perception & pattern recognition ii. today’s agenda: turn in coglab assignment #1 today’s...

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.