Medicine:SCAN (auditory processing disorders)

SCAN, a screening test in audiology, was the first standardized test battery in the English language used for the assessment of central auditory processing disorders.   The purposes of SCAN were to determine possible central auditory nervous system (CANS) disorders, identify auditory processing problems, and identify children who may benefit from treatment.  Additionally, the purposes were to enable a clinician to identify the social and vocational needs of individuals and provide information about functional disorders of communication.

Several tests compose the SCAN Test batteries. They include tests of hearing functions related to the subject’s ability to understand speech that has been acoustically degraded in various ways.  The first version of the test  included low-pass filtered monosyllable words, auditory figure-ground testing, and a dichotic competing words test.  The  filtered words (FW) test is used to assess auditory closure skills. The test consists of monosyllable words that are low-pass filtered at 750 Hz, meaning frequencies above 750 Hz are filtered out; a measure that is said  to measure auditory closure. Persons being tested are required to fill in the missing information and repeat the word that was presented.  The auditory figure ground (AFG) test with a signal to noise ratio (SNR) of +8 dB is used to assess the individual’s ability to process speech in the presence of speech-babble background noise.  Competing words (CW) tests present dichotic words that assess the subject’s auditory pathway development, maturation of the auditory system, hemispheric function, and the presence of central pathway lesions.  In the competing words test, words are presented simultaneously, one to each ear.

SCAN-A and SCAN-C are extensions of SCAN tailored for use with adolescents and adult and children, respectfully. They were published with new test instructions and a revision of the competing words test. These test batteries consist of four tests of auditory processing including filtered words (FW), auditory figure ground (AFC), competing words (CW), and competing sentences (CS). A revised method of calculating the composite standard score gave equal weighting to each sub-test.  Normative data for SCAN-C was obtained on 650 children age five years zero months, to eleven years, eleven months.  The SCAN tests were among the main categories of tests suggested by the Task Force on Central Auditory Processing Consensus Development of the American Speech‐Language‐Hearing Association (ASHA) in 1996.

The latest revision of the SCAN battery is SCAN3 with versions available for children (SCAN3:C) and adults (SCAN3:A).  SCAN:3 is both a screening and a diagnostic test. The test battery contains three screening measures that can be used to determine if the entire battery should be administered. If a person fails the screening test, or if there is a referral for diagnostic testing, then the examiner can proceed with the diagnostic portion of the test.  The screening measures include a gap detection test, an auditory figure ground test at +8dB S/N ratio, and a free recall dichotic word test.  The criterion referenced norms provide cut-off scores for pass or fail of the screening measures.  The diagnostic tests include the same four tests used previously in the SCAN-C and SCAN-A tests in developing the composite score including filtered words, auditory figure ground, dichotic words under directed ear listening conditions, and competing sentences. There are optional tests available to investigate responses to time-compressed speech, and auditory-figure ground abilities at other speech to noise ratios.  The SCAN:3 diagnostic tests include all of the behavioral measures recommended in the Guidelines for the Diagnosis, Treatment, and Management of children and adults with central auditory processing disorder published in 2010 by the American Academy of Audiology [1].  

The SCAN-3:C and SCAN-3:A test batteries include nine co-normed tests including:

• Filtered Words, Auditory

• Figure–Ground: 0 dB signal-to-noise ratio,

• Auditory Figure–Ground: +8 dB signal-to-noise ratio,

• Auditory Figure–Ground: +12 dB signal-to-noise ratio,

• Competing Words–Free Recall,

• Competing Words–Directed Ear,

• Competing Sentences,

• Gap Detection, and

• Time Compressed Sentences Screening Tests.  

SCAN-3 C was designed for  Children 5:0–12:11 years and SCAN-3: A for individuals 13:0-50  years.  The time needed for completion of the screening tests is  10–15 minutes and the diagnostic tests 30–45 minutes.   Administration directions and test stimuli are presented via CD and scored by paper-and-pencil.  According to the instruction manual the test administration is flexible in that it may be administered through an audiometer at 50 dB HL or a portable CD player at the subject’s most comfortable listening level (MCL).  Interpretation of the results is done using published screening norm-based criterion referenced scores and diagnostic tests using scaled scores, percentile ranks, and ear advantage scores for all tests except Gap Detection.

Normative data used to develop SCAN-3 norms was obtained from a sample of 775 examinees. There were 525 children in the SCAN-3: C sample and 250 adolescents and adults in the SCAN-3: A sample.  The standardization edition of SCAN-3 was administered by 105 speech-language pathologists, and audiologists and school psychologists in 32 states.  The average reliability coefficients of the Auditory Processing Composite (APC) were .91 for the Children version and .93 for the Adolescents & Adult version.  Test-retest stability was  .77 for SCAN–3: C and .78 for SCAN–3: A.  Interscorer agreement for both tests was .98.  Evidence of validity in the Examiner’s Manual includes evidence based on test content, response processes, internal structure, and special group studies of 40 children, ages 5–12 diagnosed with Auditory Processing Disorder (APD) was completed as part of the validation research for SCAN–3: C. A total of 61 adolescents and adults diagnosed with APD were tested to provide evidence of validity for SCAN–3: A.  Each child in the APD group was matched to a control subject from the standardization sample based on age, parent education level, and race/ethnicity. Both studies provide evidence that SCAN-3 is a valid tool for identifying individuals with auditory processing disorders.  The SCAN-3C has been reported to be the most commonly used auditory processing test battery in the SCAN batteries.

The subject’s first (native) language, intelligence level, and attention span can affect the SCAN test results and should be taken into account.  Subjects for whom English is a second language may score lower than if the test was conducted in their first language.  Even subjects for whom English is a first language may yield a low score due to differences in accented speech, e.g. British accented English versus American accented English. Subjects with low intellectual ability may score at the level of their ability, but lower than the published norms for age.  Presentation level of the test stimuli can affect results. A hearing test should be administered prior to giving the SCAN battery to rule out hearing loss and/or asymmetry of hearing in the two ears.  The test is not designed to be administered to persons with hearing loss.  To do so may contaminate interpretation of results due to distortion of the speech signal caused by the hearing impairment.  Individuals with of attention deficit with or without hyperactivity may have difficulty completing the SCAN battery in one sitting. 

See Also

• Audiology
• Auditory Processing Disorders
• Speech Perception

External Links

American Academy of Audiology Clinical Practice Guidelines; Guidelines for the Diagnosis, Treatment and Management of Children and Adults with Central Auditory Processing Disorder, 2010.

de Wit, E., Visser-Bochane, M. I., et al. (2016). Characteristics of Auditory Processing Disorders: A Systematic Review. Journal of Speech, Language, and Hearing Research, 59(2), 384-413.[2]