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Year : 2019  |  Volume : 25  |  Issue : 2  |  Page : 71-75

Development of dichotic digit test in Tulu

Department of Speech and Hearing, SOAHS, Manipal Academy of Higher Education, Manipal, Karnataka, India

Date of Web Publication16-Aug-2019

Correspondence Address:
Ms. P G Bhargavi
Department of Speech and Hearing, SOAHS, Manipal Academy of Higher Education, Manipal - 576 104, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/indianjotol.INDIANJOTOL_119_18

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Introduction: Behavioral tests are widely used due to their ease of accessibility, simple instrumentation, less variability, and feasibility for interpretation. The use of these tests in regional languages such as Tulu will make the individuals comfortable. Tulu is spoken as mother tongue by over 2 million people in India which demands the need of development of test. Methodology: The study was done in two phases. In Phase 1 of the study, development of material was done which included two lists (List A and List B – each containing 20 digit pairs). In Phase 2 of the study, the recorded material was administered on normal population. Sixty-six native Tulu-speaking adults of age range18–55 years consented and participated in the study. These adults had no associated sensory-motor deficits or history of middle ear effusion and audiological evaluation showing pure tone average ≤15 dBHL; speech identification score (SIS) >90%. Statistical Analysis: Descriptive statistics was used to compile mean and standard deviation and paired sample t-test was used to check the statistical significance between the ears. Results: The present study revealed a significant difference between the right ear and left ear, indicating of greater right ear advantage in Tulu speakers. Conclusion: Language plays an important role in performance of behavioral tests used, even in central auditory test battery, which led to development of test in Tulu. The scores obtained from this test can be utilized in demarcating the normal population from peripheral loss, central auditory processing disorders, cortical/brainstem lesions, and dyslexic groups, in Tulu-speaking population.

Keywords: Dichotic digit test, language, right ear advantage

How to cite this article:
Bhargavi P G, Kanaka. Development of dichotic digit test in Tulu. Indian J Otol 2019;25:71-5

How to cite this URL:
Bhargavi P G, Kanaka. Development of dichotic digit test in Tulu. Indian J Otol [serial online] 2019 [cited 2021 May 13];25:71-5. Available from: https://www.indianjotol.org/text.asp?2019/25/2/71/264671

  Introduction Top

Hearing is said to be a complex phenomenon and the importance of it is often taken for granted. The acoustic signals get converted to neural signal as it passes through the auditory pathway and finally leads to comprehension. In individuals with hearing loss, we think that ability to detect the presence of sound is lost, in reality, it is just one part of the processing which occurs in auditory system.[1]

Individuals who do not have any difficulty for detecting the presence or absence of sound may have other difficulties related to perception of sounds (e.g., difficulty in understanding speech in noisy situations, and problems in understanding complex commands) which can affect development of language in children, schoolgoing child might have academic difficulties, and adults and geriatrics may face difficulty to communicate effectively. Their difficulties are misinterpreted with reasons such as attention deficit, behavioral problems, lack of motivation, or due to some other cause. These difficulties occur due to processing difficulties, which occur in central auditory pathway. An individual who has these difficulties is more likely to have problems with respect to central auditory processing skills.[1]

Central auditory processes include few mechanisms which are as follows: sound localization and lateralization; auditory discrimination; temporal aspects of audition, including temporal resolution, temporal masking, temporal integration, and temporal ordering; auditory performance with competing acoustic signals; and auditory performance with degraded signals. These processes are applicable to verbal as well as the nonverbal stimulus, and any difficulties with these processes, the individual may have speech and language problems.[2] When there are deficits seen in one or more of the processing skills previously listed, it is termed as central auditory processing disorders (CAPD).

Researchers have estimated the prevalence rate of CAPD to be approximately 2%–5% in the school-age population. CAPD is more prevalent in boys than in girls by a ratio of 2:1.[3] Reports of the prevalence of APD in the older adult population vary, ranging from well over 50% in clinical studies[4] to around 23% in a longitudinal population study.[5] However, the prevalence and incidence of CAPD are not clear in the Indian population.

There are numerous tests designed to assess the various central auditory functions of the brain. These tests can be broadly categorized as behavioral and electrophysiological tests. Behavioral tests most often used in routine clinics as they provide information related to areas requiring focus during the management.[6] Advantage of these tests is easy administration and inexpensive. Few tests to name – dichotic digit test (DDT),[7] DDT revised,[8] dichotic rhyme test,[9],[10] dichotic sentence identification test,[11] and staggered spondaic word test.[12] Among all these tests, DDT has been the most popular because of its simplicity of test items, ease of administration, stimulus load, high sensitivity to central lesions, and potential clinical feasibility.[8]

DDT is a central auditory test that assesses binaural integration skills, that is, the ability of the listener to process different information being presented to each ear at the same time. DDT is ideal to be used because digits stimuli generally are familiar to most listeners of all ages.

Need for the study

Language plays a very important role in speech identification, and grammatical structures in Indian languages are quite different from those of English. Testing in foreign language or adapting the norms of Western language is therefore not acceptable. This could result in poor scores in performance of the test. The stimulus used should include items that are familiar to one's language,[13] and it is always better to have norms for our own area.[14]

Behavioral tests are still widely used due to their ease of accessibility, simple instrumentation, less variability, feasibility for interpretation, and availability of normative. Thus, behavioral tests are useful clinical tools in Central auditory nervous system (CANS) evaluation. One such test is DDT.

Although DDT is available in Kannada (a native language of Karnataka state), it is seen that a large number of population residing in the coastal Karnataka still communicates only in Tulu. More than 1.72 million have Tulu language as their mother tongue.[15] Literature regarding normative performances in Indian languages such as Tulu is less, even though the existence of these tests is since 1961. Hence, the need of the study is to develop DDT in Tulu.

Aim of the study

The main aim of this study was to develop DDT in Tulu.


The objective of this study are as follows:

  1. To develop DDT in Tulu
  2. To obtain normative data for DDT in Tulu
  3. >To check the reliability of test on normal individuals.

  Methodology Top

Study site

This study included people from Udupi and Dakshina Kannada districts. The testing was carried out at the Department of Speech and Hearing, SOAHS, Manipal.

Phases of study

The study was done in two phases:

  • Phase 1: Development of the stimulus
  • Phase 2: Normative estimation.

Study population

Sixty-six normal hearing Tulu-speaking adults participated in the study.


Flow chart [Figure 1] explains the procedure in steps.
Figure 1: Flowchart depicting the procedural steps

Click here to view

Step 1: Ethical committee clearance

Ethical consent was obtained from the institution and hospital where the study was carried out. To the participant, the test procedure was explained and necessary consent was obtained before the initiation of the study.

Step 2: Development of test material (Phase 1)

This step involves formulation and recording of the test material.

Formulation of test material

Original word list was developed by selecting digits from 1 to 10. Once the digits were selected, the digit pairs were prepared. While preparing the digit pairs, it was ensured that combinations containing repeated digits were excluded, for example, combinations such as 1-1; 2-2 were excluded from the study. Two lists were then prepared, that is, List A and List B. Care was also taken that reverse digit combination was not included in a pair (1-2; 2-1). The selection of these test items was on the basis of randomization. Thus, two lists (List A and List B) containing 20 digit pairs each in Tulu was prepared.

Recording of material

Recording of the words (digits) spoken by an adult native female speaker was done in a sound-treated room as recommended by the ANSI standards[16] using PRAAT (v 4.2.18) software, Institute of Phonetic Sciences - University of Amsterdam. The spoken signal was sampled at 44,100 Hz with a resolution of 16 bits while recording. The recorded file was processed further in Audacity software (version 1.3). The Audacity team, Carnegie Mellon University, Pittsburgh, Pennsylvania. Calibration tone of 1 kHz whose intensity was equivalent to average intensity of all digits was generated and inserted before the starting of the test stimulus. A stereo track was then created, where the digit pair was aligned in the right and left channel (two digits in each channel). The intensity levels of the digits were normalized and interdigit interval was set to 0.5 s. The intertrial interval was examiner controlled. Thus, the overall test containing 80 test items with 40 digits for each ear with two lists was formed (List A and List B – each containing 20 digit pairs). The material was converted into audio CD format.

Step 3: Normative estimation (Phase 2)

The DDT in Tulu was then administered on 66 normal adults (31 males and 35 females). The mean age for the participants was 34.1 years. The participants ranged in their vocational and educational background such as college students, nonteaching staffs, drivers, technicians, hospital janitors, and homemakers. The inclusion criteria were as follows:

  • Native speakers of Tulu
  • Age range: 18–55 years (both males and females)
  • No associated sensory-motor deficits
  • No history of middle ear effusion
  • Routine audiological evaluation within normal limits (PTA <15 dBHL; SIS >90%).

Instrumentation and test environment

Before the administration of the test material, audiometric thresholds were estimated for both ears, across frequencies of 500 Hz to 8 kHz using Modified Hughson and Westlake procedure.[16] Speech audiometry was also carried out using GSI-61 Clinical Audiometer (headphones-TDH-39) in order to ensure normal speech identification scores. In addition, middle ear function was assessed using GSI-Tympstar middle ear analyzer.

Test administration procedure

The dichotic digits were reproduced using a Sony portable CD player D-NE700 ATRAC 3 PLUS. The output was routed through a calibrated GSI-61 clinical audiometer with headphones (TDH 39). The entire testing procedure was carried out in sound-treated double room condition, with ambient noise levels within permissible limits.[17]

Instruction to patient

The participants were instructed that “You will hear four digits, two in each ear. Listen carefully to both ears and repeat all the digits that you hear. The order is not important and you are allowed to guess the numbers. The first few items will be for practice.” A practice session consisting of three sets of digit pair was presented before the actual test.

Step 4: Scoring and data analysis

Participant's response was recorded in a sheet. If the participant repeated all the digits (irrespective of the order), it was considered as a correct response. Each correct response was given a score of “1” and incorrect responses were scored “0.” The number of correctly reported digits for each ear was counted and a percentage was obtained. Each correctly identified digit sets was given percentage weightage of 5%, thus the total possible score that could be obtained was 100%.

Descriptive statistical analysis of the scores in terms of mean, standard deviation (SD), range, minimum, maximum, and 95% confidence interval was carried out. Paired sample t-test was used to reveal the statistical significance between the right and left ears. Test–retest reliability was also carried out. Statistical Package for the Social Sciences (SPSS) (version 16) IBM Corporation, Chicago was used.

  Results Top

The first step was development of the list. Two lists (List A and List B) were prepared with 20 digit pairs each in the list and set of three pairs were included as test items. The selection of the digit pairs was based on randomization. The final list containing the digit pairs in Tulu is shown in [Table 1].
Table 1: Dichotic digit test in Tulu

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For the estimation of normative value, the developed test was administered on 66 normal native Tulu speakers. All the speakers were administered the two lists (List A and List B). The obtained raw scores were converted to percentage correct score and analyzed using SPSS 16.0 software. Descriptive statistics, such as mean (SD), minimum, maximum, and 95% confidence interval (lower and upper), were estimated for both the ears. To check whether there is a significance difference (at 0.05 level) in scores between the right and the left ears, the mean percentage scores were compared. Paired sample t-test was done between the mean percentage scores of the right and the left ears. The result is depicted in [Table 2].
Table 2: Percentage correct scores on dichotic digit test in Tulu

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Mean value in percentage

From [Table 2], it is seen that, for the right ear, the mean score (in percentage) obtained was 95.15 with a SD of 2.95. The minimum value being 88.7 and the maximum value was 98.7. The 95% confidence interval ranged from 94.4 (lower) to 95.8 (upper). For the left ear, the mean score (in percentage) obtained was 89.5 with a SD of 3.5. A minimum value of 78.7 to maximum value of 97.5 was obtained. The 95% confidence interval ranged from 88.6 (lower) to 90.4 (upper). The results of the right and left ears showed P = 0.036.

  Discussion Top

The results of the present study showed a better right ear score than the left ear, which is in congruence with other studies reported.[7],[8],[18],[19],[20] In a study done by Musiek[8] in English language, they found that the mean scores obtained in percentage are 97.8% in the right ear and 96.5% in the left ear. The better percentage obtained could be attributed to less number of individuals tested and language used. These studies reported that the digits presented to the right ear were perceived better than left ear both in normal as well as individuals with central nervous system lesions and temporal lobectomy patients. Dirks studied the adult population where he observed not only right ear superiority but also showed cerebral dominance (left hemisphere) in 2%–6% for dichotic digits.[21] Hence, we can see from the literature that dichotic digits give insight into central processing skills not only in normals but also in individuals with lesions. These findings suggest a possible right ear advantage.

The scores of DDT vary widely in different languages. The DDT test developed in Kannada, Telugu, Hindi, and Indian English, the age-matched normative criterion was set as 90% and below it was abnormal.[22] This was similar to DDT developed by Musiek.[8] However, in Western studies, this criterion level varies with language and age. In the current study, the mean scores in percentage obtained were 95% for right ear (with lower and upper limits of 94%–95%) and 89% for left ear (with lower and upper limits of 88%–90%) based on 95% confidence interval. Thus, from the present study, the criterion level of above or >90% for right ear and above or >88% for left ear is established, indicating of greater right ear advantage even in Tulu speakers. However, individual variability should always be accounted for and cannot be ruled out.

To estimate the test reliability, the test was readministered again on 10 normal native Tulu speakers after 1 week. These normal native speakers were randomly drawn from the already tested groups. Descriptive statistical analysis was done and the obtained scores are depicted in [Table 3].
Table 3: Percentage correct scores on test-retest reliability

Click here to view

Mean value is in percentage

The mean value (in percentage) obtained for the ten samples for the right and left ear was 93.25 and 89.15, respectively. The SD obtained for the right and left ear was 4.6 and 6.4, respectively. The P value of 0.03 was obtained, suggesting that values are statistically significant. It was observed that the mean scores (right ear: 95.15; left ear: 89.54) obtained for 66 normal individuals were comparable to the mean scores of 10 adults after 1 week. This indicates that the test results are replicable, suggesting good test–retest reliability. This is in congruence with the studies reported earlier.[8],[22]

Limitation and future recommendation

Although the normative has been established, the clinician can use this only after administering the developed test on pathological groups with known lesions, auditory processing disorders, and learning disabled. This will help in establishing the sensitivity and specificity of the test and thereby improving its validity as a clinical tool.

The present study was carried out on only 66 normal participants for estimating the cutoff scores; however, it is felt that the future studies could use larger sample size to strengthen the findings of this study. Future research could focus on administering the test on pathological group, as even though peripheral hearing loss does not affect the performance of DDT, there should be criterion level demarcating hearing-impaired population with and without CAPD.

Due to the simplicity of the stimulus material, this test is easily applicable even for children; however, the criterion level obtained for adults cannot be directly applied in children, as Musiek reports of improvement in scores with age from 7 to 12 years for both the right and left ears.[8] This occurs due to the maturation of auditory processing skills. Thus, the future research should include administrating the developed test on children with varying age groups and documenting the developmental changes longitudinally rather than crosssectionally.

  Conclusion Top

It can be said that the current material though developed and administered only on normal adults, it can also be used in children as it is very simple and easy. However, the sensitivity of this test could further be established by administering on individuals with APD, peripheral hearing disorders with different degree/type of hearing loss, and other disorders such as learning disability, cortical lesions, and brainstem lesions. Future research should be taken up in administrating the developed test on children as well as adults with varying age groups and documenting the developmental changes longitudinally rather than mere documentation in cross-sectional manner.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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American Speech-Language-Hearing Association, Task Force on Central Auditory Processing Consensus Development. Central auditory processing: Current status of research and implications for clinical practice. Am J Audiol 1996;5:41-54.  Back to cited text no. 2
Chermak GD, Musiek FE. Central Auditory Processing Disorders: New Perspectives. San Diego: Singular Pub. Group; 1997.  Back to cited text no. 3
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Cooper JC Jr., Gates GA. Hearing in the elderly – The Framingham cohort, 1983-1985: Part II. Prevalence of central auditory processing disorders. Ear Hear 1991;12:304-11.  Back to cited text no. 5
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Kimura D. Cerebral dominance and the perception of verbal stimuli. Can J Psychol 1961;15:166.  Back to cited text no. 7
Musiek FE. Assessment of central auditory dysfunction: The dichotic digit test revisited. Ear Hear 1983;4:79-83.  Back to cited text no. 8
Wexler BE, Halwes T. Increasing the power of dichotic methods: The fused rhymed words test. Neuropsychologia 1983;21:59-66.  Back to cited text no. 9
Musiek FE, Kurdziel-Schwan S, Kibbe KS, Gollegly KM, Baran JA, Rintelmann WF, et al. The dichotic rhyme task: Results in split-brain patients. Ear Hear 1989;10:33-9.  Back to cited text no. 10
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Katz J. The use of staggered spondaic words for assessing the integrity of the central auditory nervous-system. J Aud Res 1962;2:327-37.  Back to cited text no. 12
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Population Census of India; 2001. Available from: http://www.censusindia.nets. [Last accessed on 2009 Dec 06].  Back to cited text no. 15
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American National Standards Institute Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms (ANSI S3.1-1991). New York: American National Standards Institute; 1992.  Back to cited text no. 17
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Musiek FE, Baran JA. Central auditory assessment: Thirty years of challenge and change. Ear Hear 1987;8:22S-35S.  Back to cited text no. 19
Moncrieff DW, Musiek FE. Interaural asymmetries revealed by dichotic listening tests in normal and dyslexic children. J Am Acad Audiol 2002;13:428-37.  Back to cited text no. 20
Dirks D. Perception of dichotic and monaural verbal material and cerebral dominance for speech. Acta Otolaryngol 1964;58:73-80.  Back to cited text no. 21
Shivashankar N. Development of central auditory speech tests in Indian languages. J Indian Speech Hear Assoc 1990;7:347.  Back to cited text no. 22


  [Figure 1]

  [Table 1], [Table 2], [Table 3]

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