Reference values for psychoacoustic tests on Polish school children 7–10 years old
Reference values for psychoacoustic tests on Polish school children 7-10 years old
El?bieta A. W?odarczyk 0 2
Agata Szkie?kowska 0 2
Henryk Skar?y?ski 2
Beata Mia?kiewicz 0 2
Piotr H. Skar?y?skiID 1 2
0 Department of Audiology and Phoniatrics, World Hearing Center of the Institute of Physiology and Pathology of Hearing , Warsaw , Poland , 2 Department of Otorhinolaryngology, World Hearing Center of the Institute of Physiology and Pathology of Hearing , Warsaw , Poland , 3 Department of Teleaudiology and Screening, World Hearing Center of the Institute of Physiology and Pathology of Hearing , Warsaw , Poland
1 Department of Heart Failure and Cardiac Rehabilitation, 2nd Faculty, Medical University of Warsaw , Warsaw , Poland , 5 Institute of Sensory Organs , Kajetany , Poland
2 Editor: Andrea D. Warner-Czyz, University of Texas at Dallas , UNITED STATES
Good hearing is a fundamental skill that allows children to develop properly, both socially and intellectually. In contrast to defects in inner ear function, however, auditory processing disorders (APDs)-which can affect up to 2-3% of school-children-are not easily identified with basic screening programs and must be diagnosed using special tests. Although such psychoacoustic tests are available, the scores achieved depend highly on the social, cultural, and linguistic characteristics of the population, and norms must be established for each population separately. Reference values are still lacking for the Polish population, especially for children in school-age, so that practitioners must interpret test scores themselves, often intuitively or using potentially biased thresholds from other countries.
Data Availability Statement: All relevant data are
within the manuscript and its Supporting
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
Materials and methods
We investigated a sample of 94 Polish schoolchildren with normal hearing, divided into four
age groups: from 7 years-olds to 10 years-olds. All children had no speech or language
development disorder, learning problem, or symptom of APD. Participants were volunteers
who had previously taken part in a large screening study. The group consisted of 56 girls
(60%) and 38 boys (40%) with an average age of 8.6 years (SD = 1.1). The test battery
included the Duration Pattern Test (DPT), Frequency Pattern Test (FPT),
Time-Compressed Speech Test (CST), and Dichotic Digit Test (DDT).
The scores on all tests increased consistently with age. The difference between each
agegroup for DPT, CST, and left- and right-ear DDT tests was significant (Kruskal?Wallis test,
p-values = 0.002, 0.006, 0.005, 0.020, respectively), but the effect of age on the FPT test
was not (p-value = 0.143). The analysis showed a clear and significant separation between
a merged group of ages 7 and 8 and another of ages 9 and 10. We, therefore, propose, for
each test, separate reference values for these two particular age-groups. Using thresholds
based on a 10% quantile, we offer the following reference values for ages 7?8 and 9?10
respectively: DPT, 28.5% and 53.8%; FPT, 18.5% and 27.5%; CST, 68.6% and 77.2%;
leftear DDT, 34.3% and 52.5%; right-ear DDT, 56% and 72.5%.
The scores on psychoacoustic tests to diagnose APD differ between cultures and linguistic
backgrounds. Clinicians should, therefore, use norms that have been designed for the
population most similar to their patients. Here, we report the use of a test battery designed for the
Polish language that accounts for various aspects of APD when screening school children.
Together with a full methodology of those tests, we provide norms that can be used as
cutoffs in clinical diagnosis. Practitioners are invited to use them to obtain more accurate,
A large group of patients in audiology and phoniatric clinics are children who, despite good
peripheral hearing as assessed by objective tests, manifest disorders of speech and language
development, articulation disorders, specific difficulties in learning, or another behaviour
which suggests hearing loss. These cases are usually connected with disturbed processing of
acoustic stimuli at higher levels of the auditory pathway and are known as auditory processing
disorders (APDs). It is estimated that as many as 2?3% of schoolchildren [
] can be affected,
which in Poland is estimated at 50?60,000 children. Undetected and untreated, APD adversely
affects the child?s quality of life [
The nature of these deficits makes them very difficult to observe by parents until a child
starts regular school and the first symptoms of deficiencies of hearing ability show up in
comparison to the child?s peers. Even then, although specially designed tools for identification of
APD are available, its diagnosis is challenging, especially in Poland where no established
norms exist. As a consequence, Polish professionals in audiology or phoniatric clinics around
the country use different, unsystematic approaches to diagnose APD, which results in many
false-positives or, less frequently, false-negatives.
As early as 1996, the American Speech-Language-Hearing Association (ASHA) defined and
characterized central auditory processes as those processes and mechanisms in the auditory
system responsible for the following behavioral phenomena: localization and lateralization of
sound sources, sound discrimination (including speech), sound pattern recognition (the
ability to compare current sounds with those in long-term memory), time analysis of auditory
signals, ability to comprehend distorted speech, and the ability to understand speech in the
presence of competing background noise and multi-talker babble [
]. Auditory processing
disorders (APDs) are deficits in one of the above hearing functions. In a report from 2005, ASHA
pointed out the need to assess the extent of APD in the central nervous system and to evaluate
their depth [
]. Electrophysiological tests, such as the auditory cognitive potential P300 and
the mismatch negativity, as well as psychoacoustic tests (also called APD tests or central
auditory function tests), are used in the assessment. Somewhat later, guidelines from the American
Academy of Audiology in 2010 focused on treatment and training regimes to help patients
with APD. However, all researchers have emphasised the need for a systematic approach to
diagnosing APD at an as early stage as possible [
2 / 20
The problem we currently have is that although many of the tests have been created and
used for a long time, they still lack explicit norms and clear clinical guidelines. Jerger and
Musiek created a list of recommended tests for examining children with APD as well as other
tests that could be used for APD screening [
]. However, these authors encouraged every
scientist to create their own control groups since, as they argued, the main difficulty in creating
universal norms lies in the cultural, educational, and linguistic differences between each
population. The test outcome may be affected by both the linguistic characteristics of a particular
language as well as by the linguistic experience of the person being tested. Ideally, therefore,
there should be normative data for each population, at least at the country level. Similar
recommendations for developing individual norms for APD tests are given by Dillon et al. [
On the other hand, it should be noted that Katz et al. have presented an opposing view [
arguing that developing individual norms carries many risks to the quality of the data
obtained. Researchers might end up using different methodologies, quality controls, and
procedures so that the comparison of data from various research centres becomes difficult or
In the case of English-speaking patients, there are many studies and guidelines describing
how to use and interpret different screening tests, both for adults (SCAN?A) [
] and children
]. Some researchers have also investigated other populations and have tried to
define normative datasets for adults, e.g. from Denmark [
] and Spain [
extensive exploration of psychoacoustic tests has been performed for children, driven mainly by two
factors: i) the performance of central auditory processing is highly dependent on age and
develops substantially during the first years of school, and so different age groups will show
significant differences in scores; ii) APD should be diagnosed as soon as possible to allow
countermeasures to be introduced and thus give all children equal chances for development
and learning. In this area, research has included languages such as Dutch [
, or an English dialect from New Zealand [
In 2007, Fuente and McPherson pointed out that there were no norms for the
Polish-speaking population [
]. Recently, two research projects have been conducted in Poland for adults
] and children [
]. The latter is especially relevant and is an important effort to systematise
and structure APD tests for Polish children. However, it has several methodological issues: i)
testing was not performed in an ideal experimental setting and was carried out by multiple
people in various places around Poland; ii) the methodology of the statistical analysis was not
presented in detail, so there was no indication of the type of statistical tests performed or how
multiple comparisons were handled; iii) reference values were determined based on the 1st and
3rd quartiles, which to our best knowledge of the field is not an optimal strategy; iv) the study
was published only in Polish; v) the results were connected to a commercial product offered to
clinics. Although the work of Senderski was no doubt performed with proper diligence and
care, we believe that an independent study in a homogenous environment using consistent
procedures, rigorous statistics, and fully transparent data is still needed.
In this study, we aim to describe the most relevant characteristics of a standard set of
psychoacoustic tests for Polish children of primary school age. The objective is to establish
reference values that can be used as cut-offs in medical practice to identify potential problems and
disorders. We examine children in the age range of 7?10 years. We chose such age limits
because, firstly, such a population is the most important from a practical perspective. In our
clinical experience, we mostly see children of such an age. Secondly, the nation-wide program
of hearing screening in Poland covers exactly that age range. Thirdly, we believe that APD
disorders should be identified as soon as a child starts school. We have therefore focused on the
first four levels of primary school. The test battery we used includes tests that assess
performance of different aspects of central auditory processing: DPT (Duration Pattern Test) and
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FPT (Frequency Pattern Test)?the ability to analyze acoustic events over time [
CST (Time-Compressed Speech Test)?the ability to comprehend distorted speech and
understand speech in the presence of noise [
], and the DDT (Dichotic Digit Test)?the ability to
separate or integrate disparate auditory stimuli between the ears [
]. Research has shown that
these tests are specific and sensitive in detecting a range of central nervous system defects; they
are commonly used in diagnosing APD [
] and form a part of many widely used test
batteries and platforms [
The purpose of this study is two-fold. Firstly, to provide a systematic, Polish-oriented, and
practically proven methodology that could be used to screen APD disorders, based on
normative data in a population of Polish children aged 7?10. Secondly, to characterise the collected
data and devise appropriate reference values. As a result, both our methodology and presented
results permit practitioners to diagnose APD in Polish children systematically.
Materials and methods
The study was conducted at the Institute of Physiology and Pathology of Hearing in Warsaw,
Poland. In total, there were 94 participants aged 7?10 years. All children were recruited from
two local public schools after an area-wide hearing screening program (not psychoacoustic)
that covered thousands of school-aged children in the Masovian voivodeship. All subjects were
volunteers whose hearing was indicated as normal by screening tests: i.e. they had proper
articulation, did not have any speech or language development disorders, no learning problems,
and did not have any symptoms of APD. The children?s legal guardians were informed of the
testing procedures and signed a consent form for their children to participate in the screening
program. The form included a statement that the child is aware of the nature of tests to be
carried out, and hers/his participation is not again hers/his will. Also, before any psychoacoustic
test was conducted oral consents from a representative of the school, the parents and children
were obtained. No participant received any form of financial remuneration.
Each child who volunteered was accepted, as long as she or he fulfilled all the following
1. Peripheral hearing sensitivity within normal limits. Hearing thresholds did not exceed 15
dB HL (pure-tone audiometry using air and bone conduction at 500, 1000, 2000, and 4000
2. Absence of CAPD risk factors. Data were obtained from questionnaires which were filled in
by both teachers and parents. Questions related to potential articulation disorders, learning
problems, impaired development of speech or psychomotor performance, difficulties in
understanding speech in noise, memory disorders, or concentration disorder (see examples
of questions in the S1 Text).
3. Absence of any indication of ear infections or diseases that occurred within a few weeks
preceding the moment of qualification.
4. A participant could not be a student of a music school or systematically participate in
dancing or rhythm classes.
Initially, we qualified 100 children, but three of them were not included in the analysis due
to their age on the day of the experiment (two children were too old, one was too young),
while another three did not complete all tests. Eventually, the group consisted of 56 girls (60%)
and 38 boys (40%) and their mean age was 8.6 years (SD = 1.1). The raw data of individual
participants is available in S1 Dataset.
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The authors did not seek specific permission of the Bioethics Committee to conduct the study
due to the following reasons. i) The conducted tests have an established protocol, are
noninvasive, and routinely used in audiological practice. ii) Participants were primarily those who
took part in a large screening program conducted at dozens of schools in the Masovian
voivodeship. iii) Since 2008, based on a written agreement, the Institute of Physiology and Pathology
of Hearing in Warsaw has implemented a hearing screening program for schools in Warsaw
and Masovia in collaboration with the Health Policy Office of the Capital City of Warsaw, the
Masovian Local Education Authority, and with supervision of the Committee of Clinical
Sciences of the Polish Academy of Sciences. Our study is a side project within the general
program, which is set up as a basis for expanding screening procedures.
To ensure compliance with ethics, the authors had access only to information about the
gender and age of a child, and no other identifying information. In addition, the research was
conducted by a trained person with extensive experience in performing psychoacoustic tests in
children, and under appropriate acoustic conditions. Prior to hearing testing, the children?s
parents were informed of the testing procedures and signed a consent form for their child to
participate in a hearing screening examination. The parents of the children and a
representative of the school in which the study was conducted gave oral consent for children?s
participation in further studies associated with the psychoacoustic tests. All procedures were conducted
in accordance with the Declaration of Helsinki.
Each test was performed by an expert with extensive experience in performing psychoacoustic
tests in children. All sounds were presented at comfortable listening levels for the subjects,
usually 60 dB HL, via headphones (Sennheiser HDA 200) connected to a laptop (HP Compaq
nx7400) via a Creative SB1100 sound card. The study was performed either in soundproof
booths or sound-treated rooms at the Institute of Physiology and Pathology of Hearing in
Warsaw, Poland. All tests were administered in the same order for all participants: firstly FPT,
then DPT, DDT, and finally CST. There was a short break between tests, which length was
decided by the researcher according to his assessment of the child?s fatigue, but no less than 5
minutes. In total, the whole procedure lasted from 1.5 to 2 hours per person. Before each test,
it was confirmed that subjects are willing to participate, and initial instructions were given,
together with a few practice examples. The test was started only if it was certain that the
participant understood the task. The following psychoacoustic tests were conducted.
Duration Pattern Test (DPT). The original version of DPT [
], implemented as a
stand-alone application and available on CD [
], was used. All sounds were presented at a
volume of 60 dB HL for both ears. The task was to listen to three 1000 Hz tones, presented
bilaterally in a random sequence, and identify the length of each tone (short or long). For
example, if the child heard a long tone, a short tone, and a short tone, the correct answer
would be long-short-short. The short tone had a length of 200 ms, while the long tone lasted
500 ms. Tones were separated by 200 ms. For each participant, this task was repeated 30 times
using randomly generated sequences. The score of the test was the percentage of correctly
Frequency Pattern Test (FPT). The original version of FPT [
], implemented as a
standalone application and available on CD, was used [
]. All sounds were presented at 60 dB HL
for both ears. The task was to listen to three 180 ms tones, presented bilaterally in a random
sequence, and identify the frequency of each tone (low or high). For example, if the child heard
a high tone, a low tone, and a low tone, the correct answer would be high-low-low. The
low5 / 20
frequency tone was set to 880 Hz, while the high-frequency tone was at 1020 Hz. Between each
tone, there was an interval of 200 ms. For each participant, this task was repeated 30 times with
randomly generated sequences. The score was the percentage of correctly identified sequences.
Time-Compressed Speech Test (CST). A stand-alone application, available on CD, was
used. A Polish version of this test was developed as a result of scientific cooperation between
the World Hearing Center of the Institute of Physiology and Pathology of Hearing (Poland)
and Brigham Young University Department of Communication Disorders (USA) [
sounds were at 60 dB HL for both ears. The task was to listen to 35 monosyllabic words,
presented bilaterally, and repeat them. Each word was compressed in time by a varying
percentage?from 25% to 80%. The length of each compressed word was shortened by a specific factor,
e.g. a word that usually occupies 1 s and was shortened to 600 ms (i.e. was shortened by 400
ms), so has a compression factor of 40%. The compression factor was increased every five
words and included (in a specific order): 25%, 30%, 40%, 50%, . . ., 80%. The next word was
given after the participant repeated the previous one. All words were generated randomly
from a pre-defined list. The score of the test was the percentage of correctly repeated words.
Dichotic Digit Test (DDT). A stand-alone application, available on CD, was used. A
Polish version of this test was developed as a result of scientific cooperation between the World
Hearing Center of the Institute of Physiology and Pathology of Hearing (Poland) and Brigham
Young University Department of Communication Disorders (USA) [
]. All sounds were
presented at 60 dB HL for both ears. The task was to simultaneously listen to two different digits
in the left ear and two different digits in the right ear and then repeat the digits from both ears.
The digits were monosyllabic and bisyllabic Polish numbers from 1 through 10 matched for
the duration so that the maximum difference in length between the digits presented to the
right and left ear did not exceed 230 ms (there are six bisyllabic and four monosyllabic digits in
the Polish language). Mono- and bisyllabic digits could be mixed within one trial, e.g.
monosyllabic to the left ear and bisyllabic to the right ear. Children were encouraged to guess when
they were unsure of a response. There were 60 pairs of digits (30 pairs in the right ear and 30
in the left), generated randomly. The score was the percentage of correctly identified
sequences, separately for each ear.
All statistical analyses were carried out in R [
]. For all tests, it was assumed that a p-value
below 0.05 indicated rejection of the null hypothesis. Mann?Whitney and Kruskal?Wallis
non-parametric tests were used to test the differences between two or more groups,
respectively. A Benjamini?Hochberg correction was used if multiple comparisons were involved.
All figures were prepared with R?s ggplot2 package. In the case of box plots, boxes represent the
1st and 3rd quartiles, a horizontal line is a median, and a vertical line shows the range between the
lowest and highest value (unless the value exceeded 1st or 3rd quartiles by more than 1.5 of
interquartile range). Observations that did not match those assumptions were treated as outliers and
were marked with a single point. The density of distributions was estimated with Gaussian kernels
(as implemented in the stat_density function of the ggplot2 package).
Reference values were established in specific groups based on the 10% quantile of the
distribution of each test. Additionally, in the S1 Text, we show an alternative approach, based on
calculating two standard deviations from the mean (as recommended by the American Academy
Comparing our results with other studies required an individual approach because
individual data points were not available from the other tests. To get a reliable measure of difference,
we divided the procedure into two steps:
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1. Approximating the distribution of the data from the other study. In cases where only the
mean and standard deviation were available, we assumed that the data followed a Gaussian
distribution. Otherwise, if quantiles were available, linear interpolation was used to
reproduce the cumulative distribution function.
2. Sampling the data and estimating the difference. We sampled the same number of
observations as reported in the original study using either a Gaussian random number generator or
the method of inverse transform sampling. Then we calculated the mean difference between
the sampled dataset and our data. Lastly, the procedure was repeated 100 times to obtain
robust estimates?average difference, together with the standard error. The significance of
the result was then established using a Student?s t-test.
Below we describe the characteristics of the standard test battery of psychoacoustic tests for
sample of Polish school-aged children. Collectively, our data allows to devise reference values
that can be used to flag children with potential disorders.
We focus on age as the primary determinant of psychoacoustic capability in each test, a
parameter which follows consistent findings from various studies around the world [
Based on the results obtained, it is then possible to calculate reference values for each test that
could serve as diagnostic norms. Finally, we compare our data with the results of similar tests
reported elsewhere. Other parameters (e.g. gender) we explored were statistically insignificant
(as shown in the S1 Text, S5 Table and S1 Fig).
Age and psychoacoustic test scores
DPT test. The mean DPT test score increased from 54% for the group of 7-year-olds up
to 77% for the group of 10-year-olds. The standard deviation ranged from 13.3% to 23.6% (Fig
1A). A statistically significant relationship between age and test score was confirmed by a
Kruskal?Wallis test (p-value = 0.002). Pairwise multiple comparisons of separate age groups
(Mann?Whitney test with Benjamini?Hochberg correction) showed a statistically significant
difference between the groups of 7-year-olds vs 9-year-olds (median 53.8 vs 75.0, p-value =
0.014) and between 7-year-olds and 10-year-olds (median 53.8 vs 77.5, p-value = 0.002).
Differences in other comparisons did not reach statistical significance (see S1 Table for p-values
of all comparisons). Basic statistical descriptors of the DPT test scores are shown in Table 1.
FPT test. The mean of the FPT test scores was 45% for 7-year-olds and reached 60% for
9- and 10-year-olds. We present detailed statistics in Table 2. In this case, the relation between
age and test score could not be formally proven (Kruskal?Wallis test, p-value = 0.143). One
reason was the high variability of the test measurements?a standard deviation above 24% for
the whole population and above 21% in each group (Fig 1B), which corresponds to almost half
the mean in each case. Such high variability does not allow one to reliably confirm the
difference between the age groups, despite the tendency previously noted in the means.
CST test. The mean score of the CST test for 7-year-olds and 8-year-olds was 81% and
80.5% respectively, while for 9-year-olds and 10-year-olds it reached 87.8% and 87.1%
respectively. At the same time, the variability of the scores was not high?the standard deviation
varied between 7.1% and 10.9% (Fig 1C). A Kruskal?Wallis test confirmed the significance of age
as a predictor of CST score (p-value = 0.006). Subgroup analysis showed that the difference
was substantial, especially between the 7-year-olds or 8-year-olds compared with either the
9-year-olds or 10-year-olds. Specifically, statistical significance was proven with Mann?
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Fig 1. Distributions of test scores show a consistent increase in central auditory capabilities with age. A) DPT Test. B) FPT Test. C) CST Test. D?F) DDT Test
separated into scores for left (E) and right (F) ears and the difference in scores between the right and left (D). Distributions are presented as boxplots with single points
indicating outliers. In small boxes at the bottom right of each panel are the results of linear regression in which the equation score = ?+? age is fitted. In this way, the
effect of age on the score can be seen; also displayed are the magnitude of the effect (?), the p-value of its significance (pv), and the R2 of the fit.
Whitney test with Benjamini?Hochberg correction for comparison between 7 vs. 9 (median
82.9 vs. 91.4, p-value = 0.023), 7 vs. 10 (median 82.9 vs. 91.4, p-value = 0.038), 8 vs. 9 (median
82.9 vs. 91.4, p-value = 0.023), 8 vs. 10 (median 82.9 vs. 91.4, p-value = 0.023). On the other
hand, the groups of 7-year-olds and 8-year-olds could not be distinguished statistically
(median 82.9 vs 82.9, p-value = 0.925), and the same outcome occurred with groups of
9-yearolds and 10-year-olds (median 91.4 vs 91.4, p-value = 0.925). We present basic statistical
descriptors of CST scores in Table 3.
DDT test. Mean scores in the DDT test for the left ear varied from 53.1% (7-year-olds) to
68.9% (9-year-olds), while the standard deviation varied from 15% to 17.5% (Fig 1E and 1F).
By way of contrast, the scores of the DDT test for the right ear were substantially higher,
increasing from 76.4% (7-year-olds) up to 87.1% (10-year-olds). Variability of the right-ear
DDT was also lower, with standard deviations of 8% to 15.4%. Other statistics are shown in
Table 4. For both left- and right-ear tests, we identified a significant statistical relation between
age and score on the test (Kruskal?Wallis test, p-value = 0.005 and 0.020, respectively). When
we compared subgroups between each other for left-ear DDT with Mann?Whitney test with
Benjamini?Hochberg correction, differences could be formally confirmed when comparing
7-year-olds with 9-year-olds (median 52.5 vs 70.0, p-value = 0.027), and comparing
7-yearolds with 10-year-olds (median 52.5 vs 70.0, p-value = 0.027). Similarly, we obtained
statistically significant results when comparing 8-year-olds versus 9-year-olds (median 57.5 vs. 70.0,
p-value = 0.035) and 8-year-olds versus 10-year-olds (median 57.5 vs. 70.0, p-value = 0.035). In
contrast, groups of 7- and 8-year-olds were statistically indistinguishable (median 52.5 vs. 57.5,
p-value = 0.479), and the same result occurred for groups of 9- and 10-year-olds (median 70.0
vs. 70.0, p-value = 0.886). Subgroup analysis of the right-ear DDT test results showed
significance only between 8-year-olds and 10-year-olds (median 82.5 vs 87.5, p-value = 0.042),
while the other groups did not reach the 0.05 threshold (see S1 Table for p-values of all
Most researchers report that patients usually identify speech-related stimuli to their right
ear with greater accuracy in comparison to their left ear, a phenomenon known as the
rightear advantage (REA) [
]. Many audiologists consider it to be an indication of
left-hemisphere dominance for language. In our case, it is a relevant factor in the DDT Test. We
investigated the REA of the DDT test score (Fig 1D) by subtracting the score of the left-ear DDT
from the score of the right-ear DDT. As reported in most other studies, the right-ear was
consistently positive with a mean of around 20%. Although this effect seems to decrease with age,
it cannot be established statistically (p-value = 0.389). The correlation between the REA and
the test scores was not significant either (see S1 Text and S2 Fig for details), as some
researchers have hypothesised.
Regression model. The above exploration of separate psychoacoustic tests demonstrated
that, apart from the FPT test, the obtained scores are statistically related to age. Nonetheless,
the performed statistical analysis challenge only the existence of the difference between age
groups. On the other hand, as indicated by data, literature and intuition, we would like to
show directionality between age and the score of psychoacoustic tests?i.e. to justify that the
older the patient, the higher the expected score. Therefore, to formally assess this statement,
we carried out linear regression with age as the independent variable and test score as the
dependent variable (see regression curves in Fig 1). Specifically, for each psychoacoustic test,
we fitted an equation
score ? a ? b age;
where ? is the intercept and ? is the coefficient representing the effect of age within the
obtained score. Excluding the FPT test, all other tests had a significant coefficient (?) for the
influence of age on score (p-values: <0.001 (DPT), 0.003 (CST), <0.001 (left-ear DDT), 0.002
(right-ear DDT)), with ? varying from 2.66 to 7.52. For example, in the case of the DDT Test, ?
was 7.52, meaning that an increase of age by one year should give an increase of DDT score by
7.52%. On average, FPT scores also increased with age (? = 4.06), but the uncertainty is too
high to reliably interpret such a result (p-value = 0.082).
Setting reference values
Comparisons of age subgroups performed in the previous section indicate both i) globally
significant relation between age and test scores; ii) a mixed significance when two specific age
groups are set side by side. Indeed, when results of multiple comparisons are carefully
examined (S1 Table), significant differences, in any of psychoacoustic tests, are detectable between
groups of 7-years vs 9-years-olds; 7-years vs 10-years-olds; 8-years vs 9-years-olds; or 8-years
vs 10-years-olds. One the other hand, in every psychoacoustic test, no difference could be
proven to be statistically justified between the groups of 7-years vs 8-years-olds and 9-years vs
10-years-olds. Together, those findings suggest a visible clustering of 7- with 8-years-olds and
9- with 10-years-olds with respect to scores obtained in psychoacoustic tests. Therefore, we
decided to create two larger subgroups for setting the reference values: group I of 7- and
8-year-olds (48 observations), and group II of 9- and 10-year-olds (46 observations). It allowed
us to provide reliable and robust statistical estimates.
Specifically, all group I vs. group II comparisons proved to be statistically significant
by computing with the Mann?Whitney non-parametric test: DPT (median 60.0 vs 75.0,
p-value <0.001), FPT (median 45.0 vs. 61.3, p-value = 0.036), CST (median 82.9 vs. 91.5,
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p-value <0.001), DDT left ear (median 57.5 vs. 70.0, p-value < 0.001), DDT right ear
(median 82.5 vs 87.5, p-value <0.003).
In order to choose the optimal method of calculating reference values, we first investigated
the type of distribution that underlies the data. By analysing the normality of the observed test
scores (see S2 Table), we identified that in the case of CST, FPT, and left-ear DDT, at least two
of the age subgroups failed to pass the Cramer?von Mises test (p-values >0.05). Therefore, for
consistency of analysis, a non-Gaussian approach was followed. Specifically, in each case, we
calculated reference values as a 10%-quantile. The reasons behind such a choice were twofold:
i) we needed to maintain sufficient specificity of any detected disturbance, and ii) 10% is a
threshold considered adequate in other similar studies [
]. The proposed reference
values are reported in Table 5, while comparison with observed data distributions is shown in
When providing reference values it should be noted that the American Academy of
Audiology recommends a separation of two standard deviations [
]; although such an approach is, in
our belief, not sufficiently reliable (for example, when the distribution is asymmetric), we do
report reference values based on ?2 SD in the S3 Table.
Comparison with other studies
As discussed earlier, it is widely accepted that the performance of central auditory processing
is strongly affected by cultural and linguistic background. We, therefore, paid particular
attention to how well our results matched those reported by similar studies from other countries.
Unfortunately, in most studies, the distributions of scores are not fully described. As a
result, we had to use different approaches to compare findings, depending on the amount of
data presented. If only the means and standard errors (deviations) were reported, we assumed
a Gaussian distribution. However, if quantiles were given, we approximated the cumulative
distribution function by linear interpolation and reconstructed the distribution using the
inverse method. Then, comparison with the other study was performed by re-engineering its
data points from the approximated distribution and calculating the average difference with
our study and standard error by bootstrap (sampling repeated 100 times). Statistical
significance was evaluated using Student?s t-test.
Firstly, there is a definite difference between our scores for a childhood population and
those of any study involving adults (over 18 years). We compared our findings to studies from
the USA [
], Netherlands [
], and Poland , all of which have reported DPT, FPT, and
DDT outcomes. In most cases, the difference between our observed scores and scores for the
adult population was substantial and ranged from 12% to 39% for the DPT test; from 28% to
11 / 20
Fig 2. Reference values. Distributions and proposed reference values (solid vertical lines) are given for each test and for two age groups: 7?8
(left, red) and 9?10 (right, blue). A) DPT Test. B) FPT Test. C) CST Test. D) DDT Test. Distributions are shown as density plots (kernel
density estimator), with reference values (10% quantile) marked. Compare with Table 5.
40% for the FPT test; and from 15% to 30% for the left-ear DDT. The only exception was the
right-ear DDT, for which scores of two studies from the Netherlands [
] were comparable.
However, it was not comparable to the study involving American population , where the
right-ear score was larger by 15%.
Our main interest lies in comparing our data with other studies involving school-age
children. We divide the work into two parts i) a comparison with one study from Poland by [
and ii) comparison with studies from The Netherlands [
], Turkey , and New Zealand
]. We summarise all comparisons in Fig 3, which shows all the differences between the
studies mentioned above and our data.
When the DPT test is considered, our measurements are consistently higher than reported
in the literature. Specifically, in comparison with Turkyilmaz et al. (2012) [
] the mean
difference is 7.18% (SE = 3.97, p-value = 0.03), while in comparison with Neijenhuis et al. (2002)
] it is 2.98% (SE = 2.37, p-value = 0.18).
On the other hand, scores for our FPT test are lower compared with all the others.
Differences with the results of Senderski et al. (2016) [
] is ?9.39% (SE = 4.24, p-value = 0.02); with
those of Neijenhuis et al. (2001, 2002) [
] it is ?21.01% (SE = 2.68, p-value <0.01); with
Turkyilmaz et al. (2012)  it is ?23.78% (SE = 4.51, p-value = 0.01); and with Kelly (2007)
] it is ?24.51% (SE = 2.80, p-value <0.01).
The outcomes of the DDT test vary between left- and right-ear measurements. In the
former case, we found an insignificant difference in comparison both with Senderski et al. (2016)
] (diff. = ?2.53%, SE = 3.09, p-value = 0.46) and with Neijenhuis et al. (2002) [
] (diff. =
?0.55%, SE = 1.91, p-value = 0.78). Surprisingly, it is significantly much lower than found by
Kelly (2007) [
] (diff. = ?16.93%, SE = 1.68, p-value <0.01). However, for the right-ear DDT,
our population shows a somewhat larger effect than in comparable studies: the difference with
Senderski et al. (2016) [
] data is 13.27% (SE = 2.01, p-value <0.01), with Neijenhuis et al.
] data it is 8.77% (SE = 2.73, p-value = 0.03), and with Kelly?s (2007) [
] data it is
1.90%, but insignificant (SE = 7.14, p-value = 0.81). However, it should be noted that due to the
specifics of the DDT test and differences between languages, the procedure for this test is not
uniform between studies. In Polish, there are six bisyllabic and four monosyllabic digits between
1 and 10, and in the test, we administered, it is likely that both types of digits were presented
together in a single trial. However, in the English version of this test [
] only monosyllabic
digits are used (nine digits in total, the number 7 is omitted). Also, in Dutch, only one-syllable
numbers are used . As a result, it is reasonable to conclude that the Polish version of this
test has a different degree of difficulty than its counterparts in other languages. On the other
hand, limiting oneself to only one-syllable digits in Polish would introduce, in our opinion, an
even bigger discrepancy with the original test, given the fact that there are only four such digits.
We did not find any study reporting CST test results that would be relevant for comparison
with our population.
Diagnosis of central hearing disorders, especially in children of early primary school-age, is
currently a major challenge for audiologists and pediatric otorhinolaryngologists. Diagnosis of
children is complicated by the co-occurrence of APD with other disorders such as attention
deficit disorder, dyslexia, and specific disorders of speech and language development [
13 / 20
Fig 3. Comparison with other studies. Comparison of results from our study with similar investigations of central auditory processing disorders in children by other
authors (left to right: Senderski , Neijenhuis [
], Turkyilmaz , and Kelly [
]). In every case, we show the difference between our findings (dots and error
bars) and data published in the corresponding publications (dashed lines at zero). Dots indicate mean difference, while error bars are standard errors. We calculated
differences only between comparable groups of observations and then aggregated them by calculating an average difference. Blanks imply no comparable data.
Another difficulty is the lack of clearly defined and widely accepted diagnostic criteria for
central hearing disorders. Currently, auditory processing can be assessed using
electrophysiological tests such as the late latency response auditory evoked potential, the cognitive potentials
14 / 20
P300, and mismatch negativity, as well as behavioural (psychoacoustic) tests. Cortical auditory
evoked potentials and cognitive potentials make it possible to assess the functioning of the
central hearing system in response to acoustic stimuli. However, behavioural tests provide
information on higher hearing functions such as sound localisation and lateralisation, sound
differentiation in terms of frequency and duration, and recognition of sound patterns.
Research has determined that behavioural tests can provide a reliable diagnosis in children as
young as 6 [
The early diagnosis of APD is essential, as it can account for as many as 2?3% of school
children. What is more, our unpublished studies indicate that in groups with additional risks,
APD can happen in 20?30% of subjects with dyslexia and up to 70?80% of cases with specific
language impairment. The earlier the child is sent to an audiologist for APD screening, the
faster she or he can get help and avoid preventable problems in learning and socialisation [
Despite ASHA?s consensus on the diagnosis of APD, the set of tests used by researchers in
different countries differs significantly due to a lack of developed norms and the increasing
number of tests used for screening. All this entails a risk of falsely interpreting a test result as
an auditory perception disorder. It underlines the necessity of developing proper diagnostic
rules and norms that account for the linguistic and cultural aspects of a population which can
then be used in clinical practice. Here, driven by our experience and needs of day-to-day work
with children, we recruited a group of 94 children that represented a normative population of
Polish children 7?10 years old. They were recruited on a voluntary basis from two public
schools from the biggest Polish voivodeship situated in the central part of the country. The
schools were both located in a small or medium-sized city and close to the Polish capital,
Warsaw. Not only were those two schools relatively large in terms of the number of students (more
than 1000 each), but they also have a mix of different socioeconomic and demographic
backgrounds. The children?s parents were either Warsaw-based white-collar workers or engaged in
rural pursuits. The region is an economically attractive destination for Poles migrating from
other parts of the country. Since there were no financial benefits for participation in the study,
socioeconomic bias was avoided. We believe that all the measures we took, including choice of
location and the number of observations collected, contributed to the representativeness of
our sample for the Polish population
The design of the study allowed us to determine norms for four tests: DPT, FPT, CST, and
DDT (both ears). Each test measures different aspects of central auditory processing. Despite a
multitude of available tests, we believe such a battery is an appropriate setting for screening a
general population of children. It contains both non-verbal tests (DPT, FPT) as well as those
that use speech stimuli (words in CST; digits in DDT). Furthermore, all of these tests have a
well-established place and significance in the literature [
] and are suitable for children
]. What is more, Polish versions of CST and DDT were designed under the supervision and
training of Frank Musiek from Brigham Young University Department of Communication
Disorders. The software that facilitates the use of this test battery is available upon contact
from our clinic (i.e. the Institute of Physiology and Pathology of Hearing in Warsaw). We do
not assert that our choice of tests for APD screening is the best possible, as this is probably a
matter of philosophical discussion, still ongoing [
], and additional factors, both culture- and
language-specific, must be taken into account. Nonetheless, based on our long experience, we
are convinced that our proposed tests are good enough to screen children for problems with
APD in Poland, and taking into account the findings presented here, reliable and practical
enough to administer by an audiologist in their day-to-day work.
Specifically, we have proposed reference values of all tests for two groups: 7?8 year-olds and
9?10-year-olds. The reference values can be used as thresholds in diagnosing APD among the
general child population of Poland. Linear regression showed a clear tendency for test scores
15 / 20
to increase with age. However, we could not define reliable cut-offs for each age separately,
because of the lack of significance of some of the between-age comparisons. Part of the reason
was substantial variability in the data, especially in the case of FPT test where a strong relation
to age could not be established. In our opinion, a large variability should be expected from any
child-based psychoacoustic test, since central auditory processing is tightly linked to the child?s
intellectual progress, which can vary substantially between children of the same age. It might
also be suggested that frequency recognition is driven to a substantial extent by unknown
factors not correlated with age. Indeed, the environment of one?s early childhood can have a
considerable effect on the heterogeneity of auditory abilities, as observed in psychoacoustic test
scores. Possibly, a larger sample is needed to make more reliable statistical inferences and set
norms for all age strata.
At the same time, in some cases, the distributions of those tests differed significantly from
Gaussian, sometimes being skewed with long left tails (see Fig 2). The non-normality of our
data was also the main reason behind choosing a quantile-based approach to determine
reference values, instead of the standard-deviation approach (as in [
]). We believe that, due to
non-symmetric data, the latter approach is too conservative and allows for too many
false-negatives in the diagnosis.
It must also be noted that in our data, one outlier is present. Specifically, a child (boy) with
identifier id65 (see S1 Dataset) scored 0% in DPT and FPT tests?he did not correctly guess any
of the presented sound sequences. In preliminary data analysis, we double-checked that this
was not a mistake in data preprocessing or test reporting. Therefore, although it is an outlier in
comparison to other data points, it is not an incorrect observation. Moreover, it was not
unexpected. In our clinical practice, we do occasionally examine children that obtain a zero score in
some of the psychoacoustic tests. Additionally, we checked whether the conclusions of our
study would change, if we excluded the mentioned outlier. We observed no qualitative
differences with results reported in the primary analysis (see S6 Table and details in S1 Text).
Some discussion is needed concerning our recommended cut-offs in the FPT test. The
primary relation between age and the score in this test was found to be non-significant, both by
non-parametric group comparison tests and linear regression. At the same time, comparison
between larger age groups, i.e. 7?8-years-olds vs 9?10-year-olds, did reach significance. Taking
the evidence as a whole, however, one should be cautious when interpreting results of the FPT
test. The scores in this test showed high variability within age subgroups (average coefficient of
variation 0.45 versus 0.33 for other tests). Consequently, even weak performance in
recognising frequency does not necessarily correspond to an abnormal condition and, at least with
respect to our normative data, could be expected. Therefore, our reported FPT thresholds are
relatively low, which seems sound when the normative data has high variability. In our
opinion, the cut-offs provided are well established.
The human auditory system is not symmetric, resulting for most people in a so-called Right
Ear Advantage (REA) that usually decreases from childhood to adolescence until the
midtwenties, and then stabilises at a low level (3?5%). Thereafter, it starts to increase with age [
The implied reasons for this phenomenon are numerous: purely physiological, evolutionary,
or environmental. According to the paradigm, a decrease in REA should be observed in school
children. Our data do not contradict this hypothesis since REA decreases at the level of the
means. However, it is also not supported either, because the observed tendency is not
statistically significant, probably because our study group was too small to detect the REA
dependence on age. In order to thoroughly test the REA hypothesis, we would need to use a wider
age-span of children over 10 years old. For example, Neijenhuis showed a decrease in REA,
but only between 10?12-year-olds, 14?16-year-olds, and adults [
]. For very young children,
contradictory findings have been reported, e.g. Kelly reports only a small decrease in REA with
16 / 20
age (from a very small initial value) [
], while Moncrieff found an inverted-U dependence
between REA and age [
]. Relevant here could also be the specifics of the Polish version of
DDT test used to estimate REA, which was discussed earlier in the Results section (see also
In recent years, a number of papers have been published describing tests used for both
adults and children in different countries [
]. Of course, it is necessary to
analyse children separately from adults, a fact confirmed by the comparison of our results with
data reported in studies involving adults from other countries  as well as from Poland [
When we compared our findings with child-focused studies [
], no clear tendency
can be observed. For any of the compared studies, some of the tests showed higher scores,
while others were lower or statistically indistinguishable. However, from the perspective of
single tests, a slight advantage of our population in the DPT Test and a considerable disadvantage
in the FPT Test were seen.
Results of the left-ear DDT Test were usually comparable with other studies, whereas our
subjects obtained much higher scores in right-ear DDT. However, as mentioned in the Results
section, the specifics of the Polish language in terms of the number of syllables for digit names,
and its impact on the design of the Polish version of DDT test made it difficult to compare
results with those from DDT tests in other languages. It is not easy to say whether the
differences in the number of syllables made the test easier or harder.
Special attention should be given to the work of Senderski and colleagues, in which the
authors analysed a population similar to ours. Nevertheless, the results show substantial
differences. One reason could be the way the tests were performed: in our study children were
assessed by a small group of experts from the Institute of Physiology and Pathology of Hearing
in Warsaw using the same equipment and exactly the same procedures. On the other hand, the
tests reported by Senderski were collected from various clinical and educational centres
around Poland. Discrepancies between our data and the work of Senderski should be resolved
in future work, possibly by conducting a more extensive study with a consistent experimental
Taken together, differences between our data and studies from other countries should be
explained by the way different cultural and linguistic backgrounds influence auditory
processing abilities, which leads to reported discrepancies in how fast children from different
countries develop various aspects of auditory processing [
]. Apart from factors such as the unique
characteristics of a given language, the difficulty of completing tests such as CST or DDT
depends on cultural, educational, and sociological factors. Especially in the case of the DPT
and FPT tests, finding differences with other studies might be questionable, since, at first
glance, these are non-speech tests, without a direct relationship to the subject?s language.
Nonetheless, both those tests measure the capabilities of higher auditory pathways and reflect a
combination of multiple factors. Specifically, populations from different countries are subject
to various confounding variables that can affect the results of tests such as FPT and DPT. One
of these is the fact that Polish children start education later than most children in developed
countries?education is compulsory from the age of 6 in Poland, whereas in Western Europe
and the United States formal education typically begins at age 5. Secondly, the specificity of a
given language substantially influences the environment, in which all central auditory abilities,
not only linguistic, are developed. For example, tonal languages, like Mandarian, in
comparison to the non-tonal language, potentially allows their users to be more sensitive to the sound
frequency. Those are only a few factors among many that should not be overlooked when
interpreting observed results. All of this implies that comparing results of our studies with
those from other researchers shows that norms for psychoacoustic tests always need to be
determined with respect to i) type of test; ii) age of patients; and iii) the particular population.
17 / 20
Our study provides a methodology of screening children for APD, which is adjusted to
Polish linguistic and cultural specifics. Full procedures, software, and assistance in the practical
implementation of the test battery are available upon contact with our clinic. The work is
rounded off with diagnostic threshold values obtained from the normative dataset.
Several aspects of our study that limit its applicability must be noted. Firstly, sample sizes in
some cases were insufficient to unambiguously prove or discard the hypothesis about an
apparent trend with age. Because of relatively small numbers, we had to merge groups of
7and 8-year-olds and 9- and 10-year-olds. An enlarged study might make it possible to
determine reference values for each age group reliably. Secondly, participants of our study came
from the Masovian voivodeship, which represents 14% of the Polish population. There could
be some factor at work that limits generalising from this population to the whole country.
Thirdly, our comparison with results from other studies was based on data provided in
publications, which were sometimes very sketchy. To perform comparisons, we took a conservative
approach, but a direct sample-by-sample comparison would be considerably more accurate.
1. We collected normative data for Polish children aged 7?10 (level 1?4 of primary school) in
terms of performance on psychoacoustic tests related to APD disorders.
2. Reference values used for the diagnosis of APD must be adjusted to both the population
involved and the age of the patient.
3. We propose both a systematic test battery and cut-off thresholds that can be used by
ogists to identify APD among Polish school children 7?10 years old.
S1 Text. Supplementary methods and results.
S1 Table. Detailed results of subgroup analysis with multiple comparison.
S2 Table. Tests for normality to verify distribution of data.
S3 Table. Comparison of reference values calculated using different approaches.
S4 Table. Distribution of patients? gender.
S5 Table. Exploration of age and gender effect.
S6 Table. Influence of the atypical observation on the study results.
S1 Fig. Distributions of test scores according to age group and gender.
S2 Fig. Correlation between test scores and Right Ear Advantage (REA).
18 / 20
S1 Dataset. All individual measurements for DPT, FPT, CST and DDT tests collected in
The authors express their gratitude to Daniel Czarnecki, MA, who provided valuable help in
translating the final version of the manuscript into English.
Conceptualization: Agata Szkie?kowska, Henryk Skar?y?ski, Beata Mia?kiewicz, Piotr H.
Data curation: El?bieta A. W?odarczyk.
Formal analysis: El?bieta A. W?odarczyk.
Methodology: El?bieta A. W?odarczyk.
Project administration: El?bieta A. W?odarczyk.
Supervision: Agata Szkie?kowska, Henryk Skar?y?ski, Beata Mia?kiewicz, Piotr H. Skar?y?ski.
Writing ? original draft: El?bieta A. W?odarczyk, Agata Szkie?kowska, Henryk Skar?y?ski,
Beata Mia?kiewicz, Piotr H. Skar?y?ski.
19 / 20
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