N. Shivashankar, National Institute of Mental Health and Neurosciences
India poses a unique challenge for the audiologists and speech-language pathologists dealing with central auditory processing disorders (CAPD). These challenges are multifaceted because India is a multi-lingual country and people hail from various socio economic backgrounds. This makes it hard to develop uniform CAPD tests in different languages. Further, CAPD testing, unlike basic pure-tone audiometry (PTA) or for that matter, Auditory Brainstem Responses (ABR), is not a part of the routine evaluation or a part of an audiologists’ conscience thinking unless, audiologists are housed in academic institutions or tertiary care hospitals where there is a dedicated department of Speech Pathology and Audiology. Apart from neuro-psychiatric institutions/departments where both children and adults with CAPD are evaluated, the other place where children with CAPD can be identified is at school. Since there are very few school speech pathologists and audiologists, identification of CAPD in school, takes a back seat.
According to the website of the Rehabilitation Council of India, a statutory body under the government of India, there are more than 55 colleges offering undergraduate (UG), post graduate (PG) courses in speech pathology and audiology. However, the Indian Speech and Hearing Association (ISHA) on its website documents only about 49 institutes that are actively running the program (this needs to be updated) with a total intake varying from 25 to 60 students depending on the institutional infrastructure. About 5 speech and hearing institutes are offering a Ph.D. program. Only one institute is offering post-doctoral program. Currently as per the record of ISHA there are 2495 practicing professionals who are members of ISHA. Of them several members are working/studying abroad and this leaves an abysmally small number of professionals to cater to the needs of 63 million (6.3%) hearing disabled population (Garg, Chandha, Malhotra and Agarwal, 2009). The 63 million estimate does not include those suffering from CAPD. Hearing loss per se due to conductive pathology or known congenital hearing impairment gets better noticed because of fair understanding of these conditions amongst the professionals. However, awareness among professionals in identification of CAPD is very poor. The rest in terms of management goes unsaid.
Evaluation of CAPD in India was first initiated in the 80’s in patients with neurological disorders. The first study was “Development of Staggered Paired Word Test (SPW) in Kannada language” and it was validated on space occupying lesions of the central nervous system (Nagaraja, 1988), and the second was “Central auditory evaluation in post-traumatic syndrome” (Shivashankar, 1988), where Ipsilateral-Contralateral Competing Sentence Test (IC-CST) in Kannada language was developed for the purpose of the research. Gradually several other central auditory speech tests (CAST) were developed in Indian languages for evaluating patients with neurological disorders (Shivashankar, 1991).
Studies on CAPD in children was initiated by Shivashankar and Gururaj (1993) who reported 29.6% children amongst those diagnosed with learning disorder had CAPD based on the modified – auditory behavior screening profile by Willeford and Burleigh (1985). Large scale epidemiological studies in the area of CAPD are lacking. Muthuselvi (2009) and Muthuselvi and Yathiraj (2010), reported prevalence of CAPD of 3.2% in school-aged children. This is similar to the findings reported by Chermak and Musiek (1997) accounting for 2–3% of school-going children. Existence of CAPD as a co-morbid feature can be also seen widely in many neurodevelopmental conditions such as Attention Deficit Hyperactive Disorder (ADHD), Autism Spectrum Disorder (ASD) as well as in neurological lesions such as cerebro-vascular disorders, degenerative lesions, trauma, space occupying lesions etc. Children with no co-morbid features demonstrating academic or listening difficulties have to be examined for the presence of CAPD.
Young researchers like, Dr. Asha Yatiraj and Dr.Vanaja took a keen interest in this area and spearheaded CAPD research in the country in the 90s. Two screening tools in the Indian context are now available viz., Screening checklist for auditory processing (SCAP) (Yathiraj and Maggu, 2013) and Screening test for auditory processing (STAP) (Yathiraj and Maggu, 2014).
With increase in generation of man-power in Speech and Hearing across the country, there is an increase in the development of various CAPD tests in many Indian languages over time, as a part of the obligatory course work at the post-graduate and doctoral level. Tests that have been developed for central auditory evaluation include; 18 Dichotic tests, 3 Binaural Fusion Tests, 3 Filtered Speech Tests, 2 Staggered Spondaic Tests, 3 Synthetic Speech Identification Test, 8 SPIN Test, 11 Temporal Tests, 5 Auditory Memory and Sequencing Test, 4 Behavioral Check lists. Few tests of CAP are available in few Indian languages such as; Kannada, Tamil, Telugu, Marathi, Hindi and Malayalam. Few tests have been developed in English relevant to the Indian context.
Most of the tests that have been developed are used by centers where they have been developed and are being applied to specific groups of patients who commonly report there. For example, the tests that have been developed in a neuropsychiatric institute such as NIMHANS are largely used in neurological patients and occasionally in psychiatric clientele. Some of the CAPD tests that have been frequently used in a neuro-psychiatric set-up are; dichotic tests, environmental sound perception test, gap detection, pitch pattern and duration pattern and masking level difference.
Non-speech tests enjoy a more prominent place than speech based tests because of linguistic diversity prevailing in our country. However, employing only non-speech tests may unravel the deficits in part and thus leaving the evaluation incomplete as well as restricts offering/developing management strategies. While in some cases these central auditory tests could be the initial investigative procedures when auditory perception or complaints of hearing dysfunction are reported to first contact consultants. The audiologists with the Central Auditory Tests (CATs) on hand would probably the first person to suspect the lesion leading to neuroimaging investigations or to identify auditory processing disorders (Shivashankar et al., 2000, Shivashankar et al., 2013).
Research studies on auditory evoked potential (AEP) has given impetus to translational research to understand CAPD. AEPs such as; Middle latency response (MLR), Miss-Match Negativity (MMN) (Vanaja and Sandeep, 2007), Late Latency Response (LLR) (Sreevidya and Vanaja, 2003), P300 are being used as stand-alone or an adjunct to unfurl CAPD. However, these tests again are confined to major research or clinical institutions and are hardly done in private clinics. Also the required instrumentation set-up is not present at all places (Anuradha, 2011). It is possible to use speech and non-speech behavioural tests across any set-up as it requires only dual channel audiometer and a CD player. This requires commitment on the part of the audiologists to procure the available materials or develop materials as per the population requirement they serve.
Electrophysiological and functional neuroimaging including positron emission tomography (PET) have widened the scope of understanding the neurophysiological basis of CAPD. fMRI studies in the area of language has drawn the attention of researchers in the country across many academic institutions (Department of Science and Technology Cognitive Science initiatives). These have to be fully utilized by the audiologists to expand their research in the area of CAPD.
Several modules and training strategies have been developed to improve CAP skills (Maggu and Yathiraj, 2011, Shivashankar and Shashikala, 1998a, Shivashankar and Shashikala, 1998b, Yathiraj, 2006). Sometimes when auditory training activities based on usage of respective languages are not available, the audiologists may have to evolve techniques impromptu and advise accordingly. CAPD can exist as a unique entity as well as may be associated with conditions like ASD, ADHD, and auditory maturational delay. It needs clinical acumen to delineate the auditory processing deficits in them. This makes the current situation complex as it requires awareness amongst Child and Adolescent Psychiatrists, Pediatricians, Neurologists, Psychologists and Academicians in addition to Speech Pathologists and Audiologists themselves.
Audiologists in India have taken up the task of dealing with CAPD in children, adults and geriatrics through public education, interaction with allied medical professionals, developing age, language and culturally appropriate test and intervention materials and methods, but there is a long way to go.
Dr.N. Shivashankar is a professor and head of the Department of Speech Pathology and Audiology at the National Institute of Mental Health and Neurosciences in Bangalore, India. His research interests are in neuroaudiology. (Bio information from: http://nimhans.ac.in/users/drn-shivashankar)
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