2P069 立体刺激の形状が大きさ知覚に及ぼす影響(2003年度 日本基礎心理学会第22回大会優秀発表賞)

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The JapanesePsychonomic Society

1'heJopan'eseJoumaiofIlsychonomicSeience

2V04,VoL23,N[},1,111-]12

Summary

ofAwarded

Presentation2P069

The

efTect

of

3-Dshape

Shuichiro

TAyA

KIv,ushu

on

size

_perception

and

Kayo

Unit:ersily*MIuRA

Recent studies $uggest thattheshape of three-dimensiona]

(3-D)

objects causes thesystematic

distortionof theirapparent size

(Miura

& Taya, 2001) and we have invcstigatedwhich _property of

the objects may do this.The stirnuli were stereograms

defining

four

3-D

shapes: a _pair of

frontoparallc]rectangles, a triangular ridge, a cylindrical ridge, and a trapezoidal ridgc. Thc

observcr's task was tomatch the

height

of a

Eine-drawing

of a rectangle

(comparison

stimulus) to thatof thestimuli, The results showed

that

the

apparent

height

of

the

object

decreasecl

as thcslant

of theirsttrface _protruding from the

background

was

increased.

The results impliedthatour visual

svstern takes account of theslant of a surface forsize estimation. Key words: size _perception,surface slanL

3-D

shapc

Prcvious studies have reported that observers

made systematic errors when they estimated size

and

depth

in

a

3-D

space

{Norman,

Todd, Perotti,& Tittle,1996).Most of these studies have attributed

tbe

errors toan

incorrect

estimation of theviewing

distance,However, recently we demonstrated that

the apparent width of cylindrical objects dccrcased as

their

depth

increased,

indicating

_{that the}

3-D

shape causes a systematic error

in

sizc cstimation

(Miura

&

Taya, 200D.

The goal of the _present study was toidcntifythe

factorcausing the systematic

decrernent

of the

ap-parent size of

3-D

objects, Whenever thc depth of a cylinder changes itsother 3.D _properties

(slant

and curvature) also change.

Therefore,

it

has

not

been

clear which property critically affects size

percep-tion.In Experiment 1,we examined whether the

depth itselfaffccts apparent size,

We

mea$ured the

apparent height of different]yshaped 3-D objeets.

The simulated depths of the objects were

equiva-lentlyset across all shapes,

Therefore,

if

the

depth

itselfwas the factorof the systematic error of size

perception, the apparent heightof theobject wou]d

be dependent on itsdepth but independent of its

shape.

* _{Department of}

_Psychology,

_Graduate

_School

of

Human-Environment Studies, Kyushu

sity,

6-19--21

Hakozaki,

Higashi-ku,

Fukuoka 812-8581

Experiment

1

Method Eight observers _{participated.}The _test

stimuli were random-dot stereograms

depicting

one

of three

3-D

shaped objects: a _pairof

frontoparallel

rectangles, a triangularridge, and a cylindrical ridge

(Figure

1(a}-(c)),The te$t$timuli had thesarne

hori-zontal width

<5cm)

but

either of two

different

hei-ghts

(4

or 5crn). The simulated depth was 2,4,and 6

cm at

the

viewing

distance

of

60

cm.

A

tine-drawing

of arectangle was presented

below

theteststirnulus.

An observer's task was to match the height of a

rectangle to that of a test stimulus. To obtain the

baseline

for

normalization a single randomdot

rec-tangle of the same width and

height

as the test

stimuli was _presented inanothcr scssion. The observ-ers again used thesame _procedure inanother eight

trialsof the

heighVmatching

task

for

thisrectangle.

Results and Discussion Figure 1(e)shows how

the

apparent

height

varied as a function of

depth

fer

each of the three shapes.

To

normalize the

large

indi'vidual

difference,the matched

height

for

each

stimulus isrepresented as the ratio against the

base-line

value. An analysi$ of variance revealed thatthe

matched

height

of the cylinders

decreased

as their

depth increased

(FC2,7)

=27.3,

P<

,OOI).

A _similar

dec-rement of matched height was also observed with

the

deepest

(Le.

depth=6

cm) triangularridge.

How-ever, the rnatched heights of the rectangular

_pairs

The Japanese Psychonomic Society

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112

The

_Japanese

_Journal

of

PsychonomlcScience

VoL

23,

No.

1

(a)

r

-'

T

l

(c)

-".-/--l/t1,

'tXx

L-.-(b)

4

-(

-7

x.,.--->s

Vwodtr1 , HeigM

(dl.-r"--(Jlel

Depth SkuTt

ri.05(e) errerbars=s,e.m. 1.ooo

enrorbars=s.e,m,

2zz8esu.gaenrepp9EoLt8stsE

t.oo O.95 e.go t

to

Zde e2 4 6 Simulateddepth_(cm) O.98 O,96 O.94 O.92

-t-T

Figure 1.

_(a)-(d)

Schematic diagrams of thestimuli used

in

thisexperiment. The d

"slant"

is

indicated by the arcs fi11edwith gray.

(e)

The results of

Experiment

2.

See

text

for

more

details,

O.90S

7e 75 80 85

Simulatedslant(degree)

efinition of the word

Experiment

1.

(D

The

results of

ge

The results suggest that some properties of 3-D shape other than

depth

(e,g,

slant or curvature)

af-fectedthe apparent height.In thisexperirnent, the

depth of the objects was equivalent across allof the

shapes,

However,

the

decrement

of height was only observed

in

cylindrical ridges and the deepest

trian-gular ridge. Depth therefore,isnot the main

factor

causing thedecrement of the apparent height.

We

presurned thattheslant of asurface protruding

from the background affects the apparent

height

(For

the definitionof "slant",

see Figure 1).The slant

of tbe cylinder was much steeper

than

that

of the

triangularridge or the _pairof rectangles even ifthe

depth of the objects was equivalent. Consequently,

we

hypothesized

that

a steeply slanted surface

caus-es a decrement of theapparent

height,

Wc

examined

this

hypothesis inExperiment

2,

Experiment

2

Method Five observers participated,

The

test

sti-muli were random-dot stereograms defininga

trape-zoidal ridge

(Figure

1(d)).

The

depth-to-height

ratio of the ridge was 1:1. The

heights

(and

simulated

depths) used were 4 and 5cm. The horizontalwidth

of theteststimu]i was always 5cm. The simulated slant of the surface against the

frontopara!lel

back-ground was selected

from

74,

76.

80,

84,

and

87

degrees,

The

observers _participatedin eight blocks

of

10

trials.Allother experirnental conditions were

the same as Experirnent 1.

Results and Discussion Figure 1(f)illustrates

how the apparent

height

varied as a function of the

surface slant, An analysis of variance showed that

thepercejved heights of the 3-Dstirnuli decreased as

theirsurface

became

steeper

{F(4,4)

:='

9.98,

P<.OO1).

The results supported our hypothesis that the slant of the surface of the 3-D objects caused a decre-ment

in

thc apparent

height

of

them,

Probably

the

reason why only cylinders and the

deepest

triangu-lar

ridge showed a heightdecrement

in

Experiment

1

was

because

the slant of theirsurface was much steeper than that of other stimuli.

The

results sug-gesttherefore, thata slanted surface affects the

per-ception of size,and especially when the slant has a certain steepness,

The

results suggest

that

the

visual

system may take account of the surface slant when

size isestimated. This isLikelybecause thesize isthe extent of the orthogonally _projectcdimage of a

sur-face,and thiscan be varied

depending

on the surface

slant.

References

Miura, K. & Taya, S.2001 New size

illusion-Docs

theincreaseof _perceived depth leadto the

decrease

of _perceived width?

PercePtion,

30(supplement):

22

-23.Norman,

J,

F.

Todd,

J,

T.

PerottL

V.

J.

&

Tittle,

J.

S.

1996 The visual perception of three-dimensional

length.

fournal

of

Emperimentat

Rsychology:

Hbeman

RircePtion

and Peijbrmance, 22:173-186,