Subitizing sets and set-based selection:

Early visual features determine what countsJustin Halberda, The Johns Hopkins University

Introduction

Halberda, Sires & Feigenson (2006) found that approximately

three spatially-overlapping sets can be attended, enumerated,

and stored in parallel. When briefly shown dot arrays adults canapproximate the total number of dots, the # of reds & the # of

blues (3 sets in parallel). This motivates the following questions:

1) Do sets function as individuals for attention?

2) Is there a visual continuum between individual items and sets?

3) Which features support set selection?

Question 1: Do sets function as individuals

for subitizing?! Adults (N=12) attempted both data-limited (% correct) and free-

viewing (RT) subitizing of individual dots and colored sets.

Answer: Yes

dots

Dots (1-8) Sets (1-8)How many dots? VS How many colors?

Question 2: Is there a visual

continuum between dots and sets?

“I can’t remember.

Which one is the pizer?”

Answer: Yes

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ReferenceHalberda, J., Sires, S. F. & Feigenson, L. (2006). Multiple spatially overlapping sets

can be enumerated in parallel. Psychological Science, 17(7), 572-576.,

Discussion

General Discussion• An entire set of items function as a single individualfor attention as evidenced by subitizing of sets and

early feature-based selection

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Subitizing individual

dots and subitizing

sets may draw on acommon mechanism

as indicated by

significant correlations

across these blocks as

a function of # oftargets

Question 3: Which features support

set selection?

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Answer:

G34 803

VSS, 2007

Ready

Screen

Target

1000ms

Screen 1

250ms

Screen 2

250ms

Response

0

20

40

60

80

100

1 2 3 4 5 6 7 8

Number Of Colors

0

2000

4000

6000

8000

Response T

ime (

ms)

0

20

40

60

80

100

Percent E

xactly

Correct

0

20

40

60

80

100

Percent

Exactly C

orrect

0

20

40

60

80

100

1 2 3 4 5 6 7 8

Number Of Colors

0

1000

2000

3000

Re

sp

on

se

Tim

e (

ms)

! Adults can subitize setssets

1 2 3 4 5 6 7 8

0

25

50

75

100

0

2250

4500

6750

9000

1 2 3 4 5 6 7 8

RT (

ms)

1 2 3 4 5 6 7 8

0

25

50

75

100

Complete Overlap

Some Overlap

No Overlap

Single Dots

Pe

rce

nt

Exa

ctly C

orr

ect

Number Of Colors

Limited-Viewing Free-Viewing

! Adults (N=12) attempted both data-limited (% correct)

and free-viewing (RT) subitizing of four display types

! Tthese four display types varied the spread of thesubsets (how distributed the sets are) and the distance

between the centroids of the subsets

! The centroid may represent the position of a set in

space and therefore separation in centroids may be

crucial for subitizing

+ = Centroid O = Spread

++ +

+

+

+

++

+

Complete

Overlap

Some

Overlap

No

Overlap

Single

Dots

Size

Gabor

Color

Curvature

Orientation

Vernier

ConjunctionShape

Target Target

The usual

suspects

40

50

60

70

80

90

100

Perc

ent

Corr

ect

±SE (

chance=

50%

)

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Co

lor

Cu

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ture

Ori

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Ve

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Co

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nc

tio

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Sh

ap

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! Adults (N=12)enumerated a target set

among distractors

! Task: Which screen

(1st or 2nd) has moretargets?

! Subitizing capacity increased smoothly up to a level of

3-4 subsets in parallel as a function of increasing

centroid distance and decreasing spread

1 3 5 1 3 5

R2 = 0.414

R2 = 0.4893

R2 = 0.0774

R2 = 0.1434

R2 = 0.1555

R2 = 0.149

R2 = 0.118

R2 = 0.0972

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1000 2000 3000

Subject RTs For Individual Dots (ms)

Subje

ct

RTs F

or

Colo

red S

ets

(m

s)

Answer = 1

Answer = 2

Answer = 3

Answer = 4

Answer = 5

Answer = 6

Answer = 7

Answer = 8