Full Name of Author â Nom complet de l'auteur. STAPELLS, D avid .... ASHA, 25, 154. (Abstract) ...... Biofeedback training of 40-Hz EEG and behavior, pp.
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260 L a u r ie r A venue O tta w a , O n ta r io ’ KIN 6 P 4 ,
A
E ast
- A pt.
5
V f
Title of Thesis — Titre d e la th e s e ,
.
t
STUDIES IN EVOKED POTENTIAL AUDIOMETRY'
University — Universite .UNIVERSITY OF OTTAWA D e g r e e (or which thesis w as p r e s e n te d — G rade p o u r lequel c e tte th e s e fut p r e se n te e P h .D .
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I
o STUDIES IN EVOKED POTENTIAL AUDIOMETRY
by
David Richard Stapells O
r A dissertation submitted to the School of Graduate Studies of the University of Ottawa in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Psychology. Ottawa, Canada ° December 1983
©
D a y id R ic h a r d
S ta p e lls,
OTTAWA, C a n a d a ,
1984.
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c ' U N I V E R S I T E D ' O T T A W A / U N I V E R S I T Y OF O T T A W A E c o le des Etudes s u p £ r ie u r e s / S c h o o l of G r a du a te S tu di es et de la r e c h e r c h e aS^d R e s e a r c h
NAME OF AUTHOR
STAPELLS,
--------- 41— TITLE OF THESIS
DEGREE
P h .D .
D a v id
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r --------------
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V
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>
STUDIES IN EVOKED POTENTIAL AUDIOMETRY
(P sy c h o lo g y )
1984
YEAR GRANTED
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STUDIES IN EVOKED POTENTIAL AUDIOMETRY , ' » STAPELLS, D a v i d R i c h a r d
Name of candidate < Degree
P h .D .
P sT e o f defence
Department January 1 8 ,
PSYCHOLOGY
1 9 8 4 ..- . ✓
k
.
Tim i Iicms jtrcjMrcit l i mh-i t h e s u p e r v i s i o n o f
T .W .
P ic to n
has been approved 6y a jury
c o m p o s e d o f th e f o l l o w i n g e x a m i n e r s :
.
K.
CAMPBELL
R.
GALAMBOS
K.
MARSHALL
D.
STU SS
A
-
.
A
-
(Dean of Graduatr Studies)
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©
Copyright by David Richard Stapells 1983
11
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ACKNOWLEDGEMENTS
J
I
would
unfailing
like
guidance
to
thank
Dr.
Terence
Picton
for
and encouragement over the past four
his
years.
His impatience to "Jcnow" was always a challenge, but his patience in the achieving of this goal I
would
made the process enjoyable. ■* ,• also like to thank Dr. Andr£e Durieux-Smith,
who
^provided the setting for' several of the studies completed in this thesis.
Her
advice
and
enthusiasm
for
these
studies
were
essential. Finally,
I gratefully acknowledge the financial support
of
4
the Natural Sciences and Engineering Research Council (NSERC) of * x Canada.
ill
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VITA
David the
Richard
Stapells was born February 11, 1955,
amidst
mountains and the sea in Vancouver, B.C., Canada*
-Om he _ graduated receiving
from
Simon Fraser University
in
In %. Burnaby,
1979, B.C.,
a Bachelor of Arts (Honours) degree in Psychology with
a minor in Kinesioldgy. *■
,
He of
Philosophy at the University of Ottawa in January, 1980.
research his
N. r “ V began work on the requirements for the degree of Doctor
supervisor was Terence W. Picton, MD, PhD.
postgraduate
studies
His’
Throughout
he wjis financially supported
by
the
Natural Sciences and Engineering Research Council 6f Canada.
THESIS AND PUBLICATIONS
Stapells, D.R. (1979). Effect of hyperventilation and breathhold on the brainstem evoked response. Unpublished Honours thesis. Department of Psychology, Simon Fraser University, Burnaby, B.C. Picton, T.W., Seguin, J.F., Hamel, G., Talajic, M., & Stapells, D.R'. (1981). Somatosensory potentials. Sensus, 1_, 9 - 20. Stapells, D.R. & Picton, T.W. (1981). Technical aspects-of brain stem evoked potential audiometry using tones'. Ear and Hearing, 2 , 20 - 29. Picton, T.W., Stapells, “D.R., & Campbell, K.B. (1981). Auditory evoked potentials from the human cochlea and brainstem. Journal of Otolaryngology Supplement, 9 , 1 - 4 1 . Stapells, D.R., Picton, T.W., & Smith, A.D. (1982). Normal hearing thresholds^for clicks. Journal'of the Acoustical "Society of America, 72, 75 - 79. Stapells, T.W., Picton, T.W., & Smith, A.D. The calibration of click intensity. Sensus (in press). •i iv
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Stapells, D.R., Suffield, J.B., & Picton, T.W. (1982). Effects of stimulus presentation rate on the middle-latency auditory evoked potentials. Journal of the Acoustical Society of America Supplement, 72, S54. (Abstract) Picton, T.W., Stapells, D.R., Perrault, N., Baribeau-Br&un, J. and Stuss, D.T. Human event related potentials. Current perspectives. In R.H. Nodar & C. Barber (Eds.), Evoked Potentials II. New York: Butterworth. (in press) Stapells, D.R., Linden, R.D., Suffield, J.B., Hamel, G.,’ & Picton, T.W. (1984). Human auditory steady state potentials. Ear and Hearing, (in press) Galambos, R., Kileny, P., Stapells, D.R., & Thornton, A.R.(1983). The 40-Hz Event Related Potential (ERP): Theory and • application. ASHA, 25, 154. (Abstract) Linden, R.D., Hamel, G..,, Stapells, D.R., & Picton, T.W. (1983). Human auditory steady state responses analyzed with Fourier analysis: The zoom technique. Journal of the Acoustical Society of America Supplement, 74, S65. (Abstract). Stapells, D.R., Per^z-Abalo, M., Read, D., & Picton, T.W. (1984). Frequency. specificity: Problems and solutions. In J.T. Jacobson (Ed.) The Auditory Brainstem Response. San Diego: College-Hill. (in press) ? Stapells, D.R., Picton, T.W., & Durleux-Smith, A. Estimation of threshold in normal and hearing-impaired individuals using *■auditory evoked potentials. In preparation.
V
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I
’■'sN
.ABSTRACT OF THE DISSERTAT: IV T J O j
N '.
Studies in Evoked Potential Audiometry..
David Richard Stapells
Doctor of Philosophy (Psychology) University of Ottawa, 1983
Four
sets' of- experiments were performed to evaluate
psychophysical behavioral
thresholds
to
brief
.the
and
how
these
thresholds may be estimated using the auditory evoked
potentials. The
stimuli
human
1
normal hearing thresholds for the clicks used to elicit
brainstem .auditory evoked potentials were evaluated, and the
effects " oh these thresholds of varying the polarity and symmetry of
the
click assessed. Threshold decreases 4.5 dB
change young
in
per
rate. The average threshold obtained from
40
tenfold normal
adults using 100-us square-wave clicks presented through a
TDH-49
earphone
equivalent
at
10/s was 36.4 dB peak SPL or 29.9
dB
peak
SPL. A root-mean-square measure of the pressure
over
the initial millisecond — measure
SPL(1ms) —
piovides a more consistent
of threshold with clicks of differing symmetry than
peak or peak equivalent measuresv
VI
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the
*
The
brainstem
vertex-positive Changes when
so
response
component.
The
morphology
that a vertex-negative component
high-pass 'filter
slopes
contain^ a large V__ of this response
to brief tones
are
used.
settings above 20 Hz
Tones
frequency-specificity,
becomes
with longer
and
prominent '
high
rolloff
rise-time^, have
greater
but rise-times longer than 5 ms result in
brainstem
responses
with 'smaller
amplitudes.
responses
to high-intensity -stimuli are not
The
brainsteA
frequency-specific,
and notched noise masking should be used. Stimulus
rates of 40-45/s result- in a 40-Hz 9 response which is about twice the amplitude of the 10
sinusoidal and
,
presentation
60/s responses. The 40/s response shows a linear decrease in
amplitude
and
intensity
is
recordable
to
High-frequency Signal
a
linear
functions.
in
latency
when
decreased from 90 to 20 dB nHL. This within stimuli
averaging
amplitude/rate,
increase
a
few
dB
resylt
in
of
stimulus
response
behavioral
threshold.
lower-amplitude• responses.
and Fourier analysis provide nearly
. amplitude/intensity,
Fourier
analysis,
is
and
identical
latency/intensity
however, may be
the
faster
and
evaluated
for
t
less-expensive method. Eight
evoked
frequency-specific
potential
techniques
objective audiometry
were
at 500, 1000, 2000, and
\
4000 tests
Hz
in normal-hearing
were
Response
Slow Response, the Transient
(MLR), the
brainstem Notched
the
response
and hearing-impaired
40-Hz
Steady State
techniques
(Derived
subjects. Middle
Potential, Responses,
The
Latency and
Clicks
Noise, unmasked Tone responses, Tones in Notched vii
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five in
Noise,
and^rones in White Noise).
The high noise intensities- required
to mask clicks may result in small and variable responses and may cause
temporary threshold shifts. The ABR/Derived Responses
ABR/Clicks useful
in Notched Noise tests do not therefore,appear to
variable
not
appear to be useful for EP audiometry.
and
be
for EP audiometry. The Transient Middle Latency Responses
are
that
and
the
and thresholds are difficult'to-'de^ermine and
The results indicate
auditory brainstem responses to tonal stimuli
unmasked) are the best for audiometry.
thresholds thresholds. prediction
were
within
Noise in
the
4 - 6
masking
of
presence
of
(masked
On average, response
'dB
of
the
tones
steep
do
pure
tone
behavioral
improves
high-frequency
losses.
viii
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threshold hearing
TABLE OF CONTENTS page ACKNOWLEDGEMENTS .................................... iii VITA AND PUBLICATIONS ............................
. iv
ABSTRACT OF THE DISSERTATION.........................
vi
INTRODUCTION .......................................
1
PAPER I. NORMAL HEARING THRESHOLDS FOR CLICKS .......
4
ABSTRACT ......................................
5
INTRODUCTION ..................................
6
METHODS .......................................
9
A*
Subjects
............................
9
B • Stimuli ..............................
9
C . Experimental procedure ................
11
D.
12
Data analysis......
V RESULTS .......................................
13
A. Experiment 1: Normal thresholds for 100-us clicks ...................
13
B. Experiment 2: The rate of stimulus presentation .............
13
C. Experiment 3: Duration of listening period...................
14
D. Experiment 4: Click symmetry ..........
14
DISCUSSION.......
16
FOOTNOTES ........................ ............
22
ACKNOWLEDGEMENTS ..............................
23
TABLES .......................................
24
ix
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I
REFERENCES ....................................
27
FIGURE LEGENDS ................................
31
FIGURES ................................. '.....
32
PAPER II. TECHNICAL ASPECTS OF BRAINSTEM EVOKED POTENTIAL AUDIOMETRY USING TONES ..........
38
ACKNOWLEDGEMENTS ..............................
39
ABSTRACT ......................................
40
INTRODUCTION ..................................
41
METHODOLOGY ............................
44
RESULTS AND DISCUSSION .........................
47
Experiment 1: High-pass filter settings ....
47
Experiment 2: Stimulus presentation rate ....
50
Experiment 3: Location of the reference electrode ...................
52
Experiment 4: Intensity effects .••••••.....
53
Experiment 5: Stimulus rise-times .........
56
Experiment 6: The effects of notched noise ..
59
CONCLUSIONS ...................................
62
REFERENCES ....................................
64
FIGURE LEGENDS ................................
69
FIGURES .................................
74
PAPER III. HUMAN AUDITORY STEADY STATE POTENTIALS ....
85
ACKNOWLEDGEMENTS ..............................
86
ABSTRACT ......................................
87
INTRODUCTION ..................................
88
GENERAL METHODS .......
91
Subjects ................................. X.
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91
I
Stimulus generation .......................
91
EGG recording^S^fcedures ......... ........
92
...... .
93
RESULTS AND DISCUSSION ........................
95
Response analysis
Experiment
1: Stimulus presentationrate ...» 95
Experiment
2: Fourier analysis andaveraging*
97
Experiment
3: Stimulus intensity .........
99
Experiment
4: The zoom technique .........
101
CONCLUSIONS .....
105
REFERENCES .................................... 109 TABLE 1 ....................................... 113 FIGURE LEGENDS ................................ 114 FIGURES ...................................... C, PAPER IV. ESTIMATION OF THRESHOLD IN NORMAL AND
119
I ■
HEARING-IMPAIRED INDIVIDUALS USING AUDITORY EVOKED POTENTIALS •,....................... 132 ACKNOWLEDGEMENTS ..............................
133
ABSTRACT ...................................... 134 INTRODUCTION .................................. 136 Slow Responses ...........................
137
Middle Latency Response ................... 139 Auditory Brainstem Response ...............
142
The 40-Hz Response
149
Summary .................................. 151 M ETHOD ....................................... Subjects
..........................
152 152
Stimuli .................................. 154 xi
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EP recordings ..............
159
Experimental procedures ........
160
Data analysis:Response criteria ............ 162 Evoked potential measurements. 164 Statistical analyses .......
166
RESULTS ......................................
167
(A) Normal subjects:
~
ABR/Derived Responses ........... . 167 ABR/Clicks in notched noise........ 168 ABR/Tones (masked and unmasked)..... 169 i• Transient MLR (10/s) . 171 The 40-Hz steady state potential.... 171 Slow Responses
........
172
(B) Hearing-Impaired subjects .............
173
(C) Test evaluation.....
181
(i)
Test accuracy ..............
181
(ii) Inter-subject consistency .... 184 (iii) Response clarity
....... 185-
(iv) Inter-rater reliability .....
186
(v)
186
Combined results ...........
DISCUSSION ..
187
(A) Normative d a t a ........................ 187 Effects of stimulus intensity
...... 188
Effects of stimulus frequency
...... 188
Effects of stimulus masking .......
189
(B) Audiometric usefulness ................
191
Tests with poor scores ...........
192
xii
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I
Tests withintermediate scores ..... 195 Tests with
bestscores .............197
(C) General comments ..............
199
(D) Recommendations ...............
• 201
REFERENCES ..................................... 203 TABLES .........................................220 FIGURE LEGENDS ................................ 230 FIGURES ........................................250
\ S.
Cj
xiii
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I
1
^
U
'
;
INTRODUCTION
I This
thesis
consists of four papers, each representing
attempt to provide some answers to questions in audiometry.
The
format
an
evoked potential
of each paper is that required
by
the
journal in which it has been (or will be) published. The first paper investigates a topic which is fundamental to —
the recording of auditory '
and
physical
audiometry. of America, clicks,
calibration
of the acoustic stimuli
Published in the
used
in
this paper provides a normal reference threshold for
stimuli.- The studies in this paper also lay
groundwork
EP
Journal of the Acoustical Society
and compares techniques for the physical calibration
acoustic
for
evoked potentials (EP): the behavioral
for
the calibration of normal behavioral
down
of the
thresholds
tonal stimuli. These thresholds are presented in the
fourth
paper. The
goal of the second paper, published in Ear and Hearing,
was to determine the optimal stimulation and recording techniques for this and
brainstem.EP audiometry using tonal stimuli. In
particular,
paper demonstrates the effects of amplifier filter settings rolloff slopes, stimulus frequency, stimulus rise-time,
notched
noise masking on these responses.
experiments
The results of
and these
are summarized as a set of recommendations for using
this technique. The
third
paper,
to
be
published
in
Ear and Hearing,
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I 2
summarizes experiments investigating the recently-described 40-Hz Steady State Potential. Recent response
might
studies suggested that this "new"
prove to be very useful for EP audiometry.
The
results of the studies presented in this paper indicate that this steady
state
potential
I
audiometry.
does
Furthermore,
show
the
promise
results
of
for this
objective
paper
also
indicate that the use of the frequency-based technique of Fourier analysis more
to
record the 40-Hz response may
quickly,
more
objectively,
and
provide
less
information
expensively
than
paper of this thesis presents the results
of . a
conventional signal averaging techniques. The study
final
which evaluates the usefulness of
frequency-specific determine optimal
objective-
eight EP techniques for
audiometry.
The objective was
the best test. Each technique was evaluated using stimulus and recording protocols to provide
to the
information
within a specified time. All techniques were evaluated in each of ten normal-hearing and ten. hearing-impaired subjects. The results presented from
in this"V>aper clearly delineate the poor EP techniques
the better techniques, and demonstrate their strengths
weaknesses. j,,
recommendations
for the practice of evoked potential audiometry. The
*:
The paper concludes with a set of
and
four
papers
to answer some of the potential
in
thesis
represent
an
attempt
technical and practical problems of evoked
audiometry.
providing, an
this
accurate
audiometric information
They
are united by the overall
and efficient
technique
for
goal
of
obtaining
as early as possible in a child's life.
-a
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-
StapelIs e t a l .
Page
4
J . Acoust. Soc. Amer.
NORMAL HEARING THRESHOLDS FOR CLICKS
David R. S t a p e ll s
_
;-f
School of Psychology, University of Ottawa, 651 Cumberland, Ottawa Canada
KIN 6N5
I Terence W. Picton
Department of Medicine, University of Ottawa, Ottawa General Hospital 501 Smyth Road, Ottawa, Cartada r K1H 8L6
Andr§e D. -Smith,Department of Audiology, Chi 1dren1s"Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Canada
K1H 8L1
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/
Stapells et a l .
Page
J. Acoust. Soc. Amer.
ABSTRACT This
paper
evaluates the normal hearing
thresholds fo r c l i c k s
and as se ss e s the e f f e c t s on these thresholds of varying the duration of the l i s t e n i n g period and the pr e se n t ati on - ra te , of the c l i c k s . \
There were no
po la r it y
and symmetry
s i g n i f i c a n t changes in threshold a s t h e
\
l is t e n i n g - p e r i o d decreased from 2 s to 300 ms.
There was,
however, a
2 .5 dBNincrease in threshold as the li s t e n i n g - p e r i o d decreased from 300
\
t o 100 ms., creased
Increasing stimulus pre se nt atio n- ra te from
threshold 4 .5 dB per tenf old change in
s i g n i f i c a n t d if f e r e n c e s tion (
i'—
adults
The average \
using
100 ; js
\
ra te .
to 80/s de
There
were no
in threshold between rarefa ction and condensa-
\
clicks.
5
threshold
square-wave
obtained from 40 normal
clicks
presented
young
through a TDH-49
\ earphone at 10/s was 3 6 . 4 peak SPL or 29.9 Neither peak SPL-nor peak equivalent thresholds f o r c l i c k s \
mean-square - SPL(lms)
measure
with of
the
dB peak equivalent
SPL measurements
different
\ pressure
-
degrees over
of
SPL.
gave c o n s is t en t
symmetry.
the i n i t i a l
A root-
millisec ond
gave a threshold of 2 5 . 6 \ d B . This SPL(lms) measure of \ threshold proved to be far more c o n s is t e n t "for c l i c k s with d i f f e r e n t \
degrees of symmetry than e i t h e r the peak SPL or the peak equivalent SPL measures. \ PACS numbers: 43.66.C, 4 3 .6 6. S , 43.63.R
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5
S t a p e l l s et a l .
Page
6
J. Acoust. Soc. Amer.
INTRODUCTION Brainstem auditory
evoked
A po t en ti a ls are e x t e n s iv e ly used
to
eva luate human auditory and neurological function (Jerger e t a l . , 1980; Stockard
et
a l . , 1980; Glasscock
et
a l . , 1981; Rowe,
la bo r ato r ie s use broad-band c l i c k s generated by (10-250 ,us) standard
Most
passing short-duration
e l e c t r i c a l pulses through an earphone.
technique for
1981).
c a lib r atin g the i n t e n s i t y
There i s as y e t no of
these
stimuli.
Both behavioral and acoustical c a li b r a ti o n s are presently employed. There are two methods of obtaining intensity.
a behavioral
c a li b r a t io n of
In the f i r s t method stimulus i n t e n s i t y i s measured r e l a t i v e
t o the behavioral ("sensation level" cannot be used as
threshold
of
or SL).
the p a r tic ul ar
This i s
subject
an important
a standard because
it
%
will
being te s ted
measurement but i t
vary with
the ambient
n o i s e , the abj^ity of the subject to respond a c cu ra te ly , and the degree ■s
of
hearing
loss.
Most
labora tor ies
there for e
obtain
the average
threshold o f ten normally-hearing
young adults (Picton et a l . ,
This second
c a li b r a t io n gives
level"
method of behavioral
or nHL reference.
This
thresholds ("hearing level" 1969)
but
duration,
is
specific
is
or HL)
1977).
a "normal hearing
s im ila r to the standard reference fo r pure
to the stimulus and
frequency-spectra and rate of
tones (ISO,
1'964; ANSI,
to the laboratory.
presentation
of
w i l l vary among la b o r a to r ie s.
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The
the stimuli
is c l i c k s of
different
polarities
when presented binaurally at
rates
from
20 to
102/s. t
Increasing the rate of decreased the threshold
stimulus presentation
lev el
by
about
5
from
dB. Perceptual
5 / s to 80/s processes
i n t e g r a t e acoustic energy over several hundred m il lisec ond s (Zwis\ocki, 1969; Pedersen and Salomon, stimuli are s im il a r
1977).
presented probably
manner
to
increasing
Increasing the rate at which b r ie f
invokes the
t h i s temporal summation
duration
of
a continuous
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in a sound
St a p e ll s et a l .
Page
17
J . Acoust. Soc. Amer.
(Zwicker,
1975).
There are,
however,
some d if f e r e n c e s
summation processes for the two types of s t i m u l i .
between the
Experiment 2 demon
strated a smaller summation e f f e c t (4 .5 dB per te nf ol d increase in rate per second) f o r c l i c k s than has been reported f o r continuous pure tones (8-10 dB p e r ,te n fo ld inc r ea se in duration). tonal
stimuli have reported e f f e c t s of stimulus presentation rate that
are si mi lar to the present study a l.,
Other s tu d ie s using br ie f
(Zerlin and Naunton,
1979; Yost and Klein, 1979).
The smaller summation e f f e c t may be
relat ed to the wide frequency-content of b r i e f s t i m u l i , and Garner
(1947)
f o r broad-band
having
1975; Picton e t
Zwicker (1975)
reported smaller temporal summation e f f e c t s
stimuli.
The actual
high-frequency
content
of
the
stimulus may also play a part since there i s l e s s temporal summation at higher frequencies
fo r pure
tones (Watson and Gengel,
1969; Pedersen
and Salomon, 1977; ..Chung, 1981) and f o r th ird -o ct av e c l i c k s (Zerlin and 1 Naunton, 1975). Zwislocki (1960, Figure 9) reported a 10 dB summation e f f e c t per te n f o ld change in Flanagan (1961),
It
is
rate of
0.5 ms c l i c k s .
on the other hand, reported very l i t t l e change in the
threshold fo r 100 |is c l i c k s 102/s.
the presentation
presented at
rates
increasing frOT20J>o
po s s ib le that these d if f e r e n c e s
may be related to the
d i f f e r e n t frequency spectra of the d i f f e r e n t s t i m u l i ,
the 500)
jjs
pulse
as
the
of Zwislocki containing r e l a t i v e l y more low-frequency energy: We
observed
a
2.5
dB
decrease
in
threshold
l i s t e n i n g - p e r i o d was increased from 100 ms to 300 ms.
This
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indicates^
Stapells et a l .
Page
18
J. Acoust. Soc. Amer.
a the
temporal
summation
period
200
period
reported
1,975).
ms
The data
shown in
2.0 ms.
by
our
p lo tt e d by Zwislocki (1960, of 0 .2 -
within
these
comparable
to
others (Zwislocki, 1969; Zwicker,
Figure 5
Figure 7)
Both s e t s
lim its,
are
qui te si m il a r to those
f o r 100/s c l i c k s with durations
of data show a decrease
in threshold of
about 5 dB as the l i s t e n i n g duration increased f \ slopes. Again there was ai^ interaction
I R e p ro d u c e d with perm ission of the copyright owner. Further reproduction prohibited without permission.
S ta p e lls and P ic to n B ra in s te m re s p o n s e s to to n e s
between the two effects such that the effect of rolloff slope was not
significant
differences less
at
in
70
at 10 Hz and increased from 20 to 70
dB as compared to 110 dB but the
7 where,
plotted. same V*
The
were
much
differences
were
amplitude related to filter settings
still -significant at 70 dB. Figure
Hz.
for
The amplitude effects are shown
clarity, only the
results
at
in
35/s
are
The morphology of the V-V* complex changed in much the
manner
at 90 and 70 dB as at 110 dB in Experiment 1.
The
component was most prominent at filter settings of^40 and
70
Hz. The
effects
of changing the rate of stimulus
were
similar to those obtained in experiment 2.
rate
of
There low a
presentation
Increasing
tone presentation caused an increased.wave 'V
the
latency.
was no effect on V' latency except that the combination of intensity, high filter setting and high rolloff slope caused
decrease
rate.
in V' latency with increasing stimulus
There
amplitude
was
no
effect of increasing
The
on
the
V-V*
except at high filter settings and low Intensity where
the amplitude were smaller at 35/s rates. j
rate
presentation
results
»
of this experiment show quite clearly that
at
all intensities larger brainstem responses are recorded using the lower
high-pass filter settings and rolloff slopes.
settings and
20
The optimal
appear to be 10 Hz at either 6 or 24 dB/octave Hz
at 6 dB/octave rolloff.
The recognizability
rolloff of
an
average waveform, however, depends upon both the amplitude of the response
and
the amount of
background
noise remaining after averaging.
electroencephalographic
It is possible, therefore, that
j
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56
S ta p e lls and P ic to n B ra in s te m r e s p o n s e s t o
higher
filter
assitance noise
certain clinical conditions where in
the
who • are
activity* filter
settings and/or higher rolloff -slopes may
in
level
patients
to n e s
The
will
10-40 Hz range is high -
sedated
use
or who have high
of
response. it
is
of
background
for
example
levels
of these higher settings on
of
the
in
muscle
high-pass
alter the brainstem response morphology to
prominent vertex-negative V' component. effects
the
be
give
a
There were no consistent
stimulus presentation rate on the amplitude
of
the
Because of the decreased timp necessary for averaging,
therefore
preferable
to
use
the
faster
stimulus
presentation rates.
< Experiment 5 - Stimulus Rise-times This experiment evaluated the effect of different rise-times on
the
Tones t
; *
,
brainstem
with
response to tones of. different
rise-times
of
1,
2, 5 and
8
ms
frequencies.
and
equivalent
fall-times
were presented at frequencies of 500, 1000, 2000 and t « 4000 Hz and aj i an intensity of 100 dB peak SPL at a rate of 35/s. t
>
Averaging was carried out over 2000 trials using a sweep duration of 25.6 mj/ . The subjects
X
average are
wave
plotted
V in
latencies and Figure
8.
amplitudes
There
were
for
eight
significant
increases in V latency with decreasing stimulus freuency and with increasing
rise-time.
There
was also an
interaction
between
\
these
two
increasing
effects ^euch rise-time
was
that
the
greater
increase in' latency at
the
lower
with
frequencies.
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S ta p e lls and P ic to n B ra in s te m re s p o n s e s t o
Regression each
frequency.
latency lines Hz.
lines
of
to n e s
were calculated for the rise-time
effects
The equation for these regression
lines
wavfe V= a (rise-time) + b.
The slopes (a) of
at
was: these
were 0.44, 0.40, 0.30 and 0.26 at 500, 1000, 2000 and 4000 The respective latency intercepts (b) were 6.88, 6.48, 6.33-
and 6.11 ms. ............... Insert Figure 8 about here.................... v.. These results show a definitely increasing effect of rise-time
on
explanation acoustic
V latency at the lower frequencies.
for
this
could
be the
increased
One spread
of . the
energy in the spectra of low-frequency tones with short
rise-times.
These rapid-onset tones could thus evoke
i through more
basal regions o£ the cochlea than the
longer rise-times. dB
possible
tones
tones
with
The regression line calculated for 500 Hz 100
presented in notched noise.(data from
however,
responses
Experiment
6),
showed a slope of 0.49 as well as a generally increased
latency with a latency intercept of 8.65 ms.
The regression line
for the 2000 Hz 100 dB tones in notched noise had a slope of 0.23 and
an
intercept
of
7.12 ms.
It
therefore
seems
that
the
alteration in slope with stimulus frequency is a true function of
J
stimulus frequency and not an artifact of acoustic distortion. Several latency
researchers
with
Brinkmann and V.' trigger time" rise-time connecting
of to
increasing Scherg which the
have
reported an increase in
stimulus
rise-time (3,
(3) introduced the appears
6,
concept
to represent
the
q^imulus when the majority
of
the brainstem response generator
wave 13,
of
17).
"virtual
point nerve are
V
on
the
fibers
activated.
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I Stapells and Picton Brainstem responses to tonAs 0
58 .*>
This virtual trigger time is a function of both the rise-time and the
intensity of the stimulus.
also
Our results indicate that it
a funotic^n of stimulus frequency.
where
there
phase, major This
is
nerve
the
fiber
delay
At the lower frequenies,
locking of nerve fiber activation
increasing
would
rise-time
could
delay
activation by one or more be
greater
is
to
stimulus
the
time
of
stimulus cycles.
the lower thefrequencyof
the
stimulus. The
V-V'
significant These was
amplitude
of
the
brainstem
response' showed
changes with both stimulus frequency and rise-times.
effects are shown on the right of Figure 8. greater
increasing
at
the
lower
rise-time.
frequencies
The major change)^Ln
and
The amplitude decreased
amplitude
with
occurred f
between the rise-times of 5 and 8 ms. The
effect of stimulus rise-time on the brainstem response
amplitudi^ appears "" stimuli. does
not
cause
a
tones.
than
2.5 ms.
amplitude
impulses
whitenoise
any definite change in the
(3, 13).
with
in
differ between
and
tonal
) Varyingythe rise-time of white noise bursts up to 10 ms
amplitude indicate
to
to
brainstem
response
Our results and those of Kodera et al
definite decrease in amplitude at longer
(17)
rise-times
This is particularly true at rise-times of
greater
At shorter rise-times there maynot be any
change
(6).
nerve
It is possible that the
locking
the phase of low-frequency stimuli may
of cause
more
jitter at longer rise-times in tonal as opposed to noise stimuli. This jitter would result in broader responses of lower amplitude. Our results indicate that for tonal stimuli rise-times of 5 ms or
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S ta p e 1 1 s an d P ic to n B ra in s te m re s p o n s e s t o
shorter
would
be
to n e s
preferable
since at
longer
rise-times
the
brainstem response is quite attenuated.
Experiment 6 - The Effects of Notched Noise ' / This experiment was designed to investigate * frequency-specificity of the brainstem responses to tones different rise-times. intensities mixed
with
Tones of 500 and 2000 Hz were presented at
120, 100, 80 and 70 dB peak SPL either alone
or
with notched noise (with the rejected band centered on the
frequency was
of
the
25
of the tone). dB
The noise intensity measured in RMS SPL
less than the tone intensity measured in
peak
SPL.
Stimuli were presented at 35/s and averaging was carried out over 2000 80
trials with a sweep duration of 25.6 ms. and 70 dB were replicated.
was
The responses
at
The rationale for this experiment
that if the notched noise caused the response to change, the
response to the tone alone was in part mediated by frequencies in f* the tone away from its nominal frequency. ) The quite in
effect
complex.
Figure
9.
significantly
of the notched noise on the wave V latency
was
The average data from eight subjects are plotted The latency of wave V in the 500 Hz response
was
increased by- notched noise at all intensities
for
the 1 ms rise-times, at 100 dB or more for 2 ms, at 80 dB or more > for 5 ms, and at 100 dB or more for 8 ms. The latency of the 2000 HS response was significantly increased by the notched noise at for
80
dB or more for the 1 ms rise-time, and at 100 dB or
more
2 ms. There were no significant effects of the notched ntfise v_
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S ta p e lls and P ic to n B ra in s te m re s p o n s e s to
to n e s
on the 2000 Hz response latency for rise-times of 5 or 8 ms. .....
Insert Figure 9 about here...... .........
The notched noise significantlyXreduced the amplitude of the brainstem the
response.
higher
This reduction ih amplitude was greater
at
intensities and at the los^uf-jise-times. At 500
Hz
there
were
noise
at 80 dB or more for the 1 and 2 ms rise-times, at 100
or V-V*
more
significant amplitude differences with
for the 5 and 8 ms rise-times.
amplitude
for
the
At 120 dB
the
5 ms rise-time tones was 1.20 pV
tones were alone and 0.87 pV when in notched noise. amplitudes
were
significant for
all
0.42
rise-times
At
2000
average
when
the
At 70 dB the were
differences in the V-V' amplitude at 100 dB or
more
was
0.32 pV.
dB
there
rise-times.
and
notched
Hz
At 120 dB the average amplitude for. 5
1.16 pV when the tones were presented alone
0.56 pV when in notched noise.
ms and
At 70 dB the amplitudes were 0.37
and 0.36 pV. Two
possible explanations for the effects of notched
noise
t
can be considered. the
effective
The first is that the masking noise decreases
intensity
of the tone',
thereby
decreasing
the
amplitude and increasing the latency of the response.
The second
is
particular
that
the notched noise limits the response £o
a
area of the cochlea, masking out those parts of the response that are
mediated
the
spread
dynamics
of
through other regions of the cochlea activated
of
acoustic
the
energy in the brief
travelling
wave.
The
tone
first
or
by
explanation
probably not a major cause of the experimental findings.
by the is
It does
9
not
explain
the different effects of the masking noise
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at
the
s
S ta p e lls and P ie to n B ra in s te m r e s p o n s e s to
different
61 to n e s
frequencies
Furthermore,
increasing
9
or ' at
the
different
intensities.
the intensity of the masking noise
has
little
effect on the amplitude or latency of the 500 Hz response
(23).
The second line of explanation can account reasonably well
for
all
evident
of
the
observations.
The latency
changes
are
at 500 Hz because the 500 Hz response latency is
determined activated
by
thp
sharp-peaked
frequency
mainly
of the cochlea * by the spread of frequencies in the brief tone. These
high-frequency
higher
most
regions
regions are more readily synchronized and give component
latency.
The
frequency
region
in
the
response
that
determines
notched noise masks the response from the
the
higher
leaving a braod, longer latency response
from
the
500 Hz region of the cochlea.
has
less
effect because of the higher frequency-specificity
the
2000
Hz
cannot
the .cochlea. A because the of
noise of
thev response ^ shift far to an earlier or more synchronizable region of
*
stimulus (cf
At 2000 Hz the notched
a
Figure 1) and because
The amplitude changes occur at
both
frequencies
of the masking of the response to frequencies outside of
rejection band of the notched noise.
The decreasing effects
notched noise at lower intensities occur because at the lower
intensities
the
skirts
of the tone frequency
spectrum
become
subthreshold. If
we
correct,
therefore accept the second line of
explanation
as
then the results of this sixth experiment indicate that
the brainstem response to brief tones at intensities of 100 dB or more is not frequency-specific regardless of the rise-time of the tone.
At rise-times of 1 or 2 ms the response to 500 Hz tones is
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62
S ta p e lls and P ic to n B ra in s te m re s p o n s e s t o
to n e s
S' not even frequency-specific at lower intensities. :
j
CONCLUSIONS
The recorded low
J
largest brainstem responses to low frequency tones
are
using
and
rolloff
low high-pass filter settings (10 or 20 Hz)
slopes.
vertex-positive
Under
wave
these
is recorded.
conditions At higher
a
large
high-pass
clear filter
settings, particularly if higher rolloff slopes (24-48 dB/oct&ve) are
used, the response is smaller and tends to show a
prominent
vertex-negative wave. There response rolloff
are
no significant changes in the amplitude
recorded
using low high-pass filter settings
of
the
and
low
slopes when stimulus presentation rate of up to 35/s are
used.
There is, however, a significant increase in the
latency
of wave V at the higher presentation rates. Postauricular tones
and
mid-mastoid
muscle reflexes are evoked by high
intensity
can distort the brainstem response recorded reference electrode.
using
a
A reference located lower down
on
the mastoid is therefore preferable.
If the wave I recording
is
not essential, the reference electrode can be located on
the
lower part of the neck. Tones specificity. smaller occur
with
longer
They
amplitudes. with
elicit
rise-times
have
responses with
greater longer
acoustic
latency
and
Xn general, latency increases of 0.2-0.5 ms
increases
of
1
ms
in
rise-time.
The' exact
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S ta p e lls and P ic to n B ra in s te m r e s p o n s e s t o
63 to n e s
^ Stillman, R.D., G. Moushegian, and A.L. Rupert. 1976. Early tone-evoked subjects.
27.
67
responses
in normal and
hearing-impaired
Audiology 15, 10-22.
Suzuki, T., Y. Hirdi, and K.'Horiuchi. 1977. Auditory brain stejn responses to pure tone stimuli. Scand. Audiol. 6, .51-56.
28.
Suzuki,
t
T.,
filter v
and K. Horiuchi. 1979. Effect ah
on
-
Paper presented
Auditory
high-pass
the auditory brain stem responses to •
~pips.
of
Responses
at the
from, the
US-Japan Brain
tone
Seminar
on
Stem, 'Honolulu,
Hawaii. • ‘29.-
Terkildsen,
K., P. Osterhammel. 1981. The
reference /Wl
30.
eletcbrode ° position
recordings
Terkildsen,
K.,
P. Osterhammel, and F.
Far-field
positions. Scand.
Huis
the
Veld.
electrode
Audiol. 3, 123-129.
Terkildsen, K., P. Osterhammel, an^F.-Huis in't Veld. 1975. '
32.
in't
electrocochleogrpphy,
it
*
Far-field electrocochleography. Frequency *
of
of
audito auditory brainstem responses. Ear and Hearing 2, 9-14.
1974.
31.
on
influence
specificity
of the response. S^and. Audiol.-4, 167-172. Weber, B.A. and R.C. FolsdSu^ Brainstem wave V latencies to tone' pip stimuli. .. J. Am. AiA. Aud. Soc., 2, 182-184.
33.
Wood,
* ' ? i
•
M./M.R. Seitz, and J.T. Jacobson.
• ■
1979.
Brainstem
’ •
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J
. S ta p e lls and P ic to n . B ra in s te m re s p o n s e s t o
to n e s
.
^
electrical responses from selected tone pip stimuli* J* Am. 34.
Yamada,
Aud. Soc. 5, 156-162. 0.,T. Yagi, H. Yamane,
Clinical v\
and J.-I.
Suzuki.
1975.
evaluation of the auditory evoked brain
stem
response. Aurix Nasus Larynx 2, 97t -105. 35.Yoshie, N ., and T. Okudaira. responses 252,
1969. Myogenic evoked potential
to clicks in man.
Acta Otolaryngol.
89-103. '
%
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Suppl.
2e ?
S ta p e lls and P ic to n B ra in s te m re s p o n s e s t o
69 to n e s
f i g u r e legends
Figure 1 acoustic by
the
The effect of different rise and fall times
on
the
spectra of 590 and 2000 Hz tones. Tones were generated TN-3000
equivalent
system
fall
with rise-times of 1, 2, 5
and
times, and plateau durations of 0.01
8
ms.
ras, The
tones were presented through a TDH-49 earphone at an intensity of .115 and
I The acoustic signal was recorded using a Bruel
dB peak SPL.
Kjaer microphone and analyzed using a
TN-1500 sfgnal analyzer. each
laboratory-programmed
The power spectral density function for
tone isj^lotted between 100 and 10,1)00 Hz using logarithmic
' intensity
arid-frequency axes.
The intensity axes are
arbitrary
(0 dB is approximately 40 dB SPL). „
Figure 2 the at
- The effects of different high-pass filter settings on
brainstem response to 110 dB peak SPL 500 Hz tones presented a
rate
of 10/s.
Recordings were taken between
vertex
and
mid-mastoid electrodes and each tracing represents the average of 2000 responses.
Relative negativity at the vertex is represented *
f
by
an upward deflection. ^The vertex-positive wave V,
by
the open triangles, is most prominent at the lowest
of^ the
high-pass
indicated
by
filter.
The
vertex-negative
V'
indicated settings component,
the filled triangle, is particularly prominent
at
the 40 Hz 24 dB/octave filter setting. p Subject D.S. c % Figurp 3 rolloff
J*
- The effects of changing high-pass filter settings and slopes
on the brainstem response to 500 Hz tones.
\
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The
I 70
S ta p e lls and P ic to n B ra in s te m r e s p o n s e s t o
to n e s
average
data
wave
is shown on the left and of wave V' on the
V
from eight subjects are plotted.
The
latency
of
right.
The
V-V' amplitude is plotted in the center.
Figure 4
-
high-pass tones*
The
effects
filter
of
settings
stimulus
presentation
rate
on the brinstem response to
The duration of the averaging sweep was 50 ms.
and
500 At
Hz 35/s
the
interstimulus time (28.6 ms)‘is less than
and
therefore a second response is initiated prior to the end of
the
sweep.
lines.
As
This
is illustrated in the figure
the
the
dotted
well, this second response has been superimposed
the first in the initial portion of the tracing. (S.S.)
by
on
In this subject
increase in stimulus presentation’ rate from 20/s
to
35/s causes a decrease in the amplitude of wave V (open triangle) ,and
an increase in the amplitude of V' (filled triangle).
This
is probably because of the superimposition of these components on the negative *wave occurring at 40-45 ms after the preceding tone. When
the
high-pass filter setting is changed, the V'
component
has a shorter latency and small amplitude. V
*
Figure 5
- JJostauricular
recorded
to yo, 90 and 70 dB peak SPL 500 Hz tones presented at
a
rate
vertex
of 10/s. to
reflexes.
low-mastoid electrodes, and the recordings
High-pass
filtering slope.
Responses
The dotted tracings represent recordings
represent
rolloff
muscle
from
vertex
to
continuous
mid-mastoid
was performed at 10 Hz with a
Each
tracing represents the
were
from
tracings
electrodes. 6
dB/octave
average
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of
2000
%
V
Stapells and Picton Brainstem responses to tones
responses upward large
and
negativity
deflection. muscle
disappeared
by
an
AT 110 dB this subject (P.F.) exhibited
a
reflex at
71
at the vertex is
represented
that decreased in amplitude at 90
70\dB.
dB
and
The muscle reflex was very focal in
its
scalp
distribution Wind did not show up in the
using
the
brainstem location began
low-mAstoj.d
electrode.
The
V
recordings component
made
of
response
the
of the reference electrode.
before
the
the
peak
of
the k
However, the muscle reflex
V*
wave
and
distorted
any
measurement of this component.
Figure 6
- The effects of high-pass filter settings and stimulus
presentation rate on the response to 500 Hz tones. in
this
figure
responses
from
each represent the average of subject
S.S.,
obtained
The waveforms
4000
using
a
individual vertex
to
low-mastoid derivation and a high-pass filter rolloff slope of 24 •% dB/octave. With decreasing intensity wave V (open triangles) showed
increasing latency and decreasing amplitude. The f vertex-negative V' component (filled triangles) is best seen at
J
the 40 and 70 Hz filter settings.
With decreasing intensity this
V' wave also increased in latency andjdecreased in amplitude.
Figure 7 - The effects of high-pass filtering on the amplitude of “ '“ « the
brainstem response to 500 Hz tones of different intensities.
The
average
tone figure
V-V* amplitude d^ta from 8 subjects is
intensities of 110, 90 and 70 dB peak SPL. only
the
35/s
data
from
Experiment
plotted
at
To simplify the 4
are
30
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plotttjed.
Stapells and Picton Brainstem responses to tones
Increasing decreased smaller
the
filter
amplitude
72
setting or the rolloff
qf the brainstem response*
slope
causes
This effect
a is
but still significant at the lower intensities. ^At each
intensity the largest wave V amplitudes are recorded using the 10 Hz
filter settings with either the 6 or 24 dB/octave rolloff
or
using the 20 Hz setting with the 6 dB rolloff.
Figure 8 - The latency and amplitude of the brainstem response to tones
of
different frequencies and rise-times.
The
tones
had
rise-times of 1, 2, 5 and 8 ms, plateau durations of 0.01 ms, and fall-times- equal intensity data
to the.rise-times.
They were presented at
of 100 dB peak SPL and at a rate of 35/s.
from eight subjects are plotted in this figure.
latency
is
plotted
an
Thtf- average The. wave V
on the left and the V-V' amplitude
on
the
effect of notched noise on the latency
of
the
right.
Figure 9
-
brainstem
The
response
to tones. ’ Tones of 500 Hz and 2000 JJz were
presented
at 35/s either alone (continuous lines) or in notched I ** (dotted lines) at 25 dB'below the tone intensity. The
noise average
latencies
of wave V for eight subjects are plotted
tone rise-times of 1, 2, 5 and 8 ms. /
causes
a
for
At 500 Hz the notched noise
prolongation in the latency of the response.
This
is
signifif^tiie averaged evoked potential was measured average of the peak-to-peak amplitudes in the’ waveform, number
and
location
of
these
determined
using
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a
A u d ito ry s te a d y S ta p e lls e t a l .
sinusoidal
s ta te p o te n tia ls
94 >
template
of
the
same
frequency
repetition. in
as
the
rate
of
H
*
The latency to the first major vertex-positive peak
the averaged 40-Hz waveform was recorded. At higher rates
of
stimulus presentation, howeverv^one cannot actually associate any individual "derived was
response
cycle with a particular stimulus cycle.
latency" of^the averaged steady state evoked potentials
therefore 'obtained
(5,6).
A
using the method
proposed
by
Diamond
each subject,, linear regressions were performed on ¥ latency/ISI plots for the prominent positive and negative
the peaks
For
of
latency
the
response between 35/s and 55/s, and
intercept
taken as the derived latency.
the
average
T h y amplitude
X
and phase of the responses evaluated on the Fourier analyzer were calculated
by
the
MINC-11 computer. Replicate
responses
were
combined using vector-averaging. This allowed us' to calcluate the average amplitude and phase of the response over a period of time or
over
several replications.
The amplitude measurements
from
the Fourier analyzer were calibrated on the basis of peak-to-peak ^roltages.
Regan
(18)
"apparent
latency"
repetition
rates.
seconds) portion
was of
has
from For
calculated
described the
the
phase data
each subject the
calculation obtained
apparent
by obtaining the slope of
the phase/repetition-rate function (35 -
at
of
several
latency the
an
(in
linear
55/s)
and
regressions
and
•dividing it by 360. The •
\
data
were
analyzed
using
repeated measures Analyses of Variance. -" *significant at p When
steady
stimulus-rates, latency phase
to
responses
are
obtained
at
different
a latency can be calculated. This latency is the
that portion of the waveform that stays at
regardless of the stimulus-rate.
latency The
state
constant
It can be considered the
to the dominant component of the steady state
response.
method of deriving latency from the averaged data using
the
technique
of Diamond (5,6) is shown for one subject in Figure 6.
The
mean
"derived" latenc” for the 8 subjects calculated
the
Diamond
technique
was 33.3 ms (SD = 8.6).
The
using
"apparent
latency" of the.Fourier-analyzed results was calculated using the method
described by Regan (18). The phase data from the
analysis phase
are
Fourier
plotted against repetition rate in Figure 7. 60/s.
of
The The
mean apparent latency for the 8 subjects was 34.0 ms (SD = 10.8). The
two methods - one a "time-difference analysis", the other
"phase-difference results.
analysis" - thus provide essentially the
The resultant latency of 33 - 34 ms lies in the
of the Pa component of the 10/s transient response.
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a
same range
A u d ito ry s te a d y s t a t e p o t e n t i a l s S ta p e lls e t a l.
\
I
99 r'
-
Insert'Figures 6 and 7 about here
Experiment 3; Stimulus Intensity This
experiment
investigated
intensity on the 40-Hz potential Fourier 10—dB
analysis. steps
condition
from
in
the
effects
of
stimulus
using both signal-averaging and
The 500 Hz tonebnrst was presented at 40/s in 90 to -10 dB nHL. There was
also
a
control
which the earphone was disconnected. The order
of
the intensities was randomized. Behavioral threshold (SL) for the stimulus limits
presented
at
40/s was obtained using
the
method
with
responses
5-dB steps. Replicate waveforms of 2000 S each were recorded using the 51.2 ms sweep
intensity
from 10 subjects. At the same time, the amplitude
phase
the 40-Hz fundamental in the EEG were
of
averaged at
each
*c
of
obtained
and using
Fourier analysis. Figjjr-e amplitude
8
shows the effect of stimulus intensity
of the 40-Hz potential. The results from both
of analysis again parallel each other.
the
methods
The decrease in 40-Hz ERP
amplitude
is
fairly
amplitude
at
90 dB nHL being 1.63 (SD=0.65) and 1.46
linear down to threshold,
with
the
mean
(SD=0.60)
pV,
decreasing to 0.26 (SD=0.10) and 0.16 (SD=0.11) pV at 20
nHL
using
These
!
on
signal averaging and Fourier analysis,
represent amplitude decreases
of 20 nV
dB
respectively.
per decibel. The
•
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I A u d ito ry s te a d y S ta p e lls e t a l .
change
in
s ta te p o te n tia ls
amplitude
was
*
100
quite linear between 90
and
dB
(r = 0.99
for
averaging
are slightly greater than those obtained using Fourier
analysis
mean data). The amplitudes obtained using
20
for
the
same
reasons
as
noted
for
the
signal
preceding
experiment.
Insert Figure 8 about here
The noise level of the recording technique was determined in the
control condition wherein the earphones were unplugged.
noise
level
was 0.18 (SD=0.04) ^iV for signal-averaging and 0.09
(SD=0.06) pV for Fourier analysis. decreases, to
these
noise
The 40-Hz potential amplitude
levels
at
(range=-10 - 40) dB for signal averaging - .40) dB for Fourier analysis. below was
The
intensities
below
13
and below 15 (range=—10
These levels are 4.5 and 2.5
the average behavioral thresholds (SL).
dB
This SL threshold
some 15 dB higher than the nHL threshold because there was a
higher level of ambient noise in the laboratory where the potentials
were
recorded
evoked
than in the sound-attenuated
chamber
first
of
where the nHL was obtained. The averaged with
latency
to
the
vertex-positive
peak
the
response and the phase of the 40-Hz fundamental changes
stimulus
intensity.
The
mean
latency
of
the
averaged
response for the 10 subjects was 7.61 ms at 90 dB nHL, increasing linearly
to
15.46
ms at 20 dB nHL, as shown in
Figure
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9.
A
L
'/
A u d ito ry s te a d y S ta p e lls e t a l.
linear the
B ta te p o t e n tia ls
regression
continuous
101
analysis performed on these data (plotted
line
a slope of
increase
in
obtained
using Fourier analysis were converted to
and
latency
in Figure S) shows
[r = -0.79; p