Suppression of pattern detection in apparent motion trajectory(Summaries of Awarded Presentation at the 28th Annual Meeting)

The Japanese Psychonomic Society

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The JapanesePsychonomic Society

The1inPanese.tou･rnatofPkychonomicScience

201e,VoL 29,No.1,Sl-82

Summary

ofAwarded

Presentation6-114

Suppression

of

_{patterndetection}

inapparent

motion

trajectory

Souta

HiDAKA*'#,

Masayoshi

NAGAI**,

Allison

B.

SEKuLER***,

Patrick

_J.

BENNETT***,

and

Jiro

GyoBA*

7bhohu

University*,IVdtionalfnstitute

ofAdvanced

IndustrialScience

and

7]echnotogy:

(AJST}**,

and

McMaster

U)iiversily***

Letterdiscriminationisirnpairedwhen theletter

is

_presented within an apparent motion

(AecO

trajectoryof a spoL

This

finding

$uggests that the internalrepresentation of AM stimuli can

interferewith

_perception

at a relatively high _processing level.Here,we investigated whether AM

interferencealso occurs at an earlier processing

Ievel.

We

found

that the

detection

threshold of

patterns

defined

by

a

luminance

dimension

was

impaired

in

an

AM

trajectory. Further, this

suppressive effect of AM

became

weaker when the contrast _polarity,orientation, or shape of the

inducers of the AM and thetargetwas

inconsistent,

These

findings

suggest thatAM stimuli and

theirinternalrepresentation affect early visual processes involved indetectinga _pattern and that

the internalrepresentation of an

AM

stimulus reflects thestimulus's attribute.

Key

words: apparent motion, internalrepresentation, _pattern detection,contrast _polarity,

tien,

shape

ln

an apparent motion (AM) display,illusory

mo-tionperception vividly occurs even

in

a motion

tra-jectory

where no physical inputs exist. This

indi-cates thatthe representation ofan object undergoing AM can be established inthe whole trajectory,For

example, Yantisand Nakama

(1998)

found thatletter

discrimination was irnpaired when _the letter

fell

within the path of an AM trajectoryof a spot. This suggests that theinternaErepresentation of AIL,I

stim-uli ean interfcrewith our perception. However. ithas

remained unclear whether thisAM

interference

oc-curs only ina relatively high _processing stage

(letter

processing) or

in

a more

basic,

earlier _perceptual

proce$s Cpattern detection}. The current research

investigated

whether the

detection

performance of

Lhe_pattern definedinluminance

dimension

could be

impaired

inan AM trajectory.

General

Method

Stimuli.We presentedtwo inducers and one target

(a

square, 1×1deg,Figure 1)at

5

deg

below

a fixation

cross on a gray

background

(29,96

cd/m2). The hori-zonta] _gap between theinducers was 5 deg,and that

between

an

inducer

and the targetwas 2.5

deg.

The

*

_Deparment

_of

_Psychology,

_Graduate

_School

_of

Arts

and

Letters,

Tohoku University, 27-1,

Kawauchi, Aoba-ku, Sendai, 980-8576

#

_Current

_{arnliation: Deparment of Psychology,}

Rikkvo Universitv

On-AM-path

OfAM-path

FL

lnducer farget lnducer

Figure

1.

Schematics

of thestimuli and

tlons,

nme

ffme

lmecondi-inducers'

durations and interstimulusintervals

<ISIs)

were 106 ms, and the target's

duration

was 26 ms.

Procedure. In one condition, the target was

pre-sented

in-betwecn

the

inducers

COn-AM-path,

Figure

1),Ina second condition, thevertical _positionof the

inducers was displacedrelative tothetarget

by

2

deg

(Off-AM-path).

And, ina thirdcondition, two induc-ers simultaneousl;r flickeredso that an AM was not

perceived

(FL).

The

targetwas randomly _presented

once within 20 cycles of the AM sequences. Twe

series of 1 up,

-1

down staircases, were run for

estimating the 50% thrcshold. Whereas the Weber

contrast of thc inducers was constant

(100%),

the

target luminance varied along 32 tog-scaledsteps

from

±

2

te =100% of the Weber contrast. The

threshold was calculated

by

averaging the lastfour reversal data.

Three

conditions

(each

containing two Copyright2010.The

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82

The

Japanese

Journal

of

Psychonomic

Science

VoL

29,

No. 1

staircases presented

in

apseudo-random order) were

presented in a randorn order and counterbalanced

among theparticipants.

The

taskof the _participants

was toreport whethcr they perceived the targetor

did

not

(target

detection),

Table

1.

Contrast

thresholds

(Weber

contrast,

%)

obtained

in

Experiments

1,2,and

3,

On-AM-path

Off-AM-pathFL

Experiment

1:

Contrast

polarity

Exp.

IaExp.

IbExp,

lc

19.7-17.5-10.8

1L9-10.8

-8.5

13.9-10.9

-9.5

Whereas the contrast _polarityof both theinducers

and targetwas posjtive

(white)

in

Experiment

la,

it

was negative

(black)

inExperiment 1b, In Experi-ment 1c,the contrast of the

inducers

was positive,

and the contrast of the target was negative. Five observers participated ineach of theexperiments.

Results

and

Discussion.

In

experiments

la

and 1b

(Table

1),a one-way repeated ANOVA revealed a

significant main effect ofthe conditions (Experiment

la; F(2,8)=8.97,

_p<.01/

Experiment lb; F(2,8)=

13.02,P<.O1). A

_post

hoc

comparison

(Tukey's

HSD)

found that the contrast threshold intheOn-AM-path

condition became higher relative tothat inthe

Off-AM-path and FL conditions. The same tendency was

also found

in

Experiment lc

(F(2,

8)=7,90,

_P<,05).

However, the effect size

(d,

Cohen, 1988) in the

On-AM-path condition compared to the

Off-AM-path

and FL conditions, was weaker inExperiment 1c

<d

-O.69and O,81,respectiveLy) than thatinExperiment

la

(d=:2.08

and 2,29,respectively) and

Experiment

lb

(d==3.25

and 2.90,respectively}. These results

suggest thattherepresentation ofan object

undergo-ingAM can impair even early visual _processes,such

as

_pattern

detection.

Moreover,

this suppressive

effect can be modulated by the consistency of a

stimulus attribute Ccontrast)between the

inducers

and target, ConsistentInconsistent

Experiment

2:

Orientation

Exp. 2Exp,

3

25.316.9 18.612,8

IN'emanipulated the orientation of the stimuli

in

Experiment 2 in order to further investigate the

effect of the consistcncv of stimulus attribute on AM

intcrfcrence,We used Gabor _patches with vertical

stripes

(45

×45 _pixel

(1.5

deg),O.06cycle/pixel, o= 1O

pixel)as the stimulL

Whereas

the

inducers

and

targetwere tiltedat 45 deg intheConsistent

condi-tion,theorientation of thetargetwas

-45

deg

inthe

Inconsistentcondition. Only the

On-AM-path

situa-tionwas tested. Four observers participatedinthe experlment,

Results and Discussion. A two-tailedt-te$t

re-vealed thatthecontrast threshold inthe

_Consistent

condition was smaller than that inthe Inconsistent condition

(t(3}=

-2.35,P<.05,

d-2.93: Table

D.

This

indicates

that

AM

interference

was ]argerwhen the orientation of the target and inclucerswas consistent.

Experiment

3:

Shape

In Experiment 3,we tested the effect of shape

consistency on

AM

interference,Whereas the

induc-ers and targetwere square

(area:

1deg2)inthe

Con-sistent condition, theshape of the target was circular

{diameter:

1.12deg,area: O.96deg2)inthe Inconsis-tentcondition.

Only

the

On-AM-path

situation was tested. Sixobservers _participatedintheexperiment.

Results

and Discssion.

A

two-tailedi-testrevealed that the contrast threshold inthe Consistent condi-tionwas smaller than that

in

the

Inconsistent

condi-tion

(t{5)=2.97,P<.05,

d=2.74; Table 1}.This result

suggests thatthe AM interferencewas largerwhen

theshape of the targetand inducers was consistent.

General

Discussion

The present study showed that the detection of

patterns

defined

by

luminance was

impaired

when

the _patternwas _presented within an AM trajectory.

Moreover,

this suppressive effect of

AM

became

stronger when astimulus attribute

(contrast,

orienta-tien,or shape} of the target pattern was consistent

with thatof theobjects jnAM. These findings indi-cate that AM stimuli and their representation affect

early visual _processes

involved

in

detecting

a

pat-tem, and that the internalrepresentation of an AM

stimulus reflects _thestimulus's attribute,

References

Cohen,

J.

(1988).

Statistical

_Pozver

analJ,sis

for

the

behaviorat

sciences.

2nd

ed. New York:

Academic

Press.

Yantis,

S.

& Nakama,

T,

(1998).

Visual

interactions

in

the path of apparent motion. Nature Neu7oscience,