Variations

in

-LRB-

MIBG

-RRB-

late

heart

mediastinal

ratios

in

chronic

heart

failure

a

need

for

standardisation

and

validation

Background

There

is

lack

of

validation

and

standardisation

of

acquisition

parameters

for

myocardial

-LRB-

MIBG

-RRB-

This

lack

of

standardisation

hampers

large

scale

implementation

of

parameters

in

the

evaluation

of

patients

with

chronic

heart

failure

-LRB-

CHF

-RRB-

Introduction

Radiolabelled

metaiodobenzylguanidine

-LRB-

-RRB-

an

analog

of

the

false

neurotransmitter

guanethidine

localises

in

adrenergic

nerve

terminals

primarily

via

the

norepinephrine

-LRB-

NE

-RRB-

transporter

-LRB-

-RRB-

system

-LSB-

-RSB-

In

the

past

two

decades

a

large

number

of

investigators

have

demonstrated

decreased

myocardial

uptake

in

heart

failure

patients

and

have

shown

that

those

with

the

lowest

uptake

tend

to

have

the

poorest

prognosis

-LSB-

-RSB-

There

have

also

been

findings

suggesting

that

abnormalities

of

myocardial

uptake

may

be

predictive

of

increased

risk

for

ventricular

arrhythmia

and

sudden

cardiac

death

-LRB-

SCD

-RRB-

-LSB-

-RSB-

One

factor

that

has

constrained

acceptance

of

cardiac

imaging

as

a

clinical

patient

management

tool

in

heart

failure

has

been

the

variability

of

technical

aspects

of

the

procedure

Although

most

publications

have

included

the

heart-to-mediastinum

ratio

-LRB-

H/M

-RRB-

as

the

measure

of

myocardial

uptake

the

methods

used

to

obtain

this

parameter

show

considerable

variation

In

addition

the

influence

of

procedural

and

acquisition

parameters

on

the

reproducibility

of

this

measurement

technique

have

only

occasionally

been

considered

While

the

effect

of

collimator

selection

on

H/M

ratios

has

been

studied

similar

attention

has

not

been

paid

to

the

impact

of

administered

activity

acquisition

time

and

duration

-LSB-

-RSB-

Given

the

absence

of

published

guidelines

for

cardiac

imaging

standardisation

of

procedures

among

individual

users

of

this

agent

becomes

even

more

important

The

objective

of

the

present

study

was

to

examine

the

influence

of

procedural

variables

associated

with

imaging

when

a

standardised

technique

was

used

to

determine

the

H/M

ratio

Materials

and

methods

Study

design

Myocardial

scintigrams

on

heart

failure

patients

-LRB-

male

and

female

subjects

years

of

age

with

New

York

Heart

Association

-LSB-

NYHA

-RSB-

Classes

II

IV

-RRB-

from

six

sites

in

five

European

countries

were

retrieved

and

analysed

These

imaging

studies

were

performed

between

and

and

were

collected

for

a

previously

described

trial

-LSB-

-RSB-

This

trial

was

designed

to

show

that

standardised

methodology

could

be

applied

to

the

analysis

and

processing

of

myocardial

images

to

obtain

reproducible

quantitative

results

As

the

large

majority

of

patients

had

only

late

planar

images

the

analysis

of

these

images

is

the

sole

focus

of

this

paper

Investigational

sites

sent

copies

of

all

digital

image

files

to

an

Imaging

Core

Laboratory

-LRB-

ICL

-RRB-

for

evaluation

and

analysis

Data

on

amount

of

activity

injected

and

image

acquisition

parameters

-LRB-

i.e.

delay

after

injection

of

and

start

of

acquisition

acquisition

duration

and

type

of

collimator

used

-RRB-

were

collected

The

primary

efficacy

objective

of

the

original

trial

was

to

determine

the

prognostic

significance

of

the

late

H/M

ratio

in

relation

to

occurrence

of

major

cardiac

events

-LRB-

MCE

-RRB-

defined

as

either

-RRB-

cardiac

death

due

to

all

causes

including

myocardial

infarction

-LRB-

MI

-RRB-

progressive

heart

failure

and

sudden

cardiac

death

-LRB-

SCD

-RRB-

-RRB-

cardiac

transplant

-RRB-

potentially

fatal

arrhythmic

event

including

resuscitated

cardiac

arrest

or

appropriate

internal

cardiac

defibrillator

-LRB-

ICD

-RRB-

discharge

Results

of

that

analysis

have

been

published

For

the

purposes

of

this

paper

H/M

thresholds

associated

with

low

intermediate

and

high-risk

for

MCEs

were

defined

to

provide

the

basis

for

the

multivariate

analysis

described

below

Image

analysis

An

experienced

nuclear

medicine

technologist

not

affiliated

with

the

ICL

processed

all

the

planar

images

to

determine

the

heart/mediastinum

-LRB-

H/M

-RRB-

ratio

The

heart

region

of

interest

-LRB-

ROI

-RRB-

was

drawn

manually

to

include

both

ventricles

and

any

atrial

activity

that

was

clearly

visible

A

square

mediastinal

ROI

was

drawn

in

the

upper

mediastium

using

the

apices

of

the

lungs

as

anatomic

landmarks

-LRB-

Fig.

-RRB-

The

H/M

ratio

was

calculated

as

the

ratio

of

the

counts/pixel

in

the

two

ROIs

Fig.

of

processing

procedure

for

late

planar

images

The

positioning

of

the

mediastinal

ROI

was

standardized

in

relation

to

the

lung

apex

the

lower

boundary

of

the

upper

mediastinum

and

the

midline

between

the

lungs

Statistical

analysis

Data

are

presented

as

mean

standard

deviation

unless

indicated

otherwise

Kaplan

Meier

survival

analysis

and

the

log-rank

test

were

used

to

analyse

differences

in

event

rate

for

different

subject

groups

defined

by

the

late

H/M

thresholds

Differences

between

these

groups

for

continuous

data

were

compared

using

analysis

of

variance

-LRB-

ANOVA

-RRB-

with

a

post

hoc

Bonferroni

Categorical

data

were

compared

using

the

Fisher

's

exact

test

A

forward

stepwise

multivariate

regression

analysis

was

performed

to

determine

independent

predictors

of

late

H/M

Explanatory

variables

were

related

to

patient

characteristics

-LRB-

i.e.

gender

age

NYHA

class

left

ventricular

ejection

fraction

-LSB-

LVEF

-RSB-

and

underlying

etiology

of

heart

failure

-RRB-

and

to

acquisition

parameters

-LRB-

i.e.

amount

of

injected

activity

collimator

type

delay

after

injection

and

start

of

acquisition

and

duration

of

acquisition

-RRB-

Multivariate

forward

stepwise

regression

analysis

was

performed

for

all

study

subjects

The

overall

goodness-of-fit

for

each

model

was

expressed

as

the

adjusted

The

F

test

was

used

to

assess

whether

a

model

explained

a

significant

proportion

of

the

variability

A

p

was

considered

to

indicate

a

statistically

significant

difference

All

statistical

analyses

were

performed

with

SPSS

-LRB-

SPSS

for

Windows

version

SPSS

Inc

Chicago

IL

USA

-RRB-

Results

As

previously

described

there

were

major

cardiac

events

Figure

shows

a

Kaplan

Meier

survival

analysis

for

three

different

groups

of

late

H/M

Quantitative

estimates

for

low

risk

-LRB-

late

H/M

survival

of

-RRB-

intermediate

risk

-LRB-

late

H/M

survival

of

-RRB-

and

high

risk

-LRB-

late

H/M

survival

of

-RRB-

could

be

determined

The

differences

in

event

rate

were

statistically

significant

between

the

three

groups

-LRB-

all

p

-RRB-

Fig.

Meier

curve

showing

the

relation

between

survival

and

time

to

first

major

cardiac

event

for

three

groups

with

different

H/M

values

late

H/M

vs

late

H/M

p

late

H/M

vs

late

H/M

p

late

H/M

vs

late

H/M

p

Table

shows

the

baseline

characteristics

and

the

parameters

related

to

the

acquisition

of

all

subjects

and

for

the

three

different

groups

of

late

H/M

Overall

the

majority

of

subjects

were

male

and

were

in

functional

class

II

according

the

NYHA

classification

and

had

a

LVEF

-LRB-

n

-RRB-

Between

the

three

late

H/M

groups

there

were

differences

in

age

-LRB-

subjects

with

a

late

H/M

were

younger

-RRB-

NYHA

classification

LVEF

-LRB-

increasing

from

subjects

with

a

late

H/M

to

subjects

with

a

late

H/M

-RRB-

and

HF

etiology

In

addition

there

were

no

differences

in

parameters

of

heart

failure

-LRB-

LVEF

and

NYHA

classification

-RRB-

between

the

different

centres

Table

and

scintigraphic

parameters

for

all

subjects

and

subdivided

by

late

H/M

All

-LRB-

N

-RRB-

Late

H/M

-LRB-

N

-RRB-

-LRB-

N

-RRB-

-LRB-

N

-RRB-

Patient

characteristics

Age

-LRB-

years

-RRB-

-LRB-

-RRB-

NYHA

-LRB-

II/III/IV

-RRB-

LVEF

-LRB-

-RRB-

-LRB-

-RRB-

Etiology

of

heart

failure

-LRB-

isch/non-isch

-RRB-

Scintigraphic

parameters

Collimator

type

-LRB-

LEGP/LEHR/ME

-RRB-

Activity

-LRB-

MBq

-RRB-

-LRB-

-RRB-

Delay

after

injection

-LRB-

h

-RRB-

-LRB-

-RRB-

Duration

of

acquisition

-LRB-

min

-RRB-

-LRB-

-RRB-

Data

are

presented

as

mean

standard

deviation

-LRB-

range

-RRB-

NYHA

New

York

Heart

Association

LVEF

left

ventricular

ejection

fraction

Isch

ischemic

Non-isch

non-ischemic

LEGP

low-energy

all

purpose

LEHR

low-energy

high

resolution

ME

medium

energy

MBq

mega-Becquerel

h

hours

min

minutes.Categorical

data

-LRB-

Fisher

's

exact

test

for

each

group

-RRB-

p

p

p

Continuous

data

-LRB-

ANOVA

with

posthoc

Bonferoni

-RRB-

p

compared

to

late

H/M

p

compared

to

late

H/M

p

compared

to

late

H/M

Overall

most

acquisitions

were

performed

with

low-energy

high-resolution

-LRB-

LEHR

-RRB-

collimators

-LRB-

-RRB-

followed

by

low-energy

general

purpose

-LRB-

LEGP

-RRB-

collimators

-LRB-

-RRB-

Only

of

acquisitions

were

made

with

medium-energy

-LRB-

ME

-RRB-

collimators

all

from

one

centre

The

amount

of

activity

injected

ranged

from

to

MBq

-LRB-

mean

MBq

-RRB-

There

was

a

large

variation

in

the

time-span

after

between

injection

of

and

imaging

ranging

from

up

to

h

-LRB-

mean

delay

h

-RRB-

The

duration

of

acquisition

could

be

classified

in

seven

categories

and

min

The

majority

of

acquisitions

was

performed

with

a

duration

-LRB-

n

-RRB-

There

were

differences

between

the

three

late

H/M

groups

in

collimator

type

amount

of

injected

delay

after

injection

and

duration

of

acquisition

-LRB-

Table

-RRB-

Table

shows

the

results

of

the

stepwise

multivariate

regression

analysis

for

all

subjects

and

all

parameters

LVEF

collimator

type

duration

of

acquisition

NYHA

classification

and

age

were

independent

predictors

of

late

H/M

This

model

predicted

approximately

of

the

variation

in

late

H/M

results

-LRB-

p

-RRB-

Even

after

exclusion

of

the

very

low

acquisition

durations

-LRB-

min

-RRB-

the

duration

of

acquisition

remained

an

independent

predictor

of

late

H/M

Table

analysis

of

clinical

and

acquisition

related

parameters

as

predictors

of

late

H/M

for

all

subjects

-LRB-

N

-RRB-

VariablesCoefficient

bStandard

error

bP

value

Collimator

Duration

of

NYHA

Age

of

the

model

adjusted

P

value

In

subjects

with

a

late

H/M

stepwise

multivariate

regression

analysis

showed

that

NYHA

classification

and

delay

after

injection

were

the

only

independent

predictors

of

late

H/M

-LRB-

Table

-RRB-

This

model

predicted

approximately

of

late

H/M

-LRB-

p

-RRB-

In

subjects

with

a

late

H/M

stepwise

multivariate

regression

analysis

showed

that

LVEF

and

collimator

type

were

the

only

independent

predictors

of

late

H/M

-LRB-

Table

-RRB-

This

model

predicted

approximately

of

late

H/M

-LRB-

p

-RRB-

In

subjects

with

a

late

H/M

duration

of

acquisition

was

the

only

independent

predictor

of

late

H/M

-LRB-

Table

-RRB-

However

duration

of

acquisition

predicted

only

of

late

H/M

and

explained

a

statistically

non-significant

proportion

of

variability

-LRB-

p

-RRB-

Table

analysis

of

clinical

and

acquisition

related

parameters

as

predictors

of

late

H/M

for

subjects

with

a

late

H/M

-LRB-

N

-RRB-

VariablesCoefficient

bStandard

error

bP

value

NYHA

Delay

after

injection

of

the

model

adjusted

P

value

Table

analysis

of

clinical

and

acquisition

related

parameters

as

predictors

of

late

H/M

for

subjects

with

a

late

H/M

-LRB-

N

-RRB-

VariablesCoefficient

bStandard

error

bP

value

Collimator

of

the

model

adjusted

P

value

Table

analysis

of

clinical

and

acquisition

related

parameters

as

predictors

of

late

H/M

for

subjects

with

a

late

H/M

-LRB-

N

-RRB-

VariablesCoefficient

bStandard

error

bP

value

Duration

of

acquisition0.1190.0570.040Goodness-of-fit

of

the

model

adjusted

P

value

Discussion

In

a

heterogeneous

population

of

heart

failure

patients

the

most

important

determinant

of

cardiac

uptake

of

is

the

degree

of

impairment

of

the

NE

transporter

function

in

presynaptic

adrenergic

neurons

-LSB-

-RSB-

As

such

considerable

variation

in

late

H/M

would

be

expected

between

patients

with

otherwise

similar

clinical

presentations

-LRB-

NYHA

class

LVEF

etc

-RRB-

Nevertheless

the

findings

of

the

present

study

indicate

that

a

proportion

of

the

variation

in

the

late

H/M

can

also

be

explained

by

differences

in

acquisition

parameters

Of

particular

interest

the

factors

contributing

to

this

variation

differed

for

different

ranges

of

late

H/M

Abnormalities

in

myocardial

imaging

have

been

demonstrated

in

patients

with

both

common

cardiac

pathologies

such

as

CAD

CHF

and

non-ischemic

cardiomyopathy

-LSB-

-RSB-

and

more

uncommon

entities

such

as

Syndrome

X

-LSB-

-RSB-

Brugada

Syndrome

-LSB-

-RSB-

and

idiopathic

ventricular

fibrillation

-LSB-

-RSB-

However

there

has

been

limited

standardisation

of

the

acquisition

and

quantitative

analysis

techniques

used

by

various

investigators

and

most

studies

have

involved

small

numbers

of

subjects

and

locally

defined

reference

standards

and

measures

of

outcome

Thus

despite

the

large

number

of

studies

on

cardiac

imaging

these

methodological

and

analytical

limitations

have

hampered

the

implementation

of

this

technique

for

the

evaluation

and

management

of

individual

patients

Acquisition

duration

was

one

of

the

independent

predictors

of

late

H/M

The

positive

correlation

suggests

that

a

longer

acquisition

time

is

associated

with

a

higher

late

H/M

However

it

is

more

likely

that

this

association

reflects

that

a

longer

acquisition

time

results

in

a

higher

number

of

counts

and

the

allied

improvement

of

count

statistics

In

particular

in

patients

with

reduced

myocardial

uptake

-LRB-

i.e.

heart

failure

patients

-RRB-

the

higher

signal-to-noise

ratio

for

a

longer

acquisition

-LRB-

min

in

the

present

study

-RRB-

plays

a

pivotal

role

in

the

accurate

assessment

of

late

H/M

In

addition

delay

after

injection

was

in

high-risk

subjects

-LRB-

late

H/M

-RRB-

an

independent

predictor

of

late

H/M

The

negative

correlation

suggests

that

a

longer

acquisition

time

is

associated

with

a

lower

late

H/M

However

in

analogy

to

acquisition

duration

it

is

more

likely

that

this

association

reflects

that

a

longer

delay

results

in

a

lower

number

of

counts

and

the

allied

deterioration

of

count

statistics

In

particular

in

patients

with

reduced

myocardial

uptake

-LRB-

i.e.

heart

failure

patients

-RRB-

the

higher

signal-to-noise

ratio

for

a

shorter

delay

after

injection

plays

a

pivotal

role

in

the

accurate

assessment

of

late

H/M

The

most

well-validated

influence

on

the

measured

late

H/M

is

the

collimator

type

Because

of

the

high-energy

photons

emitted

by

septal

penetration

affects

estimation

of

the

H/M

ratio

in

imaging

with

a

low-energy

-LRB-

LE

-RRB-

collimator

-LSB-

-RSB-

Medium-energy

-LRB-

ME

-RRB-

collimators

have

been

shown

to

improve

quantitative

accuracy

in

studies

-LSB-

-RSB-

While

these

results

would

suggest

that

semi-quantitative

cardiac

imaging

might

best

be

performed

using

ME

collimators

there

are

practical

limitations

to

such

a

recommendation

Almost

all

nuclear

cardiology

procedures

are

now

performed

on

a

multi-head

gamma

camera

and

many

dedicated

dual-head

cardiac

cameras

are

not

supplied

with

ME

collimators

-LRB-

at

least

for

SPECT

-RRB-

The

precise

impact

of

collimator

choice

on

the

prognostic

value

has

not

been

evaluated

yet

However

it

seems

feasible

that

the

improved

accuracy

of

the

ME

collimators

will

decrease

the

number

of

patients

with

an

intermediate

risk

likelihood

and

thereby

improving

the

prognostic

accuracy

of

myocardial

uptake

parameters

of

It

is

therefore

important

to

establish

the

degree

to

which

the

collimator

used

affects

prognostic

utility

of

the

H/M

measurement

Rigorous

and

uniform

analysis

of

cardiac

parameters

minimises

inter-and

intra-individual

variation

-LSB-

-RSB-

In

the

analysis

of

the

entire

population

numerous

variables

-LRB-

LVEF

collimator

type

duration

of

acquisition

NYHA

classification

and

age

-RRB-

contributed

to

the

prediction

of

H/M

but

only

two

of

these

variables

are

under

the

control

of

the

imager

Furthermore

the

present

results

suggest

that

the

severity

of

cardiac

sympathetic

neuronal

dysfunction

also

modulates

the

impact

of

acquisition

parameters

on

the

H/M

determinations

For

example

in

the

low-risk

group

-LRB-

H/M

-RRB-

of

the

parameters

had

a

meaningful

impact

on

the

numerical

result

indicating

that

preserved

myocardial

uptake

of

can

be

reliably

determined

under

widely

different

acquisition

conditions

By

comparison

considering

user-controlled

variables

assessment

of

high-risk

subjects

-LRB-

H/M

-RRB-

was

affected

by

delay

after

injection

while

the

assessment

of

H/M

in

the

intermediate

risk

subjects

was

affected

by

the

collimator

employed

Standardisation

therefore

is

most

important

in

assessing

patients

with

more

severe

disease

although

in

the

present

study

the

procedural

variables

only

contributed

a

relatively

small

fraction

of

the

overall

variability

in

H/M

determinations

Aging

is

associated

with

changes

in

the

cardiovascular

autonomic

regulation

both

under

resting

and

stimulated

conditions

At

rest

elderly

subjects

show

increased

sympathetic

and

decreased

parasympathetic

activity

as

well

as

impaired

arterial

baroreflex

function

-LSB-

-RSB-

The

negative

correlation

although

weak

between

age

and

late

H/M

is

in

line

with

the

finding

that

sympathetic

activity

increases

with

age

typically

reflected

by

increased

circulating

catecholamine

levels

and

that

it

is

associated

with

decreased

myocardial

uptake

of

an

observation

previously

reported

by

Somsen

et

al.

-LSB-

-RSB-

and

Estorch

et

al

-LSB-

-RSB-

has

been

shown

by

individual

centres

to

have

both

good

reproducibility

and

acceptable

variability

and

to

have

prognostic

value

in

CHF

patients

-LSB-

-RSB-

These

single-centre

experiences

however

do

not

necessarily

allow

for

extrapolation

of

the

obtained

results

to

other

centres

In

spite

of

this

quantitative

thresholds

are

often

implemented

without

inter-institutional

validation

Because

there

are

differences

between

centres

in

hardware

acquisition

parameters

and

post-acquisition

processing

the

extrapolation

to

other

centres

or

generalisation

of

these

single-centre

findings

is

not

per

se

justified

Especially

due

to

the

lack

of

well-defined

data

sets

validation

in

each

separate

centre

and

between

centres

has

not

been

possible

Recently

a

realistic

cardiac

phantom

the

Amsterdam

gated

cardiac

phantom

-LRB-

AGATE

phantom

-RRB-

was

developed

and

validated

-LSB-

-RSB-

Such

a

phantom

could

be

used

as

a

tool

for

the

validation

in

each

separate

centre

and

for

standardisation

between

centres

However

a

phantom

can

only

partially

simulate

patient

characteristics

Therefore

the

phantom

results

obtained

will

give

only

an

impression

of

repeatability

and

variability

but

they

do

not

necessarily

reflect

the

accuracy

of

measurements

in

patients

Therefore

in

addition

to

the

phantom

measurements

a

set

of

reference

patient

studies

should

also

be

included

in

a

validation

of

the

technique

-LSB-

-RSB-

Moreover

the

results

should

be

validated

in

each

separate

centre

and

monitored

for

reproducibility

and

consistency

Several

medications

used

to

treat

patients

with

heart

failure

may

influence

myocardial

uptake

However

in

our

study

the

data

on

medication

use

were

relatively

complete

available

for

about

of

the

study

subjects

so

any

further

analysis

could

only

be

based

on

this

subset

The

problem

with

pursuing

a

medication

analysis

is

that

any

effect

on

uptake

is

related

to

individual

physiology

and

efficacy

of

treatment

rather

than

on

the

technical

attributes

of

the

imaging

which

was

the

main

focus

of

this

manuscript

In

addition

the

main

manuscript

already

included

results

examining

these

effects

specifically

that

subjects

that

had

events

were

less

likely

to

be

on

β-blockers

than

those

who

did

not

have

events

-LSB-

-RSB-

A

specific

analysis

of

the

effect

of

medication

was

not

deemed

appropriate

to

this

manuscript

In

addition

the

use

of

medication

that

interferes

with

myocardial

uptake

of

-LRB-

such

as

tricyclic

antidepressants

-RRB-

was

not

significant

and

did

not

warrant

a

separate

analysis

The

primary

limitation

of

the

present

study

has

already

been

noted

namely

that

the

largest

influence

on

the

H/M

is

cardiac

disease

status

rather

than

image

acquisition

parameters

Although

collimation

and

acquisition

duration

were

independent

predictors

of

late

H/M

their

individual

contributions

to

measurement

variance

were

each

Because

of

the

retrospective

nature

of

this

multi-centre

study

it

was

not

possible

to

control

for

the

effects

of

numerous

variables

that

might

have

had

undetected

impact

on

late

H/M

Studies

using

phantoms

have

already

established

the

effect

of

collimator

selection

on

H/M

and

similar

studies

could

be

performed

to

examine

the

influence

of

count

rate

and

total

counts

Additional

patient

studies

that

included

multiple

acquisitions

of

different

durations

and

times

post-injection

could

establish

the

effect

of

these

parameters

on

H/M

with

greater

clarity

In

conclusion

the

limited

standardisation

in

acquisition

parameters

reported

in

literature

was

also

reflected

in

the

results

of

this

multi-centre

study

A

wide

variety

of

collimators

delay

after

injection

of

to

the

start

of

the

acquisition

and

acquisition

durations

were

reported

In

general

validation

and

standardisation

require

commitment

and

perseverance

Moreover

without

proper

validation

and

standardisation

the

role

myocardial

in

the

clinical

management

of

CHF

will

continue

to

be

constrained

Without

these

requirements

the

use

of

myocardial

will

be

limited

to

a

single

centre

research

tool

for

understanding

the

physiology

of

myocardial

sympathetic

neuronal

activity

under

different

conditions

and

after

interventions

With

application

of

appropriate

standardisation

myocardial

imaging

could

become

a

routine

procedure

for

evaluation

of

heart

failure

and

other

cardiac

disease

populations

O O O O B O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O


Auditory grouping occurs prior to intersensory pairing : evidence from temporal ventriloquism The authors examined how principles of auditory grouping relate to intersensory pairing . Two sounds that normally enhance sensitivity on a visual temporal order judgement task -LRB- i.e. temporal ventriloquism -RRB- were embedded in a sequence of flanker sounds which either had the same or different frequency -LRB- Exp . 1 -RRB- , rhythm -LRB- Exp . 2 -RRB- , or location -LRB- Exp . 3 -RRB- . In all experiments , we found that temporal ventriloquism only occurred when the two capture sounds differed from the flankers , demonstrating that grouping of the sounds in the auditory stream took priority over intersensory pairing . By combining principles of auditory grouping with intersensory pairing , we demonstrate that capture sounds were , counter-intuitively , more effective when their locations differed from that of the lights rather than when they came from the same position as the lights . Introduction Sense organs like the ears and eyes are continuously bombarded with information . Yet , observers perceive distinct objects or events . The way information is assigned to objects has , for vision , been described with Gestalt principles like ` similarity ' , ` good continuation ' , or ` common fate ' , and similar principles have also been discovered for audition -LRB- Bregman 1990 -RRB- . It occurs , for instance , when a sequence of alternating high - and low-frequency tones is played at a certain rate . When the frequency difference between the tones is small , listeners group the tones into a single stream , but at bigger frequency differences , the sequence splits into two streams , one high and one low in pitch . Typically , these grouping principles apply within a single modality like vision or audition . However , sense organs not only work in isolation , they also have to cooperate to form a coherent multisensory representation of the environment . The notion on how information from different sense organs is assigned to a multisensory event is usually referred to as the ` assumption of unity ' . It states that as events from different modalities share more amodal properties , in particular space and time , it is more likely that they originate from a common object or source -LRB- e.g. Welch and Warren 1980 ; Bedford 1989 ; Stein and Meredith 1993 ; Radeau 1994 ; Bertelson 1999 ; Welch 1999 -RRB- . Following this notion , the assignment of information from different modalities to a single multisensory event will be reduced or absent when stimuli are too far apart in space or time , because in that case two objects or events will be perceived rather than a single multimodal one . Here , we explored how principles of auditory grouping relate to intersensory pairing . Previous work on this topic suggests that auditory grouping may take priority over intersensory pairing . For example , Vroomen and de Gelder -LRB- 2000 -RRB- used a task in which participants had to detect a visual target in a rapidly changing sequence of visual distracters . They observed that a high tone embedded in a sequence of low tones enhanced detectability of a synchronously presented visual target . There was no such intersensory enhancement when the tone was embedded in a sequence of tones with the same frequency or when the tone was part of a melody . The cross-modal enhancement thus only occurred when the sound segregated from the sound sequence in which it was embedded . Similar results were obtained by Watanabe and Shimojo -LRB- 2001 -RRB- . They explored how the ` bounce illusion ' is affected by contextual auditory information . The bounce illusion is a cross-modal phenomenon in which a ` collision ' sound presented near the crossover of two moving balls enhances the perception of the balls ` bouncing ' , whereas the absence of the sound results in a ` streaming ' percept . The authors showed a reduction of the bounce illusion when the sounds were embedded in a sequence of similar sounds , as opposed to when the sounds were flanked by sounds of a different frequency . Here we tested the generality of these findings by examining how auditory grouping affects auditory -- visual -LRB- AV -RRB- pairing in the temporal domain using the so-called temporal ventriloquist effect -LRB- Scheier et al. 1999 ; Fendrich and Corballis 2001 ; Aschersleben and Bertelson 2003 ; Bertelson and Aschersleben 2003 ; Morein-Zamir et al. 2003 ; Vroomen and de Gelder 2004 ; Stekelenburg and Vroomen 2005 ; Vroomen and Keetels 2006 -RRB- . Temporal ventriloquism refers to the phenomenon that when a sound and light are presented at slightly different onset times -LRB- usually in the order of ∼ 100 ms -RRB- , the sound will attract the temporal occurrence of the light . This phenomenon can be demonstrated in a visual temporal order judgment -LRB- TOJ -RRB- task in which participants are presented two lights at various stimulus onset asynchronies -LRB- SOAs -RRB- and judge , which came first . By presenting a sound before the first and after the second light , the just noticeable difference -LRB- JND -RRB- improves -LRB- i.e. , participants become more sensitive -RRB- , presumably because the two sounds attract the temporal occurrence of the two lights , and thus effectively pull the lights further apart in time -LRB- Scheier et al. 1999 ; Morein-Zamir et al. 2003 ; Vroomen and Keetels 2006 -RRB- . Judgments about which light came first are therefore more accurate if there is a ∼ 100 ms interval between the sounds and lights rather than when the sounds are presented simultaneously with the lights . Here we asked what happens if the sounds that capture the onset of the lights are assigned to a stream of other sounds with which they form a well-formed sequence . If auditory grouping takes priority over intersensory pairing , one expects an improvement on the visual TOJ task only if the capture sounds segregate from the auditory stream . Alternatively , though , audio -- visual pairing might take priority over auditory grouping in which case observers should improve on the visual TOJ task no matter whether the sounds segregate or not . In Experiment 1 , these predictions were tested with two capture sounds that were embedded in a sequence of flanker sounds , which either had the same or a different frequency . When the frequency of the flanker and the capture sounds were the same , the sequence was heard as a single stream which , following previous findings -LRB- Vroomen and de Gelder 2000 ; Watanabe and Shimojo 2001 -RRB- , should prevent temporal ventriloquism to occur . When the flankers differed from the capture sounds , stream segregation was more likely to occur in which case the two sounds could possibly interact with the lights and thus improve performance on the visual TOJ task . Other stream segregation cues besides the frequency of the flanker and capture sounds were further explored in Experiment 2 -LRB- rhythm -RRB- and Experiment 3 -LRB- sound location -RRB- . Experiment 1 : Capture and flanker sounds with the same or different frequency Participants performed a visual TOJ task in which they decided which of two lights appeared first . Two task-irrelevant high tones were presented either simultaneously with the lights -LRB- i.e. , the ∼ 0 ms AV interval -RRB- , or the first tone was presented ∼ 100 ms before the first light and the second tone ∼ 100 ms after the second light -LRB- i.e. , the ∼ 100 ms AV interval -RRB- . The two high tones were embedded in a sequence of other tones , which either had the same -LRB- high -RRB- or a different -LRB- low -RRB- frequency -LRB- see Fig. 1a for a schematic overview of the conditions -RRB- . Fig. 1a A schematic illustration of a trial . Lights were presented with a particular SOA ranging between − 75 and 75 ms , with negative values indicating that the lower light was presented first . Two capture sounds were presented either simultaneously with the lights -LRB- ∼ 0 ms AV-interval -RRB- , or ∼ 100 ms before the first and ∼ 100 ms after the second light -LRB- ∼ 100 ms AV-interval -RRB- . The capture sounds were embedded in a sequence of flanker sounds which either had the same or a different frequency -LRB- Exp1 -RRB- , rhythm -LRB- Exp 2 -RRB- , or location -LRB- Exp 3 -RRB- . Perceptual grouping of the sounds is illustrated by the grey ovals . Temporal ventriloquism only occurred when the capture sounds were different from the flanker sounds at the ∼ 100 ms interval , as illustrated on the second line . b Schematic set-up of Experiment 1 , 2 and 3 Method Participants Thirteen students from Tilburg University were given course credits for their participation . All reported normal hearing and normal or corrected-to-normal seeing . They were tested individually and were unaware of the purpose of the experiment . The experimental procedures were approved by the Institute and were in accordance with Declaration of Helsinki . Stimuli Two auditory stimuli , a low -LRB- 1,500 Hz -RRB- and a high -LRB- 3,430 Hz -RRB- pure tone of 3 ms at 72 dB -LRB- A -RRB- were used that clearly differed in pitch . The sounds were presented via a hidden loudspeaker located at eye-level , at central location and at 90 cm distance . Visual stimuli were presented by two red LEDs -LRB- diameter of 1 cm , luminance of 40 cd/m2 -RRB- , positioned 5 ° below and above the central loudspeaker . A small green LED was placed at the center of the loudspeaker and served as a fixation point -LRB- see Fig. 1b for a schematic set-up -RRB- . Trials in the ∼ 0 ms AV interval consisted of a sound sequence of 40 sounds in which the interval between the successive tones was equal to the SOA between the two lights . The lights were presented simultaneously with the 25th and 26th sound . Trials in the ∼ 100 ms AV-interval consisted of a tone sequence of 15 sounds with the interval between the tones equal to the SOA of the lights plus 200 ms. The two lights were presented in the middle of the temporal gap , ∼ 100 ms after the 10th and ∼ 100 ms before the 11th sound . Design The experiment had three within-subjects factors : Frequency of the flanker sounds -LRB- same or different frequency as the capture sounds -RRB- , the AV-interval between the capture sounds and the lights -LRB- ∼ 0 or ∼ 100 ms -RRB- , and the SOA between the two lights -LRB- − 75 , − 60 , − 45 , − 30 , − 15 , +15 , +30 , +45 , +60 , and +75 ms ; with negative values indicating that the lower light was presented first -RRB- . These factors yielded 40 equi-probable conditions , each presented 20 times for a total of 800 trials -LRB- 10 blocks of 80 trials each -RRB- . Procedure Participants sat at a table in a dimly lit and soundproof booth . The fixation light was illuminated at the beginning of the experiment , and participants were instructed to maintain fixation on this central green LED during testing . The participant 's task was to judge whether the lower or the upper LED was presented first . Responses -LRB- unspeeded -RRB- were made by pressing one of two designated keys with the right thumb -LRB- lower light first -RRB- or right index -LRB- upper light first -RRB- . Whenever a response was detected , both LEDs were turned off and the next trial started after 2,000 ms. A practice block was included consisting of 16 trials in which the four longest SOAs were presented once in each condition . During practice , participants received verbal feedback -LRB- `` Correct '' or `` Wrong '' -RRB- . Results and discussion Trials of the practice session were excluded from analyses . The proportion of ` up-first ' responses was calculated for each condition and converted into equivalent Z-scores assuming a cumulative normal distribution -LRB- cf. Finney 1964 -RRB- . For each of the four conditions , the best-fitting straight line was calculated over the ten SOAs . The lines ' slopes and intercepts were used to determine the point of subjective simultaneity -LRB- PSS -RRB- and the just noticeable difference -LRB- JND = 0.675 / slope -RRB- . The PSS represents the average interval by which the upper stimulus had to lead the lower one in order to be perceived as simultaneous . The JND represents the smallest interval between the onsets of the two lights needed for participants to correctly judge which stimulus had been presented first on 75 % of the trials . Temporal ventriloquism was measured by subtracting the JND in the ∼ 100 ms AV interval from the ∼ 0 ms AV interval -LRB- see Table 1 for the average JNDs -RRB- . Table 1Mean just noticeable differences -LRB- JND -RRB- in ms , and standard errors of the mean -LRB- in parentheses -RRB- of Experiment 1 and 2Flanker soundsSame as capture soundsDifferent from capture soundsExperiment AV-interval -LRB- ms -RRB- JNDTVEJNDTVEExp 1 -LRB- Frequency -RRB- 021.0 -LRB- 0.8 -RRB- 0.522.1 -LRB- 1.1 -RRB- 3.8 * 10020.5 -LRB- 1.1 -RRB- 18.3 -LRB- 0.7 -RRB- Exp 2 -LRB- Rhythm -RRB- 029.1 -LRB- 2.5 -RRB- − 3.723.9 -LRB- 1.9 -RRB- 3.6 * 10032.8 -LRB- 2.5 -RRB- 20.3 -LRB- 0.8 -RRB- Capture Sounds Presented at ∼ 0 or ∼ 100 ms audio -- visual intervals ; flanker Sounds with the same or different frequency -LRB- Exp 1 -RRB- or rhythm -LRB- Exp 2 -RRB- as capture sounds . The temporal ventriloquist effect -LRB- TVE -RRB- is the improvement in JND between the ∼ 0 and ∼ 100 ms audio -- visual intervals * P < 0.05 A 2 × 2 ANOVA with as within-subjects factors the frequency of the flanker sounds -LRB- same or different frequency as the capturer sounds -RRB- and the AV-interval -LRB- ∼ 0 and ∼ 100 ms -RRB- was conducted on the JNDs and PSSs . In the ANOVA on the PSSs , no effect was significant -LRB- all P 's > 0.30 -RRB- , which is in line with our expectations since no shift towards more ` up ' or ` down ' responses was expected . In the ANOVA on the JNDs , the important interaction between the AV-interval and the frequency of the flanker sounds was significant , F -LRB- 1 , 12 -RRB- = 4.90 , P < 0.05 . Separate t tests comparing the ∼ 0 ms AV interval with the ∼ 100 ms AV interval showed that JNDs improved by 3.8 ms when the frequency of the capture and flanker sounds differed , t -LRB- 12 -RRB- = 3.06 , P < 0.01 , but no significant difference was obtained -LRB- 0.5 ms -RRB- when the capture and flanker sounds were the same , t -LRB- 12 -RRB- = 0.71 , P = 0.49 . As predicted , temporal ventriloquism thus only occurred when the capture and flanker sounds differed . It seems therefore likely that segregation of the capture sounds from the flankers was necessary before the capture sounds could interact with the lights . When the capture and flanker sounds were the same , auditory grouping thus took priority over AV pairing . Experiment 2 : Capture and flanker sounds with the same or different rhythm To further explore the relation between auditory grouping and intersensory pairing , we presented the capture sounds in or out of rhythm with the flankers . Rhythm is , besides frequency , another important auditory segregation cue -LRB- Bregman 1990 -RRB- . It was expected that sounds presented out of rhythm would segregate from the sound sequence , thus enhancing performance on the visual TOJ task . Capture sounds presented in rhythm should not segregate from the auditory stream , and they should thus have no effect on the visual TOJ task . Method Participants Twenty new students participated . Stimuli and design Stimuli and design were as in Experiment 1 , except that the time interval between the capture and flanker sounds was varied rather than their frequency . The auditory stimuli consisted of 5 m s sound bursts presented at 72 dB -LRB- A -RRB- . When the capture sounds were presented in rhythm with the flankers , the same interval between consecutive sounds in the sequence was used as in Experiment 1 -LRB- i.e. , SOA between the two lights + 2 × AV-interval -RRB- . When the capture sounds were presented out of rhythm , the interval between the capture and flanker sounds was increased , such that there was a short pause before the first and after the second capture sound . In the ∼ 0 ms AV-interval condition , the two longer intervals were 8 × SOA of the lights , in the ∼ 100 ms AV-interval condition they were 17 × SOA of the lights +200 ms. Results and discussion In the 2 -LRB- Capture sounds in or out of rhythm -RRB- × 2 -LRB- AV-interval ∼ 0 or ∼ 100 ms -RRB- ANOVA on the PSSs , no effect was significant -LRB- all P 's > 0.30 -RRB- . The same ANOVA on the JNDs showed that the important interaction between AV-interval and rhythm was significant , F -LRB- 1 , 19 -RRB- = 15.35 , P < 0.001 . Separate t tests showed that the 3.6 ms temporal ventriloquist effect -LRB- lower JNDs in the ∼ 100 ms AV interval rather than ∼ 0 ms -RRB- of sounds presented out of rhythm was significant , t -LRB- 19 -RRB- = 2.37 , P < 0.05 . Performance got actually worse -LRB- − 3.7 ms -RRB- when the capture sounds were presented in the same rhythm as the flanker sounds , t -LRB- 19 -RRB- = − 2.15 , P < 0.05 . Capture sounds thus again only improved performance on the visual TOJ task when they segregated from the flanker sounds . Experiment 3 : Capture and flanker sounds from the same or different location It is known that auditory stream segregation may also occur when there is a difference in the location of consecutive sounds -LRB- Bregman 1990 -RRB- . In Experiment 3 , we therefore varied the location of the capture and flanker sounds . The sounds could emanate either from a central loudspeaker near the two lights , or from a lateral loudspeaker on the far left or far right . If intersensory pairing only occurs when the capture sounds segregate from the flankers , then temporal ventriloquism should be obtained when the locations of the capture and flanker sound differ , but not when they are the same . This set-up also allowed us to explore whether spatial disparity between the capture sounds and lights affects intersensory pairing . The common notion on intersensory pairing states that commonality in space between the auditory and visual signal matters . However , in contrast with this notion , it has recently been shown that temporal ventriloquism may not be affected by spatial discordance between the sounds and lights . In a study by Vroomen and Keetels -LRB- 2006 -RRB- , it was shown that there were equal amounts of temporal ventriloquism when the two capture sounds came from the same or a different position as the lights , when the sounds were static or moved , or when the sounds and lights came from the same or opposite sides of fixation . Assuming that these results would be replicated in the present set-up as well , we expected sound location to be unimportant for intersensory pairing . Equal amounts of temporal ventriloquism were therefore expected from segregated sounds presented from the central location -LRB- near the lights -RRB- and the lateral location -LRB- far from the lights -RRB- . The notion that sound location matters for auditory grouping , but not for intersensory pairing also lead to a very counter-intuitive prediction . In case flanker sounds were presented near the central lights , there should more temporal ventriloquism by capture sounds presented from a lateral position than from central position , because only the lateral sounds segregate . With central flankers , there should thus be more temporal ventriloquism when the location of the sounds and lights differ , rather then when they are the same . Method Participants , stimuli and procedures were the same as in Experiment 1 , except for the following changes . Eighteen new students from the same subject pool participated . The auditory stimuli consisted of 5 ms sound bursts presented at 72 dB -LRB- A -RRB- , presented from one of two loudspeakers -LRB- see Fig. 1b -RRB- . One speaker was located at central location at eye-level and at 90 cm distance -LRB- as in Experiments 1 and 2 -RRB- , the other was located on either the far left or the far right -LRB- at 90 ° azimuth -RRB- . Four within-subjects factors were used : Location of the two capture sounds -LRB- central or lateral -RRB- , Location of the flanker sounds -LRB- same or different position as the capture sounds -RRB- , the AV-interval between the capture sounds and lights -LRB- ∼ 0 or ∼ 100 ms -RRB- , and the SOA between the two lights -LRB- − 75 to +75 ms -RRB- . The 80 conditions were each presented 20 times in 10 blocks of 160 trials each . In half of the blocks , the lateral speaker was on the left , in the other half it was on the right . Results A 2 × 2 × 2 ANOVA with as within-subjects factors Location of the two capture sounds -LRB- central or lateral -RRB- , location of the flanker sounds -LRB- same or different position as the capture sounds -RRB- and the AV interval -LRB- ∼ 0 and ∼ 100 ms -RRB- was conducted on the JNDs and PSSs . In the ANOVA on the PSS , there was an interaction between the location of the capture and flanker sounds , F -LRB- 1 , 17 -RRB- = 6.31 , P < 0.025 , indicating that there were slightly more ` up ' responses in trials in which the capture and flanker sounds were presented centrally -LRB- mean PSS = − 1.84 ms -RRB- rather than in the other conditions -LRB- mean PSS = 2.61 ms -RRB- , a finding for which there is no clear explanation . In the ANOVA on the JNDs -LRB- see Table 2 -RRB- there was no main effect of the location of the capture sounds , F -LRB- 1 , 17 -RRB- = 1.67 , P = 0.21 , indicating that JNDs were unaffected by whether the capture sounds were presented centrally -LRB- near the two lights -RRB- or laterally . Most importantly , there was an interaction between the AV-interval and the location of the flanker sounds , F -LRB- 1 , 17 -RRB- = 5.11 , P < 0.05 . Separate t tests confirmed that the temporal ventriloquist effect -LRB- better performance at ∼ 100 ms rather than ∼ 0 ms AV interval -RRB- was only significant when the flanker sounds came from a different position than the capture sounds . There was thus no temporal ventriloquism when the capture and flanker sounds came both from central or lateral positions -LRB- both P 's > 0.6 -RRB- , while there was a 3.9 ms improvement for central capture sounds with lateral flankers , t -LRB- 17 -RRB- = 2.175 , P < 0.05 , and a 3.1 ms improvement for lateral capture sounds with central flankers , t -LRB- 17 -RRB- = 2.55 , P < 0.025 . These two improvements were not significantly different from each other , t -LRB- 17 -RRB- = 0.52 , P = 0.60 . Moreover , as predicted , with central flankers , temporal ventriloquism by lateral capture sounds was bigger than that from central ones , t -LRB- 18 -RRB- = 1.798 , P < 0.05 . Table 2Mean just noticeable differences -LRB- JND -RRB- in ms , and standard errors of the mean -LRB- in parentheses -RRB- of Experiment 3Location of flanker soundsSame as capture soundsDifferent from capture soundsLocation of capture soundsAV-interval -LRB- ms -RRB- JNDTVEJNDTVECentral028 .2 -LRB- 2.1 -RRB- − 0.927.7 -LRB- 2.0 -RRB- 3.9 * 10029.1 -LRB- 2.3 -RRB- 23.8 -LRB- 1.4 -RRB- Lateral030 .0 -LRB- 2.2 -RRB- 1.729.0 -LRB- 1.8 -RRB- 3.1 * 10028.3 -LRB- 2.0 -RRB- 25.9 -LRB- 1.8 -RRB- Capture Sounds Presented at ∼ 0 or ∼ 100 ms audio -- visual intervals from central or lateral location ; flanker sounds presented from the same or different location as the capture sounds . The temporal ventriloquist effect -LRB- TVE -RRB- is the improvement in JND between the ∼ 0 and ∼ 100 ms audio -- visual intervals * P < 0.05 General discussion This study examined how principles of auditory grouping relate to intersensory pairing . Two capture sounds that normally enhance performance on a visual TOJ task -LRB- i.e. temporal ventriloquism -RRB- were embedded in a sequence of flanker sounds which could differ in frequency -LRB- Exp . 1 -RRB- , rhythm -LRB- Exp . 2 -RRB- , or location -LRB- Exp . 3 -RRB- . In all experiments , we found that temporal ventriloquism only occurred when the capture sounds differed from the flankers , and there was thus no effect when flanker and capture sounds were the same . Presumably , when the capture sounds differ , they segregate from the auditory stream , and only then they can be paired cross-modally with the lights . When the two capture sounds do not differ from the flankers , they are perceptually grouped in an auditory stream , in which case they lose their saliency and can not interact cross-modally anymore . These results are similar to previous findings , which have shown that intersensory interactions do not occur when sounds that normally enhance performance belong to another auditory group -LRB- Vroomen and de Gelder 2000 ; Watanabe and Shimojo 2001 ; See also Sanabria et al. 2004a , b -RRB- . The results also imply that a sound can only be assigned to a single event : it either belongs to the auditory stream , or it is paired with the lights , but it can not be assigned to both simultaneously . In this respect , it is analogous to many of the well-known ambiguous figure-ground displays -LRB- e.g. , the Face-Vase illusion or the Necker cube -RRB- , where it is known that only one interpretation of the scene can be maintained . Another important finding was that commonality in space between the capture sounds and lights did not affect temporal ventriloquism . The temporal ventriloquist effect was thus equally big for segregated capture sounds that were presented near the lights or far away from the lights . A few other studies have demonstrated before that spatial disparity between sound and vision may not affect intersensory interactions -LRB- Welch et al. 1986 ; Bertelson et al. 1994 ; Stein et al. 1996 ; Colin et al. 2001 ; Murray et al. 2004 ; Vroomen and Keetels 2006 -RRB- . However , these studies always relied on null-effects , which entails the danger that they simply lacked the power to detect any effect of spatial disparity . Participants in previous studies might , for example , not have been able to perceive spatial disparity , or they might have learned to ignore it in the experimental task . Our findings , though , counter these arguments . By combining principles of auditory grouping with intersensory pairing , we were able to create a situation where the capture sounds were actually more effective when their locations differed from that of the lights rather than when they came from the same position as the lights . Within the same experimental situation , we thus demonstrated that sound location mattered for auditory grouping , but not for intersensory pairing . Such a finding makes it highly unlikely that sound location was not perceived or simply ignored . Rather , it becomes more likely that , at least in the temporal ventriloquist situation , commonality in space between sound and vision is not relevant for AV pairing . This may , at first sight , seem unlikely , because after all , most natural multisensory events are spatially an temporally aligned , except for some minor variations in time or space that people are readily able to adjust -LRB- e.g. Vroomen et al. 2004 -RRB- . However , a critical assumption that underlies the idea of spatial correspondence for intersensory pairing is that space has the same function in vision and audition . This notion , though , is arguable as it has been proposed that the role of space in hearing is only to steer vision -LRB- Heffner and Heffner 1992 -RRB- , while in vision it is an indispensable attribute -LRB- Kubovy and Van Valkenburg 2001 -RRB- . If one accepts that auditory spatial perception evolved for steering vision , but not for deciding whether sound and light belong together , there is no reason why intersensory interactions would require spatial co-localization . Our results therefore have also important implications for designing multimodal devices or creating virtual reality environments , as they show that the brain can , at least in some cases , ignore intersensory discordance in space .

B I O O O B I O O O B I O O O O O O B I O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O O O O O B I O O O O B I O O O O 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I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

auditory grouping
intersensory pairing
temporal order judgment
temporal ventriloquism