El Síndrome de Procesamiento Auditivo Central (SPAC): nuevas perspectivas hacia la evaluación de los síntomas

The study of children and adults with hearing and listening comprehension deficits that is not justified by a deficit hearing profile on the audiogram, has aroused the interest of numerous research groups in recent decades, the result of which has been the definition and compilation of evidence regarding the evaluation of Central Auditory Processing Syndrome (CAPS). In this article, a historical tour was made through the definition of the syndrome and the different instruments currently used for its diagnosis.


Introduction
The different theoretical and practical approaches in the investigation and definition of Central Auditory Processing Syndrome (CAPS) are detailed. The first definitions came from Katz, who proposes the first definition of auditory processing syndrome or disorder as "what we do with what we hear" (Katz, Stecker & Henderson, 1992, p. 5). This definition, although it seems simplistic, hides the first solid theoretical approach. For them, auditory processing involves more than the central system and auditory perception; for this reason, they recommend the use of the term central auditory processing defined as "The serial and parallel processing of the auditory system responsible for hearing care, detection and identification of auditory signals, decoding of the neural message, as well as the storage and retrieval of information related to hearing" (Katz et al., 1992, p. 41). From this definition, the existence of normal hearing and intelligence in subjects with CAPS is inferred. In 2005, the American Speech-Language-Hearing Association (ASHA) described the auditory skills necessary to assess to indicate the presence of CAPS, these are: localization and lateralization, auditory discrimination, temporal aspects of hearing (masking, resolution, integration and temporal ordering) and auditory performance with competitive acoustic signals. In 2010, the American Academy of Audiology (AAA) proposed that the CAPS makes reference to the difficulties found in the perceptual processing of auditory information in the central nervous system and the neurobiological activity underlying this processing that gives rise to electrophysiological auditory potentials (Goll, Crutch & Warren, 2010). The British Society of Audiology (BSA) understands that CAPS is characterized by a poor perception of speech and non-verbal sounds with a neurological origin (2011). Difficulties in the perception and understanding of speech can have several causes, although it does not justify the existence of an auditory processing disorder. The BSA establishes three CAPS classification categories: evolutionary, acquired, and secondary . In 2012, the working group of the Canadian Interorganizational Steering Group for Speech Language Pathology and Audiology (CISFSLPA) published a conceptualization of CAPS from a neurobiological perspective, requiring the use of instruments for its diagnosis (Bellis & Bellis, 2015). Despite the prevalence of the problem, around 2-7% of the population (Bellis & Bellis, 2015), a systematic approach to the diagnosis and rehabilitation of CAPS in children has only begun to be relevant in the last 40 years. It is important to recognize that CAPS is a heterogeneous disorder and the impact of the deficit on functional abilities is unique in each subject. Therefore, the diagnosis and the intervention process must be based on the single case paradigm . This research work is intended to show the different tests necessary to perform an assessment of the CAPS from an integrative perspective, taking into account the clinical utility and the versatility of its use in the consultation.

Method
Articles in Spanish and English published in the databases of different search engines for scientific articles such as Scopus, Researchgate or ScienceDirect were reviewed. The articles were not limited to the date of publication because the search was made from the first publications where the word CAPS or CAPD appeared up to the present. In the databases, the keywords "auditory disorder" "evaluation of auditory disorder" or "auditory processing evaluation" were used. The criteria used for the selection of articles was that research on CAPS assessment instruments should appear in their abstract. Articles and publications of texts that offered data on the reliability and validity of the test were included, although since the CAPS assessment itself implies the single case paradigm; data from assessment instruments that lack these data are also provided.

Results
In the bibliographic search, it was found that the first lines of research that sought the definition of the CAPS were directed towards impaired hearing processes and their evaluation. For this reason, in addition to the specific auditory processing tests, data from the medical history, audiometric evaluation and neuropsychological functions were collected (American Speech Language Hearing Association [ASHA], 2005a; 2005b). One of the first references is from 1954, by Myklebust who emphasized the need to name perceptual disorders that could not be attributed to a peripheral hearing loss. In 1956, Berry and Eisenson also identified children with these types of perceptual difficulties. The first reports of clinical evaluation of hearing dysfunction appeared in 1963 in an article by Bocca and Calearo. These rudimentary tests aroused interest in functional tests that allowed identifying a lesion in a specific area of the central nervous system from auditory stimuli. The first test widely used as a clinical measure of auditory processing, although it only evaluates the auditory discrimination process, was developed in 1958 by Wepman and Reynolds, under the name Wepman Auditory Discrimination Test. Along the same initial line of evaluation, in 1959, Matzker described the Binaural Fusion test, Katz designed the SSW Test in 1962 and Speaks and Jerger published the Synthetic Phrase Identification Test in 1965. The lack of diagnostic sensitivity and specificity of these tests made them stop being used, although they are considered the beginning of the clinical research (Jerger, 1987).
In the 1970s, the first specific tests for children began to be developed, the Flowers Costello Test of Central Auditory Skills (Flowers, Costello & Small, 1970). At that time, the Goldman Fristoe Woodcock Hearing Discrimination Test was also published (Goldman, Fristoe & Woodcock, 1970). Katz and Fletcher (1998) developed the Phonemic Synthesis Test in 1972 and  developed the Colorado Test Battery. The Willeford Test Battery  was a first attempt to develop a complete battery of tests and later Keith (2000b) presented the SCAN-C Test for Auditory Processing Disorders in Children. At present, it is proposed that the evaluation of the CAPS is articulated in three different lines: the psychophysical evaluation, the psychometric or behavioral evaluation and the electrophysiological evaluation .
Psychophysical evaluation of central auditory processing Dichotic listening. Both separation and binaural integration are evaluated (Ianiszewski, Urrutia, García, Quintana, & Peña, 2016;). An example is the SCAN battery (Keith, 2000b), the SSI-CCM that has been adapted to Spanish (Benitez & Speaks, 1968) and the SSW tests (Katz, 1962). Low redundancy monaural speech (auditory closure). In this category, tests of speech in noise, competitive messages, filtered speech and compressed speech are found . Binaural interaction test. It refers to the tasks where the information perceived by both ears must interact . Stimulus temporal ordering or sequencing tests. There are two tests, the Pitch Pattern Sequence  and the Frequency Pattern Test . Temporal resolution tests. The Random Gap Detection test (Keith, 2000a) and the Gaps in Noise test .

Psychometric assessment of central auditory processing
Analysis of Language Delay (A-RE-L). It can assess the state and evolution of the linguistic competence of children between 3 and 6 years old . It does not collect statistical data. Battery of Verbal Exploration for Learning Disorders (BEVTA). Bravo & Pinto (2007) made this test for children between 7 and 12 years old. It determines the relationship between reception and immediate retention of verbal information. It has an internal consistency between 0.30 and 0.50, reliability between 0.72 and 0.82, and validity of 0.09.
Objective and Criterial Language Battery -Revised (BLOC-R). This test assesses semantics, morphosyntax and pragmatics of the language of children between 5 and 14 years old . This test has an internal consistency of 0.88, reliability between 0.97 and 0.98 and the validity of the 5 factors explains 60.89% of the variance. CEG. Comprehension Test of Grammar Structures.  designed this test that determines the level of vocabulary comprehension of children from 4 to 11 years old. The internal consistency is 0.90, the reliability between 0.779 and 0.866 and the criterion validity is 0.809. Children's Auditory Performance Scale (CHAPPS). It is a scale designed by  for children between 7 and 8.11 years old and it provides information on the variations in auditory function according to environmental conditions. The reliability data ranges between 0.67 and 0.88. Basic Concepts for Early Childhood and Primary Education (CONCEBAS I and II). It evaluates basic concepts for children between 4 and 8 years old (García & Yuste, 2007). It presents a reliability between 0.79-0.86. DST-J. Test for the detection of dyslexia in children. (Fawcett & Nicholson, 2012). It is applied between 6.6 and 11.6 years in order to detect symptoms of dyslexia and be able to carry out the differential diagnosis of CAPS. This test has a reliability of 0.88 and a validity of 0.90. The development of morphosyntax in the child (TSA). This test for children between 3 and 7 years old assesses stages of syntactic construction (Aguado, 2014). It does not have statistics. The Visual and Auditory Digit Memory Test (VADS). The purpose of the test is to assess the capacity for sensory integration and immediate visual and auditory memory for children from 5.6 to 12 years old. Reliability is between 0.74 and 0.92 (Koppitz, 1981). Reynell scale of language development III. This test aims to determine the level of comprehensive and expressive language of children between 1.6 and 7 years old. The test has a reliability between 0.75 and 0.83 and validity between 0.68 and 0.75 (Edwards et al., 1997) Vocabulary estimation (EVOCA). This test by  assesses the evocation and expression of vocabulary in children between 8 and 16 years old. It does not have statistics. Evaluation of Auditory and Phonological Discrimination (EDAF). This test aims to detect possible alterations in hearing discrimination in children between 2.8 and 7.4 years old. The reliability ranges between 0.24 and 0.84 and the construct validity is 0.01 (Brancal, Alcantud, Ferrer & Quiroga, 2007). Evaluation of Phonological Knowledge of Syllabic and Phonemic type (PECO). . It assesses the level of syllabic and phonemic phonological knowledge in 5-year-old children. It offers a reliability of 0.801.
Oral language assessment. In this test, a language assessment is performed in children between 4 and 8 years old. It has a validity of 0.80 and a reliability of 0.91 . Phonological evaluation of children's speech. This test performs a phonetic-phonological profile for children between 3 and 7 years old. It offers reliability data between 0.98 and 0.99 (Bosch, 2004). MACARTHUR communication development inventories. With this test,  value the acquisition of language in children between 8 and 30 months. It presents an internal consistency between 0.70 and 0.99, a reliability between 0.83 and 0.97 and a validity between 0.66 and 0.96. Listening Inventory for Education-Revised (LIFE-R) This scale designed by Anderson, Smaldino and Spangler (2012) is a self-report for children from 8 years old and collects information on noisy situations in the classroom. It does not collect statistics. Joint disorders, exploration, prevention, diagnosis and treatment (Borregón, 2010). This test assesses the child's phonetic and phonological disorders and makes it possible to differentiate the affected phonemes in the child. It does not collect statistics. Initial Luria. Neuropsychological evaluation in preschool age. It studies four neuropsychological functions in children between 4 and 6 years old: language, memory, speed processing and motor skills. Besides, it assesses laterality. The internal consistency is 0.861 . Test Aptitudes in Early Childhood Education (AEI). Developed by De la Cruz (1999), it assesses the aptitudes of children in 2nd and 3rd grade of early childhood education. Reliability is between 0.68 and 0.90 and validity between 0.10 and 0.65. Phoneme Articulation Test (PAF). Assessment of dyslalia. It evaluates aspects of language articulation in children between 5 and 8 years old . It does not offer statistics. Forward and Inverse Digits Test of the WISC-IV, Wechsler Intelligence Scale for Children. The WISC-IV Digit Test  essentially measures auditory short-term memory, the ability to follow a sequence in children ages 6 to 16. The reliability is between 0.80 and 0.89 and the construct validity is between 0.90 and 0.98. Discrimination test from the Speech Delay Analysis (AREHA) Test. The objective is to assess the phonological contrasts of the language in children between 3 and 6 years old. (Aguilar & Serra, 2003). It does not offer statistical data. Auditory perceptual discrimination test of the Comprehensive and Expressive Vocabulary Assessment (ELCE). For children between 2.6 and 9 years old; perception of sounds, rhythm, discrimination of sounds and phonetic discrimination are assessed . It does not offer statistics. General language test of the WPPSI-III, Wechsler Intelligence Scale for preschool and primary levels (Wechs-ler, 2004). It assesses the ability to understand verbal instructions and auditory discrimination in children from 2.6 to 7.3 years old. It has an internal consistency of 0.80-0.95, reliability of 0.90-0.98, and validity from 0.68 to 0.92. Navarra Oral Language Test (PLON-R). It evaluates the language of a child between 2 and 6 years old (Aguinaga, Armentia, Fraile, Olangua & Uriz, 2004). The components of the test assess form, content and use of language. It has an internal consistency between 0.66 and 0.699, and reliability between 0.745 and 0.774. Verbal memory test of words, phrases and stories of the McCarthy Scales of skills and psychomotor skills for children. This test  is applied to children from 2.6 to 8.6 years old. Immediate memory capacity is assessed. It presents an internal consistency between 0.77 and 0.8 and a validity of 0.81. Evaluation Battery of Necessary Skills for Learning to Read and Write (BENHALE). This test contains two scales, the immediate logical auditory memory test and the auditory perception and discrimination test for children aged 5 and 6. These tests present reliability of 0.71 and 0.79 and a validity of 0.75 . Auditory perception assessment test. It is an instrument that assesses the auditory perception of noises and sounds of language for children between 3.6 and 7 years old (Gotzens & Marro, 2001). This test does not provide statistical data. Immediate Auditory Memory Test (MAI). This test developed by Cordero (1997) for children between 9 and 13 years old assesses logical memory, numerical memory or associative memory. Its reliability is 0.79; and its validity, 0.20. Induced phonological register. This test by  includes among one of its tests the registration of the spontaneous and directed articulation of the words showed to children between 3 and 7 years old. It does not offer statistical data. Boehm Basic Concepts Test -3. It assesses the understanding of basic concepts in children between 4 and 7 years old (Boehm, 2012). Its reliability is 0.80-0.93; and its validity, 0.50-0.84. Metalinguistic Skills Test (THM). It evaluates the level of metalinguistic development in children between 5 and 6 years old (Gómez, Valero, Buades & Pérez, 1995). This test has an internal consistency of 0.81; reliability, 0.95; and validity, 0.83. Fisher hearing problems test. Designed by Fisher in 1976, it provides information on the functioning of the auditory behavior of children between the ages of 5 and 11.11. The test does not offer statistical data. Vocabulary in Pictures Test (TEVI). It measures the comprehension of orally administered vocabulary in children between 2.6 and 17 years old (Echeverría, Herrera & Vega, 1987). It presents an internal consistency of 0.91-0.95 and a reliability of 0.96. PEABODY picture vocabulary test. It assesses comprehensive vocabulary in children from 2 years old (Dunn & Pereda Marín, 1986). It has an internal consistency of 0.96, reliability of 0.77, and validity of 0.88. Illinois Test of Psycholinguistic Aptitudes (ITPA). This test (Kirk, McCarthy & Kirk, 1999) evaluates children between 2.5 and 10.5 years old. The ITPA test, in a 1985 study by Sineiro, Nogueira, Fernández and Gómez, collects data on internal consistency (0.89 and 0.92) and reliability (0.62 and 0.85). The subtests of this test that assess CAPS symptoms are the following: a) listening comprehension test, b) auditory association test, c) auditory integration test, d) sound gathering test, and e) auditory sequential memory.
Electrophysiological evaluation of central auditory processing The BIC. It is an electrophysiological test used to evaluate the central auditory competencies of interhemispheric integration. It is used as an objective measure of binaural interaction (Delb, Strauss, Hohenberg, & Plinkert, 2003). The P300. It is an endogenous evoked potential caused by the cognitive processing of sensory stimuli. The P3a reflects attention processes originated in the frontal lobe and the P3b is related to working memory due to the activity in the central auditory regions of the cortical circuit . The PEALM. These types of evoked potentials occur between 10 and 80 ms. after the starting of the sound stimulus. Some studies indicate that it can serve as an indicator in the study of the auditory pathway dysfunction. (Cañete, 2006;. The PEATC. They represent the bioelectric activity generated in the central nervous auditory system at the level of the brain stem after the presentation of an acoustic stimulus. They are registered between 1 and 15 milliseconds after the auditory stimulus. This activity is recorded by positive and negative voltage fluctuations visible in the EEG (Cañete, 2006;. The MMN. It is another electrophysiological measure of the CAPS. It is observed when the system identifies a change in sound or speech and it can occur without the subject having to respond to this change. The neuronal disparity mechanism that generates MMN is located in the supratemporal auditory cortex. .

Discussion
The studies that evaluate the CAPS assessment instruments are scarce and focused on a single instrument. Studies with instruments of all the modalities presented and with a large sample population are needed to be able to offer a battery of tests with quality statistical references (DeBonis, 2015). Future guidelines are aimed at a combination of instruments in the three current lines: psychophysical, psychometric and electrophysiological with scales for children and new tools that allow obtaining data on auditory processing in children at different ages.