom-up and top-down information.
During perception, information may be omitted, added, decomposed, categorized, organized, or distorted.