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Contents lists available at ScienceDirect
International Journal of Pediatric Otorhinolaryngology
journal homepage: www.elsevier.com/locate/ijporl
Prediction of frequency-specific hearing threshold using chirp
auditory brainstem response in infants with hearing losses
Zheng-min Xu *, Wen-xia Cheng, Zhi-hong Yao
Department of Otolaryngology-Head and Neck Surgery, Children’s Hospital of Fudan University, 399 Wan Yuan Road, Shanghai 201102, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 19 July 2013
Received in revised form 11 February 2014
Accepted 17 February 2014
Available online xxx
Objectives: To investigate the clinical usefulness of the LS-chirp auditory brainstem response for
estimation of behavioral thresholds in young children with mild to severe hearing losses.
Methods: 68 infants (136 ears) aged 6–12 months (mean age = 9.2 months) with bilateral mild to severe
hearing losses were studied at Children’s Hospital of Fudan University. In all cases, the children were
referred for LS-chirp ABR and visual reinforcement audiometric (VRA) measurements. The lowfrequency band chirp (LF-chirp) thresholds (frequency band = 0.1–0.85 kHz) were compared to the
average VRA thresholds (frequency band = 0.25–0.5 kHz), whereas the high-frequency band chirp (HFchirp) thresholds (frequency band = 1–10 kHz) were compared to the average VRA thresholds
(frequency band = 1–4 kHz) using statistical correlation coefficient values.
Results: The LS-chirp ABR thresholds are very close to behavioral hearing levels. The mean differences
between chirp-ABR and VRA thresholds were within 5 dB HL for all measurements. The smallest mean
threshold difference (<3 dB HL) was obtained for the severe hearing loss group. The correlation
coefficient values (r) were 0.97 at low-frequency and high-frequency bands. For each carrier frequency,
the best correlations between chirp-ABR thresholds and VRA thresholds were obtained at VRA frequency
of 0.25 kHz/LF-chirp (r = 0.98) and VRA frequency of 1 kHz/HF-chirp (r = 0.98).
Conclusions: This study demonstrates the effectiveness using chirp-ABR predicted frequency-specific
thresholds, especially of low and middle frequencies. LS-chirp ABR thresholds determined behavioral
thresholds in patients with severe hearing losses were better than for mild hearing losses. The use of a
chirp-ABR testing ensures higher sensitivity and accuracy than that of auditory stead-state evoked
response (ASSR) for measuring frequency-specific thresholds in young children.
ß 2014 Elsevier Ireland Ltd. All rights reserved.
Keywords:
Chirp-ABR threshold
VRA threshold
Infants
1. Introduction
Approximately one child in every 1000 new-borns has a hearing
impairment in the well-baby nursery population. The incidence of
such a hearing loss in babies admitted to the neonatal intensive
care unit (NICU) is 20–40 times higher [1,2]. Early detection of the
high incidence of hearing loss is very important for early diagnosis
of hearing loss, and then in the benefits of early intervention
focusing on the development of language. A study by Christine
et al. [3] has shown that hearing-impaired children who receive
intervention within 6 months post-conception age have significantly greater potential for speech and language development than
do children receiving intervention at a later age.
* Corresponding author. Tel.: +86 21 64931926; fax: +86 21 64931901.
E-mail addresses: [email protected], [email protected] (Z.-m. Xu).
It is a challenge for clinicians and researchers with current
objective measuring methods to determine hearing thresholds
precisely for infants in their first 6 months of life and consequently
prescribing adequate levels of intervention.
In recent years, the auditory stead-state evoked response
(ASSR) has emerged as an alternative electrophysiological technique for measurement of objective thresholds in young children.
However, several studies have documented high variability in
relationship between ASSR and behavioral thresholds for the
normal hearing and hearing-impaired infants [4–6]. ASSR thresholds in these subjects have been differently correlated to
behavioral hearing level at low frequencies and high frequencies.
In all evoked potentials, synchronization of the nerve fiber firing
is important to generate a large amplitude auditory brain-stem
response (ABR) waveform. The tonepips-ABR evoked potential is
frequency specific since all but the frequency area of the tone pulse
are desynchronized on the cochlea, especially of the low frequency.
The traditional click-evoked ABR is difficult due to the well-know
http://dx.doi.org/10.1016/j.ijporl.2014.02.020
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Please cite this article in press as: Z.-m. Xu, et al., Prediction of frequency-specific hearing threshold using chirp auditory brainstem
response in infants with hearing losses, Int. J. Pediatr. Otorhinolaryngol. (2014), http://dx.doi.org/10.1016/j.ijporl.2014.02.020
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cochlear travel delay whereby frequency areas of the cochlea are
stimulated one after the other [7].
The concept of the chirp was first applied to auditory
electrophysiology by Shore and Nutall [8], and has since been
studied intensively for its use within the auditory field by Elberling
et al. [9]. The CE-chirp is a family of stimuli designed to
compensate for this cochlear travel delay and provide enhanced
neural synchronicity [10]. The stimuli family includes a broadband
CE-chirp as well as narrow band CE-chirp stimuli for frequency
specific testing. In limitation of the CE-chirp application, it is
adequate at lower levels of stimulation (<60 dB nHL). In 2010,
Elberling and Don [11] have developed chirp stimulus that mean
the level-specific chirp-stimulus (LS-chirp). LS-chirp is a broadband chirp that was used with a magnitude spectrum corresponding to that of the click. The LS-chirp will produce larger ABR
amplitudes and better resolution. It should be applied at higher
levels (>60 dB nHL). So, LS-chirp evoked auditory brainstem
response (chirp-ABR) has been regarded as a more synchronous
response than the tonepips-ABR and the click-evoked ABR,
referring to the belief that the chirp stimulates lower-, mid-,
and higher-frequency regions of the cochlea simultaneously
[12,13,9]. The chirp-stimulus generates an optimized synchronous
excitation of neurons in all regions of the basilar membrane. The
stimulus structure allows modification to excite predefined
regions in the cochlear [14].
However, the chirp-ABRs have been investigated in few studies
involving young children with varying degrees of hearing loss.
Only some researchers [10] reported that in this study a variety of
tools were used to analyze the synchronicity of ABRs evoked by CEchirp- and click-stimuli at 40 dB HL in 32 normal hearing subjects
aged 18–55 years.
Our recent study examines the clinical usefulness of the upward
LS-chirp stimulus developed by Elberling and Don [11] in young
patients. We investigate the relationship LS-chirp-ABR and
behavioral visual reinforcement audiometric (VRA) hearing
thresholds for frequency-specific information in a group of infants
with varying degrees of sensorineural hearing loss. In particular,
we examine how accurately the prediction formulae (which were
based on chirp-ABR/VRA threshold correlation data) estimated
hearing threshold in order to find out if it is possible to be used as
the clinical application with regard to diagnostic audiology in
young children.
2. Subjects and methods
2.1. Subjects
68 infants aged 6–12 months (mean age = 9.2 months) with
bilateral mild to severe hearing losses were studied at Children’s
Hospital of Fudan University. In all cases, the children were
referred for chirp-ABR and VRA measurements following failure on
a click-evoked ABR screen assessment (ABR threshold
>40 dB nHL–90 dB nHL in both ears).
Subjects were included only if they showed no evidence of
external and middle ear pathology (normal multiple probe tone
tympanometric results (GSI TympStar) and normal otoscopy in
both ears). Children with deteriorating hearing loss (confirmed by
repeat evoked potential and behavioral assessments) were
excluded. In all subjects LS-chirp ABR and VRA thresholds were
measured binaurally. VRA data (one ear) was correlated with same
ear-specific chirp-ABR data.
2.2. Visual reinforcement audiometric (VRA) measuring
VRA measurements were established for each ear in a soundfield room. The child sat in a chair, and then the test assessed
hearing using earphones in each ear separately. When a sound at a
specific frequency was presented, the child’s eye-shift or head-turn
response toward the sound source was rewarded by activation of a
lighted mechanical toy. The behavioral thresholds were obtained
using conditioned audiometric techniques (visual response
audiometry) with earphones and the 10 dB L down, 5 dB HL up
threshold each procedure. Our clinical audiometer (Dianostic
Audiometer AD229e) was used to generate warble tones at the
frequency range of 0.25-, 0.5-, 1-, 2-, and 4-kHz.
2.3. Chirp auditory brain-stem response measuring
The chirp-ABR was measured with ERA-System Corona Equipment using a pair of ER-3A insert earphones. The level-specific chirpstimulus (LS-chirp) was a broadband chirp that was used with a
magnitude spectrum corresponding to that of the click. Its nominal
edge frequencies were 0.1 and 10 kHz. LS-chirp was modified in such
a way that an equalized acoustical frequency spectrum is obtained
from the output of the ER-3A earphone to excite predefine regions in
the cochlea. The equations defining the chirp were calculated to be
the inverse of the delay-line characteristic of cochlear partition on
the basis of the linear cochlea model. The (acoustic) magnitude
spectrum decreases continuously with increasing frequency.
Therefore the LS-chirp was given two frequency-spectrum bands
that corresponded to the inverse of a model of the amplitude–
frequency response of the ABR. The application of the low-frequency
bands chirp (LF-chirp = 0.1–0.85 kHz) and the high-frequency band
chirp (HF-chirp = 1–10 kHz) provided the possibility of an objective
assessment of the hearing threshold in the respective frequency
range. The chirp-stimuli were presented using maximum level of
100 dB HL with a 21.1/s rate. Responses were recorded for 20 ms
following chirp onset. The chirp-ABR thresholds were obtained
using a 10 dB down, 5 dB up search procedure with a starting level of
approximately 60 dB HL. Threshold was defined as the lowest
stimulus level at which peak wave V could be visualized in the two
frequency bands (the LF-chirp threshold found at wave V peaklatency about 13–14 ms and the HF-chirp threshold found at wave V
peak-latency about 6–7 ms).
2.4. Prediction of hearing threshold using statistic
The LF-chirp ABR thresholds (frequency band = 0.1–0.85 kHz)
were compared to the average VRA thresholds (frequency
band = 0.25–0.5 kHz), whereas the HF-chirp thresholds (frequency
band = 1–10 kHz) were compared to the average VRA thresholds
(frequency band = 1–4 kHz) using statistical correlation coefficient
values. The Pearson r value for each of the test frequency band was
calculated.
3. Results
68 infants (136 ears) with bilateral mild to severe hearing losses
were tested with two different measuring procedures (VRA and LSchirp ABR). The VRA thresholds were measured at 0.25, 0.5, 1, 2,
and 4 kHz in 136 ears of 68 infants, whereas the LS-chirp ABR
thresholds were also performed in 136 ears of 68 infants at the LFchirp (0.1–0.85 kHz) and the HF-chirp (1–10 kHz). The mean chirpABR thresholds at the LF-chirp and HF-chirp bands were compared
with mean VRA thresholds at the frequency bands of the 0.25–
0.5 kHz and the 1–4 kHz. The LS-chirp ABR thresholds overestimated the VRA thresholds in all instances. The mean
differences between chirp-ABR and VRA thresholds were within
5 dB HL for all measurements. Overall, the data show a strong
relationship between LS-chirp ABR thresholds and VRA thresholds.
The correlation coefficient values (r) were 0.97 at low-frequency
and high-frequency bands.
Please cite this article in press as: Z.-m. Xu, et al., Prediction of frequency-specific hearing threshold using chirp auditory brainstem
response in infants with hearing losses, Int. J. Pediatr. Otorhinolaryngol. (2014), http://dx.doi.org/10.1016/j.ijporl.2014.02.020
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Table 1
Mean VRA thresholds and LS-chirp ABR estimates for category 1 (45–65 dB HL) and
category 2 (70–90 dB HL) groups (no. = 136 ears).
Category
Table 2
The frequency distribution of the obtained behavioral and LS-chirp-ABR thresholds
for correlation coefficient values in categories 1 and 2.
Low frequency band
High frequency band
Frequency (kHz)
(0.25–0.5 kHz vs
0.1–0.85 kHz)
(1–4 kHz vs 1–10 kHz)
L-chirp-freq.
(0.1–0.85)
Mean
No.
Mean threshold dB SD
No.
threshold dB SD
Category 1
VRA
Chirp-ABR
Difference
50.5 5.5
55.1 6.3
4.6
58
58
58
50.3 5.4
55.1 6.3
4.8
58
58
58
Category 2
VRA
Chirp-ABR
Difference
78.3 6.1
80.5 6.5
2.2
88
88
88
78.1 6.4
80.5 6.5
2.4
88
88
88
To evaluate further the mean difference between chirp-ABR and
VRA thresholds, the data were divided into two categories based on
chirp-ABR mean threshold-level. The groups were defined as
follows: category 1, mean 45–65 dB HL and category 2, mean 70–
90 dB HL. Table 1 gives the mean thresholds for both procedures as
obtained from each test frequency band and each chirp-ABR
category. The smallest mean threshold difference (<3 dB HL) was
obtained for category 2. In contrast, the infants with chirp-ABR
thresholds less than 70 dB (category 1) were quite different about
5 dB. The results indicated better LS-chirp ABR threshold estimations for the severe group (category 2) at all frequencies (Table 1).
Fig. 1 shows a high degree of correlation between Chirp-ABR
thresholds in both low- and high-frequency audiometry bands in
young patient with severe hearing loss.
Fig. 2 shows the relationship between the chirp-ABR and VRA
hearing thresholds obtained at each frequency band (LF-chirp-ABR
threshold vs mean VRA threshold for 0.25 and 0.5 kHz and HFchirp-ABR threshold vs mean VRA threshold for 1, 2, and 4 kHz) for
all of the ears tested (n = 136). As with the scatter plot, the data
fitted to the line that could mean the great linear regression, which
reflect the fact that chirp-ABR thresholds are very close to
behavioral hearing levels.
To further investigate the relationship between the LS-chirp
ABR and VRA thresholds for frequency-specific information, the
Pearson r values were calculate for each test frequency and each
chirp-ABR category. For each carrier frequency, the best correlations between chirp-ABR thresholds and VRA thresholds were
obtained at VRA frequency of 0.25 kHz/LF-chirp-ABR (r = 0.98) and
VRA frequency of 1 kHz/HF-chirp-ABR (r = 0.98). The results
indicated better LS-chirp ABR threshold estimations for all infants
3
VRA freq.
Category 1
Pearson r
Category 2
Pearson r
H-chirp-freq. (1–10)
0.25
0.5
1
2
4
0.87
0.71
0.88
0.72
0.66
0.91
0.88
0.91
0.88
0.90
with hearing losses at frequencies of 0.25 kHz and 1 kHz that were
within the speech frequency band. For infants with chirp-ABR
thresholds in category 2 (severe hearing losses), the behavioral/
chirp-ABR threshold relationship was stronger than that in
category 1 (mild hearing losses) at 0.25 kHz and 1 kHz (Table 2).
In the LS-chirp ABR thresholds corresponding to the configuration of the behavioral audiogram, F test analyses for all ears showed
no significant difference between chirp-ABR and VRA thresholds
(p > 0.05) in category 1 (mild hearing losses) and category 2 (severe
hearing losses). This finding further revealed a clear relationship still
existed between chirp-ABR and behavioral level.
4. Discussion
The results of our study compare LS-chirp ABR thresholds with
behavioral thresholds obtained by means of visual reinforce
audiometric (VRA) for infants with mild to severe hearing loss. All
LS-chirp ABR thresholds were overestimating behavioral thresholds. The overall, the data show a strong relationship between LSchirp ABR thresholds and VRA thresholds. Correlation coefficient
value (r) was 0.97. The mean difference between chirp-ABR and
behavioral thresholds was 3–5 dB. The majority of chirp-ABR
thresholds (65%) were recorded between 70 and 90 dB (category 2)
from the corresponding behavioral thresholds, and the smallest
threshold difference was within 3 dB. In contrast, the infants with
chirp-ABR thresholds less than 70 dB (category 1) differed with
about 5 dB. This result indicates a closer correlation between chirpABR and severe behavioral thresholds than for mild thresholds
(less than 70 dB HL). These improved correlations for more severe
degrees of hearing loss were in agreement with ASSR/behavioral
threshold relationship in Rance’s study [5]. This increased
sensitivity of the LS-chirp ABR to more severe degrees of hearing
loss may be related to recruitment associated with cochlear
hearing impairment. Elberling et al. [9] explain that the chirpstimulus generates an optimized synchronous excitation of
Fig. 1. A high degree of correlation between chirp-ABR thresholds in both low- and high-frequency audiometry bands in young patient with severe hearing loss.
Please cite this article in press as: Z.-m. Xu, et al., Prediction of frequency-specific hearing threshold using chirp auditory brainstem
response in infants with hearing losses, Int. J. Pediatr. Otorhinolaryngol. (2014), http://dx.doi.org/10.1016/j.ijporl.2014.02.020
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4
100
Mean VRA threshold(dB HL) at 1-4kHz
B
90
80
70
60
50
40
30
40
50
60
70
80
90
100
Mean VRA threshold(dB HL) at 0.25-0.5kHz
H-Chirp-ABR threshold(dB HL)
100
A
90
80
70
60
50
40
40
50
60
70
80
90
100
L-Chirp-ABR threshold(dB HL)
Fig. 2. The distribution of LS-chirp-ABR/behavioral threshold comparisons at each
frequency band for all of the ears tested (n = 136).
neurons in all regions of the basilar membrane. The stimulus
structure allows modification to excite predefined regions in the
cochlea. At high intensity LS-chirp stimulus may be optimally
suited as more sensitive ABR measurements in infants with severe
hearing losses. Our data showed that LS-chirp ABR thresholds
determined behavioral thresholds (mean threshold difference
between 3 and 5 dB) were better than ASSR predicted by
Swanepoel et al. data [6]. This may be that the LS-chirp produce
larger ABR amplitudes and better resolution [9]. We interpret these
results as a compatible with the concept of better hair-cell
synchronization.
As with the frequency-specific information, the data with the
scatter plot (Fig. 2) fit to the linear regression, which reflect the
fact that LS-chirp ABR thresholds are close to behavioral hearing
levels at LF-chirp/VRA (0.25–0.5 kHz) and HF-chirp/VRA (1–
4 kHz). Pearson correlation coefficients were calculated to assess
the relationship between chirp-ABR frequency-band (LF-chirp
and HF-chirp) and behavioral thresholds at each frequency. Our
data showed that the best correlations between LS-chirp ABR
thresholds and VRA thresholds were obtained at VRA frequency of
0.25 kHz/LF-chirp-ABR (r = 0.98) and VRA frequency of 1 kHz/HFchirp-ABR (r = 0.98). These results imply better LS-chirp ABR
threshold estimations for infants with hearing losses at frequencies of 0.25 kHz and 1 kHz. They are very important low-middle
speech frequency bands for clinical application. However,
Swanepoel et al. [6] reported that the largest mean difference
between ASSR and behavioral thresholds was at 0.5 kHz, and it
was the only frequency indicating a statistically significant
difference between ASSR and behavioral thresholds. Problems
in estimating 0.5 kHz ASSR have been reported previously [15,16],
and could result from the fact that the low-frequency-evoked
response has a greater intrinsic jitter, due to neural asynchrony.
Another reason may be that stimulus protocols for amplitudemodulated tone at 0.5 kHz are not yet optimal. So, the ASSR
predicted thresholds are not suitable in estimating low frequency
thresholds, especially of 0.5 kHz. Our result revealed more
sensitive LS-chirp ABR measurement in estimating low-middle
frequency thresholds (0.25–1 kHz). There may be factors which
explain the higher correlation between the LS-chirp ABR and
behavioral thresholds at low-middle frequencies. The LS-chirp
evoked ABR has been regarded as a more synchronous response
than the click-evoked ABR, referring to the belief that the chirp
stimulates lower-, mid-, and higher-frequency regions of the
cochlea simultaneously, especially of lower-, middle-frequency.
Don et al. [17] found that the low-chirp-stimulus evoked a
significantly larger amplitude of the ABR than that of a click-ABR.
Table 2 show the frequency distribution of the obtained
behavioral and chirp-ABR thresholds in categories 1 and 2. These
data further confirmed the best chirp-ABR threshold estimations
for infants with sever hearing losses at frequencies of 0.25 kHz and
1 kHz.
In this study, there are some limitations of using the LS-chirp
ABR that are considered in the following. The chirp stimulus
designed from two bands (LF-chirp = 0.1–0.85 kHz and HFchirp = 1–10 kHz) that could not be precisely correspond to VRA
frequency bands (0.25–0.5 kHz and 1–4 kHz). Thus, the chirp may
represent the frequencies of 0.25 kHz, 0.5 kHz, 1 kHz, 2 kHz, and
4 kHz that are correspond to VRA frequencies. The problem is also
that chirp stimulus fixed by instrument is split between 0.85 kHz
and 1 kHz in this study. When the instrument (stimulus
parameters) is improved, we will further study in this issue for
relationship between VRA and LS-chirp ABR thresholds.
In conclusion, this study demonstrates the effective implementation of LS-chirp ABR predicted frequency-specific thresholds,
especially of low-middle-frequency. LS-chirp ABR thresholds
determined behavioral thresholds in patients with severe hearing
losses were better than for mild hearing losses. The use of a chirpABR testing ensures higher sensitivity and accuracy than that of
ASSR for measuring frequency-specific thresholds. It is possible to
be used as the clinical application with regard to diagnostic
audiology in young children.
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Please cite this article in press as: Z.-m. Xu, et al., Prediction of frequency-specific hearing threshold using chirp auditory brainstem
response in infants with hearing losses, Int. J. Pediatr. Otorhinolaryngol. (2014), http://dx.doi.org/10.1016/j.ijporl.2014.02.020