1-B-22 潜在記憶は時間知覚を短縮させる(2002年度 日本基礎心理学会第21回大会優秀発表賞)

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

77ielbPaneselbumatofPsychonomtcScience

2003, VoL 22,No,1,29-30

Prizewinner's

Summary1-B-22

The

effect

of

_previously

subthreshold

exposures

on

the

perception

of

a

_period

of

time

Fuminori

ONo,

Daisuke

FuJiKi,

and

Jun-ichiro

KAwAHARA

Hiroshima Uitiversity*

The perceived

duration

of events

is

known

to

be

affected

by

factors

thatare at

least

partly

conscious,

In

the present study we report that the perceived

duration

of visual events can

be

affected even by an uncenscious factor. The

_participants

were briefly

(12.5rns)

exposed to nonsense syllablcs which were followed by backward _patternmasking. A discrimination test for

other _participants confirmed that the stimuli were _presented

below

a threshold

level,

The

participants subsequently estimated the duration of the _presentation oi each of the nonsense syllables thateither had,or had not, been _previouslyexposed, The results indicatcdthatthemean estimated duration of the stimuli that were _previously exposed was lessthnn that forthe new

stimuli.

These

results suggest thatunconscious experience

is

one of

determinants

that

can reduce

theperceived

duration

of events,

Key words: time _perception,subthreshold exposure

It

has

been

shown that the perceived

duration

of events can

be

increased

or decreased by several

fac-torswhich Matsuda

(1996}

has classified intothree categories.

The

first

is

cognition of the non-temporal

attributes of event$: theperceived duration increases

when we recognize the stimuli as more numerous,

intensive,complex andfor

large.

The

second

is

the

level

of attention to the passing of time:the

per-ceived

duration

increases

when we attend more to

the tirnewhich has elapsed. Thc third is

neuro-physio]ogicalexcitement: the _perceived duration

in-creases when we are mere excited

neurophysiologi-cally.

Most of the _previous studies which have

investi-gated

the

determinants

modulating _{theperception} of

thetime of

brief

events

have

considered

factors

that

were censciously sensible,

for

example, cognition of

the non-temporal attributes of events, and the level

of attention

to

the elapsed

time,

In

other words,

previous studies

have

examined

factors

that are at

least

_partly

conscious. Thcre is,however, an

unan-swered _questioniisthe _perceived time span affected

by completely unconscious

factors?

Specifically,

when estimating thc

duratien

of avisual event, can a

* _{Department of Psychology, Hiroshima}

sity, Kagamiyama 1-1-1, Higashi-Hiroshima

739-8524

earlier subthrcshold experience of the same event

vary the perceived duration of it? To our

knowl-edge, the effect of an unconscious experience on time

perception

has

not

bcen

studicd.

We

therefore

con-ducted the present study toclarify whether or not

unconscious experience could have effects on time

perception.

The

experiment consisted of two phases,

In

the

exposure _phase, the _participants viewed

brief

dis-plays of nonsense syllables with backward masking

so thatthey could not see what was _presented. Inthe

time perceptionphase, the participants estimated the

duration for which a sy]lable was displayed, for

either a _{previously presented} syllable or fora new

syllable,

If

the perceived

duration

was affected

by

the subthreshold exposures, then we

be]ievcd

that

therewould bedifferences

in

theestimated durations

of the displays ef the new and the _previous]y

pre-sented syllables,

Method

Participants Twelve naive students _participated

in

the main experimental sessions and ten

partici-pated

in

the

discrimination

task.

Stimulusmaterials The stimuli were 50

non-sense syllables each consisting of two

Japanese

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30 The

_Japanese

_Journal

of Psychonomic

Science

VoL

22,No.

1

as white on the grey

background

of a cemputer screen,

Proeedure

Exposure phase

Fifteen

randomly chosen

sylla-b]es

were assigned toeach of threeconditions: the

O-exposure, the 1-exposure,and

the

10-exposure

condi-tion,During the exposure _phase,

15

items

from

the

10-exposure condition were presented

le

tirnesand

15

items

from

the 1-exposure eondition were

pre-sented once, in a random order, resulting in 165

exposures. The _{participantspressed the}space

bar

of

the computer

keyboard

to

begin

a scquence.

After

the

display

of a

fixation

dot

for

2seconds, a syllable

was _presented in

the

centre o[

the

monitor scrccn

for

12.5ms, and this was immediately followed

by

the

display

of a pattern mask

for

100 ms. The

partici-pants were

instructed

topay close attcntion te thc

fiashing_patternson the screen.

Time

perception phase

Aftertheexposurephase,

the participantswere instructed tomake

cornpara-tive

_judgments

of the duration of the standard and

comparison stimuli,

When

the

participantspressed the space

bar

to

begin

each trial,a

fixation

dot was

first

_presented

for

1

second, then a square

fi11ed

with random dots followed for 300 ms, as the standard stimulus, After a

blank

of

1

second, a syllable

ap-peared

for

ejther

1OO,

200,

300,

400,

or

500

ms, as the

cornparison stimulus. The ratio of the duration of

the

display

was

balanced

over all conditions.

The

participants were _{given three} sheets of paper on

which 20horizontallineswere

_printed.

The

partici-pants wcre toldtomark anywhere on a lineto

indi-cate _theduration of thecomparison stimulus relative

to the standard, the

duration

of which was

repre-sented as one

half

the

length

of a

line.

Diseriminationtask This task was to confirm

that

thc

prcsentatiensofthe stimuli

in

theexposure

phase were subthreshold. The 50 nonsense syllables

and 50

b]anks

were each displayed

for

12.5ms inan unpredictable order, Each exposure was _preceded

by

a 2second fixation_period and followed

by

apattern

mask ef 100 ms. The _participantsreported whether

the syllables were presented or not,

Table 1

The

mean estimated duration

(in

ms) as a

function

of the exposure frequency in the exposure _phase.

Exposure

frequency

o 1 10 Estimated

duration

SD

228,OO

224.57

218.57

(26,12)

(31,08)

(28.09)

Results

and

Discussjon

The mean of the estimatecl

duration

under each condition

is

presented

in

Table

1.

An

analysis of variance, with the exposure

frequency

as a within-subject variable, was used to statistically exarnine

the

data,

The

analysis revealed a significant main effect of cxposure

frequency,

F(2,22)=3.75,

p<.05.

Multiplccomparisons

(Ryan's

method) indicatedthat

the mean estimated duration of _the 1O-exposure

con-dition

was significantly

less

than that of the

O-exposure condition, t(22}=2.74,P<,05,

The

result

indicated that the _perceived duration was affected

by repetitive _{presentation.} Specifically,repetitive

exposures ofthe visua] stimuli reduced theperceived

duration of thc stimuli.

The mean number of correct identifications

in

the

discrimination

taskacross allof theparticipantswas

51.3

(of

100

measurements,

SE=3,23),

Overa]L

the

participants correct]y identified513 of 1,OOO expo-sures, a result which does not differsignificantly

from

chance,x2(1,N=

1,OOO)=O,67,

The

results of the

discrimination

task confirmed that the presentation ofthe syllables inthe exposure _phase was subthresh-old.

In

all,our results are the

first

toreport the effect

thata previous subthreshold experience can reduce

the_perceived duration of an event. This study

there-foreadds unconsciousness factors_tothelistof

deter-rninants which can affect time perception,

References

Matsuda, F,1996 Time estimation,

In

F,

Matsuda,

K.

Choshi,

K.

Komura,

H.

Jingu,

K.Yamasaki, & S,

Hira

(Eds.),

Psychotogical

tinze:a

broad

and

deeP

myste,:y. Kyoto: Kitaoji-shobou.Pp.87-144

(In