PERCEPTION AND PATTERN RECOGNITION

• Making sense of sensation– Local vs. Global scope– Data-driven (sensory, bottom-up) vs.

Concept-driven (knowledge, “top-down”)

• Organizing the perceptual world– Gestalt “strategies” of grouping

• Recognizing familiar patterns– Changes in performance and process as

we practice

• Impairments of pattern recognition skill

GESTALT “STRATEGIES” OF PATTERN ORGANIZATION

PROXIMITY

SIMILARITY

CONTINUITY

CLOSURE

ASYMMETRIES INHEMISPHERIC PROCESSING

One hypothesis:

Left Hemisphere specialized for “local detail,” fine-grained analysis

Right Hemisphere specialized for “global form” and wide scope

Damaged LH Damaged RH

• vast number of distinct patterns can be learned– e.g., over 60,000 spoken or written

words

• recognition can with practice by very fast and “automatic”– e.g., Lexical Decision Speed

BLACK ? ~600 msec

BLARK

• can succeed in spite of great variability of input (“noise”)

SOME BASIC FACTS ABOUTHUMAN PATTERN RECOGNITION

PRACTICE AND PATTERN RECOGNITION SKILL

• speed and accuracy improve

• requires less attention and effort

• becomes more “noise resistant”

• “distinctive” features are learned

• “prototype” patterns may be learned

• larger “units of recognition” emerge

• skill, and impairment, are “domain-specific”

THE POWER LAW OF PRACTICE

Speed and accuracy improve,but at an ever-slower rate

Task: reading inverted text (Kolers, 1975)

Time = 10 x practice a -b

1

4

7

10

13

16

19

min

/pa

ge

2 4 8 16 32 64128

# of pages read (LOG)

1

10

100

min

/pa

ge

(L

OG

)

2 4 8 16 32 64128

# of pages read (LOG)

LEARNING DISTINCTIVE FEATURES OF PATTERNS

Feature Analysis: Define a small setof features whose presence andarrangement defines the patterns

FEATURESVoicing

Place ofArticulation

Voiced Unvoiced

Bilabial

Alveolar

/b/ /p/

/d/ /t/

e. g.: consonant phonemes

Fig. 3-17, p. 69

FEATURES and RELATIONSRecognizing Objects by Components(Biederman’s RBC model)

ABSTRACTING THE ”TYPICAL” PATTERN (PROTOTYPE)

Task: learn to categorize faces: (Reed, ‘72)

Category 1

Category 2

Then tested on old and new faces:

P2 P1

EVIDENCE FOR PROTOTYPE ABSTRACTION (Reed, 1972)

• “Studied” prototypes are classified more quickly and accurately than other studied patterns

• Even if prototype had not been studied,– it was still the easiest to classify– and was often falsely identified as

“studied” in an old/new decision

Reed Biederman

CARICATURES:Exaggerating distinctive features

Celebrity caricatures atAbout Faces

PRINTED WORDS AS UNITS OF PATTERN RECOGNITION

Task: letter detection

WARM WBPM ###MOR OR30 MSEC

Then…(1 sec)

M#$%& N

Reicher (1969): where unitizing helps

70%C 58%C 62%C

Johnson (1987): where unitizing hurts

“is first letter an “R”?

BEAN faster than BEAR

but BFXN equal to BFXR

STIMULUS FEATURES AND SENTENCE CONTEXT(Rueckl & Oden, 1986)

Task: read sentence contexts,

The { lion tamer / dairy farmer } raised ____ to supplement his income.

then. .

0

20

40

60

80

100

% s

ee

ing

{b

ea

r}

Stimulus feature (in bea_s)

Dairy Farmer

Lion Tamer

bearsbeans . . . . . . .

IMPAIRMENTS OF PATTERN RECOGNITION SKILL

• Skills, and impairments, tend to be “domain-specific” to codes or modality:– ALEXIA WITHOUT AGRAPHIA

• can’t read, but can write– PROSOPAGNOSIA

• can’t recognize familiar faces

–MOTION AND COLOR AGNOSIA

•objects appear still, or “grey”–AMUSIA

•can’t recognize/match familiar melodies

DEVELOPMENTAL DYSLEXIA

• defined as a selective slowness in reading acquisition and speed

• estimates range from 2% to 10% of school population

• similar numbers of boys and girls

• not a problem of visual perception

• perceiving and representing rapid sequences of speech sounds

• predicted by “phonological awareness” tests

• reading and complex phonology remain problems into adulthood