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Development and psychometric evaluation of the Persian version of the Phoneme Recognition Test: A central auditory processing measure

Objectives The present study aimed to evaluate the psychometric properties of the Persian version of the Phoneme Recognition Test (P-PRT) in normal subjects and cochlear implant (CI) users. Material & Methods This study includes developing the Persian phoneme recognition test (PRT), determining its validity and reliability, and comparing the results of a control group versus CI users. The test reliability was examined through a test-retest with an approximately five-week interval. In the present survey, 363 subjects were investigated in three stages. The face validity evaluation stage was conducted on 40 subjects. The psychometric properties of the P-PRT were evaluated in 323 individuals (225 normal subjects and 98 CI users). The test-retest reliability was examined in all the 225 subjects in the control group and 40 CI users. Results The results confirmed the face validity of the P-PRT. No significant differences were observed between the two genders in terms of performance in the P-PRT. Significant differences were observed between the control and CI groups. Evaluating the test-retest reliability suggested perfect reliability (r>0.9) in both groups. Significant differences were observed in the P-PRT between the adults and the 7-year-old subjects compared to other age groups. Conclusion: The P-PRT can be used as a valid and reliable test for clinically evaluating phoneme recognition abilities and monitoring the rehabilitation progress.


Introduction
Phonemes play a fundamental role in language and speech formation and successful auditory processing (1). They have been conventionally used in clinical auditory diagnosis and rehabilitation irrespective of the presence or absence of hearing loss. According to Luria et al. (1970), reading and writing abilities, such as doing dictations, are significantly associated with auditory phoneme processing abilities (2). Investigating the use of phonemes in scoring speech tests has shown that speech recognition tests based on phonemic examinations provide audiologists with more information compared to that obtained from scoring individual words as a whole. Using phonemes in speech recognition tests encouraged further examinations of speech tests and eventually led to emphasizing phonetically-balanced lists in word recognition tests (3).
According to Luria (1986), the auditory cortex in the left hemisphere (i.e., Brodmann areas 42, 22, and possibly 41) is the region of the brain that processes phonemic data (4) Currently, the SSW is the most widely used CAP test by audiologists working on Central Auditory Processing Disorders (CAPD) (6,7). This may be because of the sensitivity of the test and its accuracy in identifying the diagnostic categories (8). Out of 20 indicators of SSW, seven cases are related to the decoding category (associated with phonemic processing) (9). Due to the importance of scoring patient responses in the test and analyzing phonemic errors using the Phoneme Error Analysis (PEA), a special attention should be paid to the role of phonemes in this model (10). The other test of the Buffalo model, the Phonemic Synthesis Test, is based on recognizing, analyzing, synthesizing, and memorizing the phonemes (11).
Iran J Child Neurol. Summer 2022 Vol. 16 No . 3 In 1996 and 1997, Katz developed and introduced the Phoneme Recognition Test (PRT) for examining phoneme perception (12). The PRT was developed to investigate phoneme perception abilities, specifically in the cochlear implant (CI) users. Masters et al. (1998) reported that disruption in the decoding subcategory at the phoneme level is the basis for auditory processing difficulties in CI users (13). Patients with Auditory Processing Disorder (APD) and CI users share a quite similar problem, as in the case of inability to comprehend a foreign language despite listening to and hearing the sound. The lower speed of speech processing observed in CI users can also be explained by the inability and inadequate capacity of their brain to process large volumes of new sounds over an extended auditory frequency range (13). The recorded version of the PRT was developed to fix problems, such as the variations observed in the results when using a live sound caused by its uncontrollable nature (14). The original version of the PRT can be used to randomly present a total of 34 English phonemes to patients, including 20 consonants and 14 vowels. Each phoneme in the test list is presented to a patient at least twice to ensure the consistency of response. (15).
Also, the important role of phonemes in evaluating patients with APD, normal individuals, and especially CI users should be considered. Given that there is no Persian version of the measure to be used in Iran, the present study was conducted to develop the Persian version of PRT (P-PRT). In addition, we aimed to evaluate the psychometric properties of the developed P-PRT, generate normative data in normal subjects, and investigate the performance of CI users in this test.

Materials & Methods
The present study was conducted in four stages: 1) developing the P-PRT, 2) determining the validity and reliability of the test, 3) generating its normative data, and 4) investigating the performance of CI users in the P-PRT. The data obtained from each stage were successively collected. The study was approved by the Medical Ethics Committee of Tehran University of Medical Sciences (code: IR.TUMS.FNM.REC.1398.140). All adult subjects and the parents of the participating children signed written consent forms, and they were ensured that they could withdraw from the study at any stage.

Developing the P-PRT
The voice of a native Persian male speaker sitting in an acoustic chamber was used to record including six vowels and 23 consonants, five of which (i.e., /g/, /z/, /t/, /s/, and /h/) are homophones.
In other words, in contrast to Arabic, in which these consonants differ in terms of both speech and hearing, in Persian, they differ only in writing.
Given the homophony of these phonemes, their common spoken forms were recorded. Therefore, the P-PRT comprised 28 items, each of which was repeated once in the list. The test phonemes were successively randomized twice to randomly distribute the items in the final list.
Accordingly, 56 items were prepared as the final list of the P-PRT to examine the psychometric properties of this test.

Face validity
Forty subjects were included in the face validity evaluation stage. The recorded version was presented to five audiologists, five speech therapists, five linguists, ten normal individuals, and 15 CI users to report any problems associated with phoneme narration, recording quality and features, as well as audibility and fluency of the instruction (16,17). The final file of the test was developed and prepared for psychometric evaluations after qualitatively investigating the provided comments and making the necessary modifications in the file.

Study population and procedures
To investigate the psychometric properties of the P-PRT, ensure its standardization process, and determine the performance of the CI users and normal individuals in the test, the P-PRT was administered on 323 subjects (152 males and 171 females) aged at least seven years. This population consisted of 225 normal subjects (105 males and 120 females) and 98 CI users (47 males and 51 females). To ensure the integrity of the peripheral auditory system before administering the P-PRT, auditory thresholds for air and bone conduction were investigated at the octave and half-octave frequencies of 250 to 8000 Hz, and speech evaluations were investigated in the normal group. The subjects with an auditory threshold of at least 15 dB HL and a speech discrimination score of at least 96% were included in the study.
Tympanometry was performed with a 226-Hz probe to assess the middle ear, and the subjects with type A tympanogram were included. To evaluate the auditory processing system in the normal subjects, the Persian Phonemic Synthesis

Test (P-PST) and the Persian Staggered Spondaic
Words test (P-SSW) were used, and those with a normal performance based on the normative data of these tests were included in the study (18,19).
The inclusion criteria for the normal control group comprised being monolingual, Persianspeaker with a normal IQ, and being right-handed confirmed by the Edinburgh handedness inventory (20). For the CI group, the inclusion criteria comprised being right-handed, being monolingual, and with unilateral CIs in the right ear for at least one year. Also, all the CI users knew the Persian alphabet well and had undergone complete routine auditory training after cochlear implantation. The functional integrity of the CI was confirmed by the audiologists at the Tabassom Cochlear Implant Center, Ahvaz, Iran, using warble-tone audiometry through loudspeakers in the acoustic chamber. The exclusion criteria comprised fatigue, unwillingness to continue participation in the study, and middle ear infections between the test and retest sessions. In case of no responses, a dash (-) was inserted, and incorrectly-pronounced phonemes were also inserted as pronounced in the relevant place on the score sheet. The obtained score was eventually reported as a percentage and noted at the end of the score sheet. Therefore, the raw score was reported as 0 to 56, and the final score as 0% to 100%.

Discriminant validity
The nonparametric Mann-Whitney U test was used to investigate the discriminant validity of the P-PRT, and evaluate the effect of gender on the performance and score achieved in the test.
This test was also used to compare performance between the controls and CI users.

Reliability
To investigate the test-retest reliability of the P-PRT, a retest was performed on all the 225 subjects in the normal group and the 40 subjects in the CI group five weeks (32±4 days) after the first test. During this interval, the subjects did not participate in any auditory rehabilitation programs, did not consume medications to increase attention and concentration, and developed no middle ear infections; in addition, no significant changes were observed in their overall health status.

Normative data
The mean score of the subjects in normal control group (n = 225) was used to obtain the normative data of the P-PRT. The normal limit was determined using ±1 standard deviation. Moreover, the Kruskal-Wallis test was used to determine the significant differences between different age groups.

Data analysis
The data obtained were analyzed in SPSS software V. 24. The scores obtained from the P-PRT were reported as mean raw scores and percentages. The Kolmogorov-Smirnov test was used to investigate the normal distribution of the data, and face validity was examined qualitatively. The nonparametric Mann-Whitney U test was also used to examine the score differences between the controls and CI users and the performance differences between the two genders. Furthermore, the Kruskal-Wallis test was used to compare the performance of the subjects in different age groups and the Spearman test to examine the test-retest reliability with an interval of approximately five weeks.

Study population
The present study was conducted on 363 subjects

Discriminant validity in investigating differences in performance between the normal subjects and CI users
The results of the Mann-Whitney U test showed significant differences in performance in all the age groups and the entire sample between the normal subjects and the CI users participating in the P-PRT (P<0.05). Table 3 presents the statistical results obtained in these two groups.

Reliability
The Spearman test was used to investigate the relationship between the test and retest scores in all the 225 normal subjects by age group. Reliability was confirmed in all the age groups (r≥0.9).
Assessing the test-retest reliability of P-PRT scores Therefore, the reliability of the P-PRT was confirmed in the CI users and the normal subjects of any age. Table 4 presents the normative data of the P-PRT by age group obtained by administering the test on 225 normal subjects aged at least seven years old.

Normative data
The Kruskal-Wallis test was used to compare the scores between different age groups. T he results showed significant differences at lea s t between two age groups (CI=0.95, Chi-square=85.62, df=6, P<0.0001). The modified Bonferroni mo d el was used for the pairwise comparison of different age groups. According to the results, adults and people aged seven years old were found to be significantly different from the other age groups in the P-PRT (      They found distortion to be a more important problem requiring to be properly addressed. Using recorded test items was highly recommended in other studies and tests for evaluating CI users (21).
The present findings confirmed the face validity of the P-PRT.
Investigating the psychometric properties of the P-PRT found no significant differences between the males and females, which is consistent with the findings obtained in a study on the original version of this test, suggesting no differences in the normative data of the two genders (13).
Investigating the phonemic abilities of CI users constitutes an important and specific application of the PRT. In this regard, Katz administered this test for three purposes as follows: 1) investigating the overall ability to identify spoken voices in CI users, 2) detecting their potential errors more accurately, and 3) investigating changes caused by rehabilitation as a criterion for rehabilitation effectiveness in CI users (15).
Given the importance of the clinical application of this test in CI users, the present study investigated the discriminant validity of this test in them (22)(23)(24)

In Conclusion
The present study developed a valid and reliable

Acknowledgment
The study was based on the approval of the Medical