Surround modulation of visual motion integration and segregation(Summary of Awarded Presentation at the 29th Annual Meeting)

(1)

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

ThejopaneseJburnalofFXychonomicSm'ence

2011,VoL 30,No.1,125-126

Summary

ofAwarded

Presentation1-203

Surround

modulation

integration

and

of

visual

motion

.

segregatlon

Hiromasa

TAKEMuRA*･

*2 _and

_Ikuya

_MuRAKAMi*

The [iniversiC),

of

7bkyo" and

ISPS

Research Feltow'2

Thc visual system integratesor segregates two motion components

in

the same

visual

fie[d

depending on directiondifference. We examined how the surrounding motion modulates such

integration

or segregation.

In

the experiment, participantswere _presented with motion compo-nents

in

two nearby

directions

{e,g.

±

45 deg

frorn

vertical).

We

found

that

participantsreported

two segregated metions more frequently when the

direction

of the surrounding motion was

equivalent to the averaged direction of centra] motions. In contrast. _participants reported one

integrated

motion when the

direction

of the surrounding motion was opposite that of the center.

The _present resu]ts suggest that motion

integration

and segregation was

determined

based

on a

representation of metion

direction

modulated

by

thesurrounding motion.

Key words: visual motion. motion

integration,

illusion

The visual system uses two motion segmentation

mechanisms toextract object motion.

One

mecha-nism iscenter-surround interaction.Itiswell known

thata central stationary stimulus appears tomove in

the opposite

direction

of surrounding motion

{in-duced motion, Duncker, 1929). Another mechanism

is

motion segregation and integration in the same

visual

field.

When

two motion components are

pre-sented inthe same visual field,we will _perceive two

transparent motions when the

directional

difference

issufficiently large.Ifitisnot largeenough, we will

perceive one integrated,coherent motion

(van

Doorn

&

Koenderink,

I982),

The

visual system segregates

or integrates motion components depending on

di-rectional

differences.

In the present study, we examined the functional rclationship

between

these two _processes.

Experiment

1 Methods

The

participants were eight adults

(aged

19-25)

with normal or corrected-to-normal vision. The

stim-uli consisted of a central white random-dot

sur-rounded

by

a red randorn-dot display.

The

central

stimulus consisted of two _populations of random

*

_Department

_of

_Life

_Science$,

_The

_University

_of

Tokyo, 3-8-I Komaba, Meguro-ku, Tokyo

8902,

Japan

dots;

half

of the

dots

moved

leftward

while the

re-maining

half

moved rightward.

Under

the "Moving

Surround" condition, a vertically moving

random-dot

was _presented within a surrounding annulus,

Under

the "Baseline"

condition, half of _the dots

moved upward while the remaining

half

moved

downward. Each dot moved at 1.78deg/s inboth the

central and surround stimuli.

The

fixation

pointwas

located 4.5deg above the center. Both central and

surrounding stimuli were _presented

for

507

ms.

Par-ticipantswere then asked to

judge

how many motion

directionswere simultaneously _perceived inthe

cen-ter

(one

coherent or,two transparent motions),

After

the

_judgment,

they were asked to report the

per-6

40vov=

30.9g

2ob'

8

io.28o6a

Figure 1.

Results

of

Experiment

1,

Vertical

axis indicates the average of perceived

direction

of central stimulus where "O"

indicates purely horizontaL Error bars

represent ±

1 SEM.

,

The _JapanesePsychonomic _Society._Allrights reserved.

(2)

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

126 The

Japanese

Journal

of Psychonomic Science Vol.30, No. 1

ceived

direction

of the central stimulus through

di-rection matching.

Results

Participants

reported "`two

transparent motions"

in

most trialsunder

both

conditions. In Figure 1,we

plot

the

direction

matching results

in

trialswhere

participantsreported two transparent motions.

Un-der the "Baseline"

condition, _participantsfrequently

reported two

horizontal

directions,

which was

equivalent to the _physical directions. Under _the

"Moving

Surround"

condition, _participantsreported

two oblique directions,which was biasedtoward the

direction

opposite the surrounding motion.

These

results

indicate

that surrounding motion modulates

the

_perceived

directionof two central motions

simul-taneously.

Experiment

2 Methods

The stimulus and experimental _protocol were _the

same as

for

Experiment

1. We

_presented motion

components

in

two nearby

directions

{

± _15, ±_19,

±27, ±

45 deg

from vertical) in

the

center.

Central

stimulus speeds were different across directional

differenceconditions:

6.71,

5.15,

3,64,

and 2.3

deg/s,

respectively.

Three

surround stimulus condjtions

were

tested.

Under

the

"Baseline"

condition,

half

of

the

dots

moved upward while the other

half

moved

downward. Under the

"Same

Surround" condition,

all surrounding dots moved in

the

average direction of central motions, Under the "Opposite

Surround"

condition, all surrounding

dots

moved opposite the

central

direction.

The

surrounding stirnulus speed

was 1,78

deg/s

under allconditions.

Results

Figure

2 displays

data

on the

judgment

of motion

numbers

in

Experiment

2. Under

the "Same

Sur-reund" condition, _participants reported two

trans-parent

motions more frequently than under the

"Baseltne"

condition when central motion directions

were ±19,±27,and ±45 deg

to<.OOI,

two-tailed

Z

tesO.

Under

the

"Same

Surround"

condition, per-ceived

direction

was strongly

biased

toward the

di-

±rtse8

±rt9e.Ida.

±27:t8

±45o

O

O.2 O,4

O.6

O.8

1 Percentage

ef"two

motions"percept

Figure

2, Percentage of reporting "two

parent motions" in Experiment 2. Error bars

represent ±ISEM. Asterisks show

cant differences from data obtained under

the "Baseline" condition

{two-tailed

Z

test with

Bonferroni

correction: *,

p<O.OO1).

rection opposite the surrounding motion. The

re-ported

directions

(median:

±

80.5 deg

from

_the

verti-cal) deviated significantly from the _physical

direc-tion

_to<.OOI.

two-tailed Z tesO, In contrast, under

the "Opposite

Surround"

condition, participants

re-ported

one coherent motion more frequently than "Baseline"

under the ±

45 deg

condition

to<.OOI,

two-tailed

Z

test).In trialswhere participants

re-ported one coherent motion, perceived

direction

was

almost always ina purely vertical direction,

Discussion

Inthe _presentstudy we found that motion

integra-tion

and segregation were strongly modulated

by

surrounding motion,

These

results suggest that

rno-tion integration and segregation were

deterrnined

based

on the representation of motion directions

modulated

by

surrounding motion,

References

Duncker

L. (1950).

Uber

induzierte

Bewegung,

Ein

Beitrag zur Theorie optisch wahrgenommene

Bewegung, In W.D. Ellis

_(Ed.

& Trans.),Source

Book

of

Gestalt

Psychotogy.

Kegan

Paul,

Trench,

Trubner

&

Co,,

pp.

161-172.

(Original

work

pub-lished

in

(1929).)

van

Doorn,

A. _J.

&

Koenderink,

_J.

₍₁₉₈₂₎

Temporal

properties of the visual detectabilityof moving

spatial white noise. Emperimental Brain