Hardness perception in visual motion : An experimental investigation in penetrating motion(Summaries of Awarded Presentation at the 28th Annual Meeting)

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

1'heJapaneseJoumalof Ps,1,chnnomicScience

2010,VoL29,Nu.1,77-78

Summary

ofAwarded

Presentation6-109

-AnHardness

perception

in

visual

motion

experimental

investigation

in

_penetrating

motion-TomohiroMAsuDA*,

Atsushi

KiMuRA*,

Ndtional

Food

Research

institute*,Sho-ichi

GoTo*2,

and

Yuji

WADA*

and

Uheiversity

of

71sukuba*2

We investigated the infiueneeof _{pre-penetration}and _penetration velocity changcs

(decelera-tionlconstant velocityfacceleration) on visual hardness

judgments.

Participants were asked to

judge,

using an analog scalc,

the

relative

hardness

of

the

penetrated objects compared to a

standard _pattcrn with no changes

in

acceleration,

The

results show that_perceptual hardness was

higher when the _penetrating object decelerated during _{pre-penetration,}or accelerated during

penetration,

but

was

Iower

when the velocity changed

from

acceleration todeceleration.

Our

findings

reveal that the visual perception of

hardness

is

infiuenced

by ve]ocity changes of the

penetratingobject

during

penetration.

In

addition.

the

current results

irnply

thatvc]ocity change

during

pre-penetration,which

is

not

directly

related toactual penetration in a natural environ-ment, isone factordetermining the visual perception of tcxture,

Key words: motion _perception,ex,ent _perception,non-rigid motion

The act of _piercing something iscalled

'"penetra-tion",

Motion

during

penetration varies depending

on the material of the objects involved and the

pene-tration

depth.

In

other words, changes

in

the

veloc-ity

of thepenetration provide rich cues for

determin-ingthe texturcof the penetrated object.

Some

researchers

have

reported thatwe _perceis,e

the various textures of objects based on visual

mo-tion.

For

exarnple, when an ebject moving with a

rapid change in ve]ocity crosses a border betw･een

different

colored

background

areas, observers

per-ceive a change

in

textureof the area that the object

passed

(Levelt,

1962), Thus we expcct thatthe

tcx-tureof a penetrated object can be _perceived from the

visual velocity changes during a _penetration evenL

Indeed,

a change

in

velocity

is

proportional tothe

forcesacting on theobject,

In the _present investigation we examined the

effects of velocity change of a _penetrating object on

theperceived texture of the

_penetrated

object, The

firstof two _phases was _{pre-penetration:}this ranged

from the approach of a _penetrating object to the

object whjch was _to

be

_{penetrated,to}when the

sur-*

_National

_Food

_Research

_Institute,

_2-1-12,

Kannondai, Tsukuba, Ibaraki

305-8642

**

_University

_{of Tsukuba, 1-1-1 Tennodai,}

Tsukuba,

Ibaraki

305-8573

e-mail:mastomo@affrc,go.jp

face

of thepenetrated object was touched.

The

sec-ond _phase was the _penetration of the object, Itcan

be assumed that: the velocity change in the

first

phase

implied

thestrength of _pressure forthe

pene-tration; and that the velocity change

in

the second

phase

implied

the

force

of

fricLion

acting on the

penetrating object.

Methods

Participants. Sixhealthy adults _participatedinthe

experiment

(average

age=30,33 years,

S.D.=5.68L

Thev al] had normal or corrected-to-normal vision,

Visual

patterns.

The

visual _patterns were pre-sented on a CRT monitor, In these_patterns,a

stick-like object

(penetrating

ebjecO approached and

pierced a

fixed

object

(penetrated

object, see Figure 1),

Wc rnanipulated the velocity changes

(deceleration,

constant velocity, acceleration} of _{thepenetrating}

ob-ject

in

two phases

(pre-penetration

and penetration),

which were

identical

in

duration

(1.0

sec) and were

presented sequentially without an intervaL Thus, a

total of nine visual _patterns with varied velocity

changes were generated,

The

patterns representing

each condition were _presented

in

random order.

Procedure. The head of each _participantwas fixed

toa chin-rest approximately

114cm

from

the

CRT

monitor and thc visual _pattcrns were observed

bin-ocularly in a dark room after a dark adaptation

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

78

The

Japanese

Journal

of

Psychonomic

Science

Vol.29,

No.

1

Table 1. Mean ratings of the surface and

internal

hardness.

Conditions

of velocity change Surface

hardness

Internal

hardness

Meant-valueMeant-value

Figure 1. An example of the visual _pattern

used

in

thisexperirnent.

dec-decdec-const

dec-accconst-dec

const-const const-acc acc-decacc-const acc-acc 5.85** 9.72** 4.37**

O.50

o.oo 5.59** O.97

2.3122.71

O.23O,31 o.ooo.oo

O.22O.04

2.352,473.212,34o.ooO.045.383.06O.25

{p<.05,*lp<.Ol

period of IOmin. Each visual stimulus was

pre-sented after the presentation of a standard _pattern

that

had

no velocity changes.

Participants

were

allowed to observe the stimuli as often as they

wished until they

felt

thatthey eould rate the

rela-tive hardness of the _penetrated objeet as compared

to that of the standard pattern,

They

judged

both

thesurface and

interior

hardness

of each penetrated

objecL When compared to the standard _pattern,the

perceived

hardness

was rated

by

using a visual

ana-logscale forhardness ranging from

"much

lower"to "much

higher",

Participants

were allowed tocheck

any point on the scale, Using a linearscale,

"much

higher" was assigned a value of 1and "much _lower"

was assigned a value of

-1,

with

O

indicating

thesame

hardness as the standard _pattern.

Results

and

Discussion

Table 1 displays the mean ratings of the surface

and

internal

hardness

as compared to the standard

pattern,and the results ofthe two-tailedt-tests.

The

abbreviations

indicate

the conditions of velocity

change for _{pre-penetration} and _penetration

(e,g,,

"acc-const" _indicates

acceleration during the

pre-penetration phase and constant velocity

during

the

penetrationphase).

These results indicatethat the surface hardness

was significantly higher than zero under all

pre-penetration

deceleration

conditions and all

penetra-tionacceleration conditions,

The

internal

hardness

was significantly higher than zero under thedec-acc

and the acc-const conditions, and lower than zero under theacc-dec condition.

The results reveal that thesurface of thepenetrated object was _perceived as

harder

when the penetrating

object decelerated during pre-penetration or

acceler-ated duringpenetration. The insideof the _penetrated

object was

judged

as

]ess

hard

when the penetrating

object went from acceleration todeceleration,

Generally,

the motion of penetration

into

a

hard

surface issaliently slowed by the elastic deformation

of thepenetratedsurface _priorto

fracture,

after which

the penetratingobject beginstoaccelerate as it

perfo-rates the _penetrated object. On the other hand the

deceleration

of the penetrating object,

due

tosurface

elastic deformation, isslight when the _penetrated

ob-ject

has

a soft surface.

Taken

together,the current

results suggest thatthe visual _perceptionof the

tex-tureof a _penetratedobject isachieved using

naturally-occurring motion cues such as velocity change. In

addition, the current results imply that

pre-penetration velocity change, which

is

not

directly

re-latedtoactual _penetrationinanatural environment, is

one determining factorinvisual texture _perception.

References

Levelt,

W.

J.

M,

<1962).

Motion

braking

and the

tionof causality, In

Causalite,

Permanence

et reatite

Phenomenates

rPhenomenal

causatity,

Permanence

and realitMl Louvain: PublicationsUniversitairesde