SCIENCE
Electrode alignm ent
CORTICAL SENSITIVITY TO BINAURAL
amplitude-modulated sounds
E^j News / At the heart of the matter / Wide Angle / Another Perspective / The Specialists / RESEARCH AND DEVELOPMENT
Each year a t the British A ca d em y
of A udiology conference, nearly
100 posters are presented a b o u t
th e latest research projects th a t
have been undertaken. Prizes are
aw arded by a panel of judges a n d
this year there were joint winners.
The following report is from o n e of
th e w inning projects th a t looked a t
cortical sensitivity.
I
T
By L A. Hill+, I. Yasin* and A. Faulkneri
lawrence. [email protected]. uk
h e b u rd e n o f re s e a rc h in to th e b e n e fits
stim uli, however, it m ay be m ore a p p ro p ria te to obtain
o f b ila t e r a l c o c h le a r I m p la n t a t io n h a s
a m easure of the cBI to m odulated stim uli sim ilar to that
d e m o n s t r a t e d c le a r a d v a n ta g e s o v e r
p ro du ced by the speech processor of a coch le ar im plant.
m o n a u ra l Im p la n ta tio n . T h e b in a u ra l in p u t
T h e a im o f th e s tu d y w a s to m e a s u re th e c o rtic a l
p ro vid e s e n h a n c e d s o u n d lo c a liz a tio n and
B in a u ra l In te ra c tio n u s in g m o d u la te d s tim u li w ith
im p ro v e d s p e e c h p e rc e p tio n in noise. B u t
d iffe ring degrees o f interaural m ism a tch betw een carrier
o u t o f th is e n h a n c e m e n t in he aring a b ility c o m e s th e
fre q u e n cie s and m o d u la tio n depth.
p o s s ib ility o f an e le c tric a lly -in d u c e d p itc h m is m a tc h
T h e v a lu e o f th e cB I m ay be e x p e c te d to be la rge st
a c ro ss th e ears, cre a te d by th e in s e rtio n to d iffe re n t
w h e n th e re is m in im a l m is m a tc h In in te ra u ra l c a rrie r
d e p th s a lo n g th e c o c h le a o f each electrod e. T h is can
fre q u e n c y and m o d u la tio n d e p th , a n d sm a lle st w h e n
cause a de g ra d a tio n o f the very benefits ga in ed by the
the re Is a large m ism a tch in interaural c a rrier fre q u e n cy
bilateral im plantation. The research tha t w as un de rta ken
and m o d u la tio n depth.
w as to fin d an o b je ctive way o f align in g th e electrod es
w ith o u t th e need fo r th e p a rticip a tio n o f th e im plantee.
Methodology
O bje ctive EEG (E le ctro e n ce p h a lo g ra p h y) m easures of
C o rtic a l EEG re s p o n s e s w e re o b ta in e d In re s p o n s e
b in a u ra l in te ra ctio n have m o st o fte n b e en m e a su re d
to 20-H z a m p litu d e -m o d u la te d stim uli, w h e re a ca rrier
u s in g th e a u d ito ry s te a d y-sta te re s p o n s e (A S S R ) o r
fre q u e n c y o f 1 kH z w as presented to th e left ear, and the
a u d ito ry bra in ste m re sp o n se (ABR). In th is study, th e
ca rrier fre q u e n cy in th e rig ht ear w as shifte d up w a rds in
c o rtica l N1-P2 response is used to ob tain a m easure of
fre q u e n c y by 20 Hz, 5 2 0 Hz, o r rem ained un shifted at
c o rtica l Binaural Interaction (cBI).
1 kH z (see Table 1 ). T here were a total o f 6 con ditions.
In a d d itio n , th e cBI has tra d itio n a lly used steady-state
A shift in interaural carrier frequencies of 20 Hz w ould be
AUDIO INFOS I N°79 I JUNE-JULY 2013
SCIENCE
Right frequency
Left modulation deph
Right modulation deph
al
1000
1000
1
1
a2
1000
1000
1
0
Berkshire Hospital in Reading. Lawrence
a3
1000
1020
1
1
works as part of a team of Clinical
a4
1000
1020
1
o
S cientists, audiologists, assistant
a5
1000
1520
1
l
a6
1000
1520
1
0
Law rence H ill is a p re-reg is tered
Audiological Scientist at the Royal
technical officers, scientist trainees and
hearing therapists.
Lawrence started his career studying
Lawrence Hill
I Condition
Left frequency
The Lead Author
and working as a CNC programmer
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Table 1: Summary of the carrier frequencies and modulation depths used in the 6 conditions.
in South Africa. Wanting more people
contact, he came to the UK in 2004 to
travel and explore different possibilities,
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which included working for Martin Baker Ejector seats.
M
After further soul searching and online personality tests
Lawrence applied to do the foundation degree in Hearing
aid Audiology through the private sector. After completing
Figure 1: Averaged
cortical data (N1-P2)
from 11 participants.
the FdSc, Lawrence wanted to study further so after
working in the NHS for a year he was accepted to do an
MSc in 2010 and started on a scientific training program.
Lawrence's research project was undertaken at UCL as
—
Condition a1
part of his dissertation for his masters degree in Audiology.
—
Condition a2
"What attracts me to audiology is the technical nature
—
Condition a3
of the work as well as the people contact. I also have
—
Condition a4
a strong desire to be of benefit to those who suffer
—
Condition a5
—
Condition a6
the most with hearing loss and am hoping to do some
Amplitude (microV)
lecturing in audiology in M alaw i, which has only a
handful of Audiologists in a country of 15 million. I live
in South Oxon with my wife, 2 children, 3 chickens and
1 cat. I am a gifted BBQer and balloon modeller and
in w h ic h carriers are interaurally m atche d in frequ en cy
hope one day to own a family of bearded Dragons!"
(1 kHz), o r s tim ulate diffe re nt interaural au d ito ry filters
(carrier fre q u e n cy diffe re nce o f 5 2 0 Hz), irrespective of
interaural m o d u la tio n de pth diffe re nce s (com p ariso n of
expected to stim ulate the sam e auditory filter at each ear,
c o n d itio n s a1 & a2 and c o n d itio n s a5 and a6).
and a shift in interaural carrier frequencies of 5 20 Hz would
H o w e v e r, th e a m p litu d e o f th e N 1 -P 2 c o m p le x is
be expected to stimulate different auditory filters at each ear.
s ig n if ic a n t ly re d u c e d w h e n th e c a r r ie r s d iff e r in
E le ven n o rm a l-h e a rin g in d iv id u a ls p a rtic ip a te d a n d
interaural fre q u e n cy by o n ly 20 Hz, in th e presence of
co rtica l E le ctro e n ce p h a lo g ra p h y (EEG) responses were
an interaural m o d ulation d e p th diffe re nce (com parison
m e a s u re d u s in g a 3 2 -e le c tro d e array. T h e s tim u lu s
o f c o n d itio n s a3 & a4).
fo r e a c h c o n d itio n w a s o f 1 -s e c o n d d u ra tio n a n d
w a s re p e a te d 3 0 0 tim e s at a level o f 65 d B S P L via
Discussion & Conclusion
References
in sert phones. T he inter-stim ulus interval w as 1-s. Eye-
T h e m a g n itu d e o f th e c B I re s p o n s e is s e n s itiv e to
Lavikainena, J, Hitmen,
e lectrod es w ere also a p p lie d to m easure horizontal and
diffe re nce s in interaural m o d ulation de p th fo r relatively
H, May, P & Naatanena, R
vertica l eye-m ovem ents.
s m a ll in te r a u r a l d iffe r e n c e s in c a r r ie r f r e q u e n c y
1997, 'Binaural interaction
T he EEG w as p ro cesse d by a p plying artefact rejection
w h ic h can be a ssu m e d to stim u la te s im ila r interaural
in the human brain can be
at a level of + 100 (J.V, ba seline corre cte d a t -100 ms, and
a u d ito ry filters. T hese results m ay provide a m eans of
non-invasively accessed
low -pass filtere d w ith a filte r c u t o ff o f 30 Hz. O c c u la r
esta blishin g an ob je ctive m easure tha t m ay be used to
with long-latency event-
artefacts w e re also rem oved using th e responses from
infer interaural co rre sp o n d e n c e fo r binaurally-presented
related potentials.'.
th e e y e -e le c tro d e s . L e ss th a n 10% o f th e d a ta w a s
m od ulated sou nd s. I
Neuroscience Letters, vol
222, p. 37-40.
rejected, and th e rem a ining data w as averaged across
Acknowledgements
runs fo r each c o n d itio n separately.
The study was approved by the UCL Ethics Board.
Joris, P, Schreiner, C & Rees,
Funded by the Royal Berkshire Hospital Foundation Trust, Reading
Results
+ The Royal Berkshire Hospital * The Ear Institute, University
A nalyses s u g g e st th a t binaural m o d u la tio n d e tection (as
C ollege London (UCL), London, UK, §Speech, Hearing and
indexed by th e N1-P2 response) is sim ila r fo r co n d itio n s
Phonetic Sciences, University College London (UCL), London, UK
A 2004, 'Neural processing
of amplitude modulating
sounds.', Physiol rev, vol 84,
pp. 541-577.
JUNE-JULY 2013 I N°79 I AUDIO INFOS E l
Scientific Focus
IIIllllll Scientific publications
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Perception of Musical Tim bre by Cochlear Implant
Listeners: A M ultidim ensional Scaling Study. Macherey O and Delpierre A. Ear Hear. 2013..
• Several stud ies have sho w n that the ability to identify
th e tim b re o f m usical instrum ents is reduced in coch le ar
im p la n t (Cl) users c o m p a re d w ith norm al-hearing (NH)
listeners. However, m ost o f these stud ies have focused
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on ta s k s th a t re q u ire s p e c ific m u sica l k n o w le d g e . In
contrast, th e present stu d y investigates th e pe rcep tion of
tim b re by Cl sub je cts using a m ultidim e nsiona l scaling
(M DS) paradigm . T he m ain objective w as to investigate
w h e th e r Cl sub je cts use the sam e cues as NH listeners
d o to differentiate the tim b re of m usical instrum ents.
designed to improve tim bre recognition in CIs will indeed
Three groups of 10 NH subjects and one group of 10 Cl
train Cl subjects to use the sam e cues as NH listeners. Fur-
s u b je c ts w e re aske d to m ake d is s im ila rity ju d g m e n ts
thermore, NH subjects listening to noise-vocoded sounds
between pairs o f instrum ental sounds. The stim uli were
ap p e a r to be a g o o d m od el o f Cl tim b re pe rcep tion as
16 synthetic instrum ent tones spanning a w ide range of
they show the sam e first tw o perceptual dim ensions as Cl
instrument families. All sounds had the sam e fundam ental
subjects d o and also exhibit a sim ilar change in perceptual
frequency (261 Hz) and were balanced in loudness and in
weights applied to these tw o dim ensions. This last finding
perceived duration before the experiment. O ne gro up of
validates the use of sim ulations to evaluate and com pare
NH subjects listened to unprocessed stimuli. The other tw o
training procedures to improve tim bre perception in CIs.
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groups of NH subjects listened to the sam e stimuli passed
through a four-channel o r an eight-channel noise vocoder,
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The a u d ito ry sen sitivity is in c rea se d in tin n itu s
designed to simulate the signal processing perform ed by a
ears. Hébert S, Fournier P, Norena A. J Neurosci. 2013 Feb
real Cl. S ubjects were presented with all possible com bina-
6;33(6):2356-64. doi: 10.1523/JNEUROSCI.3461-12.2013.
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tions of pairs of instruments and had to estimate, for each
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pair, the am ount of dissimilarity between the tw o sounds.
is a pe rvasive c o m p la in t o f p e o p le w ith tin n itu s . T h e
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Increased auditory sensitivity, also called hyperacusis,
The m odel ou tput gave, for each subject group, an opti-
h ig h p re v a le n c e o f h y p e ra c u s is in tin n itu s s u b je c ts
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mal graphical representation of the perceptual distances
s u g g e sts th a t both s ym p to m s have a c o m m o n origin.
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between stimuli (the so-called “tim bre space” ).
It has b e e n s u g g e s te d th a t th e y m a y re s u lt fro m a
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For all groups, the first tw o dim ensions of the tim bre space
m a la d ju s te d in c re a s e o f c e n tra l g a in a ttrib u ta b le to
were strikingly sim ilar and correlated strongly with the loga-
s en sory deafferentation. M ore specifically, tin n itu s and
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rithm of the attack tim e and with the center of gravity of the
hyperacusis could result from an increase of spontaneous
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spectral envelope, respectively. The acoustic correlate of the
and stim ulus-induced activity, respectively. O ne prediction
third dim ension differed across groups but only accounted
o f th is hypothesis is th a t a u d ito ry sensitivity sh o u ld be
c
fo ra s m a ll proportion o f the variance explained by the MDS
increased in tinnitus com pared with non-tinnitus subjects.
solution. Surprisingly, Cl subjects and NH subjects listening
T h e p u rp o s e o f th is s tu d y w as to te s t th is p re d ic tio n
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to noise-vocoded sim ulations gave relatively m ore weight
by e x a m in in g th e lo u d n e s s fu n c tio n s in tin n itu s ears
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to the spectral envelope dim ension and less weight to the
(n = 124) c o m p a re d w ith n o n -tin n itu s h u m a n ea rs
attack-time dim ension when m aking their judgm ents than
(n = 106). B e c a u s e tin n itu s is o fte n a c c o m p a n ie d by
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NH subjects listening to unprocessed stimuli. One possible
hearing loss and th a t hearing loss m akes it d iffic u lt to
reason fo rth e relatively higher salience of spectral envelope
d ise n ta n g le h yp erse nsitivity (hyp era cusis) to lo ud ness
cues in real and simulated CIs may be that the degradation
recruitm ent, tinn itus and non-tinnitus ears were carefully
of local fine spectral details produced a m ore stable spec-
m atched for hearing loss. O ur results show that auditory
tral envelope across the stim ulus duration.
s e n sitiv ity is e n h a n c e d in tin n itu s s u b je c ts c o m p a re d
T he internal representation o f m usical tim bre fo r isolated
with non-tinnitus subjects, including subjects with normal
musical instrum ent sounds was found to be sim ilar in NH
audiogram s. W e interpreted these fin d in g s as com patible
and in Cl listeners. This suggests that training procedures
with a m aladaptive central gain in tinnitus.
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B 3 AUDIO INFOS I N°79 I JU N E-JU LY2013