Relationship between the Rotating Snakes illusion and the temporal impulse response function in the visual system(Summary of Awarded Presentation at the 26th Annual Meeting)

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

V'heJaPaneseYournatofIlsycho･nomieSeien(/e

2008,VoL 27,No. 1,107-le8

Summary

ofAwarded

PresentationIP25

Relationship

between

the

Rotating

Snakes

illusion

and

the

temporal

impulse

response

function

in

the

visual

system

Rumi

HIsAKATA

and

Ikuya

MuRAKAMi

UniversiC),

of

lbhNo'

The Rotating Snakes i]lusionisa motion illusioninwhich a static figureappears to rotate.

Murakami

et al.

(2006)

proposed the model that the biphasic shape of the temporal impulse

response

(TIR>

function

induces

this

illusion,

We

attempted totestthis

hypothesis

by

manipulat-ingretinal illuminance because itiswell known that the shape of the

TIR

function changes from

biphasictomonophasic with decreasing retinal il]uminance. The resu]ts indicatedthatthe

illusion

strength indeed

decreased

with

decreasing

retinal

illuminance.

To

obtain a

better

view of the

change

in

temporal response _property, the TIR functions were estimated by

the

double-pulse method

_(Burr

&

Morrone,

1993) under certain lightconditions. We confirmed that the biphasic

character of TIR gradually changecl tomonophasic with

decreasing

retinal

illuminance.

We

argue

that the

_biphasic

characteristic of the TIR function contributes tothe illusionstrength.

Key words: i]lusion,temporal

impulse

response, visual motion perception

The

Rotating

Snakes

illusien

i$

one of the most compelling illusionsinwhich a static

figure

appears

to move

{Kitaoka

&

Ashida, 2003). This illusionis

composed of regularly repeated,

4-step

luminance

patterns of black,dark _gray, white and lightgray,

The patterns are repetitive

in

a circular fashion,and

the illusorymotien isperceived

in

the

direction

cor-responding to the order of the abovementioned lumi-nances. Murakami, Kitaoka, & Ashida

(2e06)

showed a positive cerrelation

between

the strength of

the

Rotating

Snakes

illusion

and the amplitude of

fix-ational eye movements. They suggested that the

biphasic

shape of the temporal

impulse

response

(TIR)

function

in

the visual system causes this

illu-sion. The objective of the present study was to test

their

hypothesis.

In

generaL

it

is

known

that the

shape of the TIR function changes with retinal

illu-rninance] the

biphasic

shape

becomes

monophasic

with decreasing retinal illuminance

(Burr

& Morrone,

1993;

Swanson,

Ueno,

Smith,

&

Pokorny,

1987).

On

the basis of these facts,we examined whether the

strength of the illusionchanges with retinal

illumj-nance, Ifthe

hypothesis

by

Murakarni

etal.

(2006)

is

correct, the Retating

Snakes

illusion

may disappear

*

_Department

_of

_Life

_Sciences,

_{The University of}

Tokyo,

3-8-1

Komaba,

Meguro-ku, Tokyo

153-8904

when the retinal Muminance decreases because the

biphasic

shape of the

TIR

function

should disappear,

Inthe

first

experiment, we examined thestrength of

the illusionat various retinal illuminances, Inthe second experiment, the

TIR

functions

under various retinal il]uminances were measured.

Experiment

1

Methods

The subjects were one of _the authors and

3

naive adults with norma] vision. The stimulus was a ring

that comprised 24 cycles of _the abovementioned

lu-minance _patterns.

The

outer and

inner

diameters

of

the ring were 7deg and 1deg, respectively. We set

up 2 versions of the stimuli such that the expected

direction

of

illusory

motion was clockwise

{CW)

and

counter-clockwise

(CW).

The

stimulus was

_presented

on a

CRT

monitor

(75

Hz,

O.025

deglpixel)

for

500

ms

intheleftvisual hernificld,The subject used only the right eye and made atwo-alternative

forced

response as to which direction,clockwise or counter-clock-wise, thestimulus ring appeared terotate.

We

quantified the

illusion

strength as the

cancella-tion velocity that

just

nulled the

illusory

motion.

The stimulus was physically rotated at various

ve-locities,and the _pointef subjective stationarity was estimated foreach of the CW and CCW stimuli by the

The Japanese Psychonomic Society

NII-Electronic Library Service

The JapanesePsychonomic Society

108

The

Japanese

Journal

of

Psychonomic

Science

Vol.

rnethod of constant stimuli, To manipulate retinal

illuminance. neutral-density

filters

were used.

A

fiI-terhaving ene ef the 6 transmittances

(16

]-512 i) was _placed

in

front

of the subjects' right eye. The

pupildiameter of each subject was measurecl ateach

filter

condition and the retinal

illuminance

was cal-culated as the delivered luminance divided by _pupil area.

Results

The illusienstrength against retinal illuminance was _plotted foralt subjects as shown

in

Figure

1(a).

The

linear

regression analysis across subjects was significant

(t=6.97,p<O.OOI).

Insummary, we found that the illusionstrength decreases with

decreasing

retinal

illuminance.

The

widely accepted view

is

that the decrease inretinal illuminance corresponds to the change inthe TIR function frornbi-to

mono-phasic

(Burr

&

Morrone,

1993;

Swanson

etal.,

1987).

Our results are consistent with those of Murakami et ai,

(2006),

which state that

the

biphasic

shape of the

TIR

function

is

involved

in

the visual _processing

underlying the Rotating

Snakes

illusion,

Experiment

2

Methods

To measure the actual TIR, the double-pulse

method

{Burr

&

Morrone,

1993)

was used.

The

Gabor

patch

(a=l.75

deg,

1

cfdeg) was presented at 12deg eccentricity in the lefthemifield for1 video frame.

After

the

first

patch,the second _patch was _presented at the same position after a certain stimulus-onset

asynchrony

{SOA).

The 2 _patches had the same

polarity

in

one session and opposite _polaritie$

in

the

other;

31

SOAs

{16-296

ms) were used

for

all

ses-sions. The 2-intervalforced chotce was used; one

intervalcentained the stimulus

(2

successive Gabor

patches as

described

above) and the other

interval

contained no stimulus, and the subject identifiedat which intervalthe stimulus appeared. The contrasts of

2

successive patches were changed, and the con-trast threshold was measured under each SOA condi-tion. Frorn the contrast sensitivity _profiles,the TIR

function

was estimated with the rnodel

by

Burr

and

Morrone under 3 retinal illuminance conditions.

27,

No.

1

(a)

fo)

2 tpO･3

:t

1

lo2

Z

:/

o,i

S.O

U2

-1

8D

O 1 2 3O o.2 O.4 Rttinalillum;nancc(]ogtd) Tlme(sec)

Figure 1.

(a)

Illusion strcngth against retina]

illuminance.

(b)

TIR functions at 3 retinal i]luminances.

Results

Figure 1{b)shows the estimated

TIR

functions.

The

shape of the

TIR

function,

in

fact,

changed

from

bitomonophasic with decreasing retinal illuminance.

The

biphasic

shape of the

TIR

function

is

known

to

be a very important signature

for

transientmotion processing. Thus

it

is

probab]e that the transient

processing contributes to the illusion.

Discussion

We found that theillusionstrength decreased and

the

shape of

the

TIR

function

changed with retinal

illuminance,

The biphasic characteristic of theTIR

indicates

the transient temporal-frequency

process-ing in the visual system.

From

_these results, we

suggest thatthe transientmotion processing contrib-utes to the Rotating Snakes illusion.The _present results are consistent with those of Murakami et al,

(2006).

References

Burr,D.C.,& Morrone, M

C.

(1993>.

Impulse-response

function

for

chromatic and achromatic stimuli.

.JOunial

of

the

0Pticat

Society

of

America A, 10,

1706-1713.

Kitaoka,

A.,

&

Ashida, H.

(2003).

Phenomenal

charac-teristics

of

the

_peripheral

drift

illusion.

VISION,

15,

261-262.

Murakami, I.Kitaoka, A.,& Ashida, H.

(2006).

A

positive correlatien between fixation instability

and the strength of

illusory

motion

in

a static

display. VisionRes,,46,2421-2431.

Swanson,

W.

H.,

Ueno,

T.,

Smith,

V.

C.,

&

Pokorny.

J.

(1987).

Temporal

modulation sensitivity and

pulse-detection thresholds forchromatic and luminance perturbations.

f

Clpt,Soc.Am. A,4,1992-2005.