Assessment of Central Auditory Processing Disorder (CAPD): Jerger and Musiek suggested Minimal Test Battery for CAPD includes Screening Tests, Behavioral Tests and Electrophysiological Tests.

Minimal Test Battery

Jerger and Musiek (2000) discussed a possible test battery that would include both behavioral and electrophysiological testing. The authors suggested this battery as a minimum:

• Immittance audiometry (tympanometry and acoustic reflex threshold testing) to ascertain the status of the middle ear as well as auditory neuropathy differential diagnosis
• Otoacoustic emissions to diagnose inner ear problems
• Auditory brainstem and middle latency evoked responses to assess brainstem and cortical level integrity
• Puretone audiometry to evaluate the integrity of the peripheral hearing system
• Performance-intensity functions for word recognition ability
• A dichotic task consisting of dichotic words, dichotic digits, or dichotic sentences (assessing the communication between hemispheres)
• Duration pattern and a temporal gap detection test to assess temporal processing aspects of CAPD

Screening for CAPD

CAP screening assesses the possibility of existence of a CAPD and, in turn, can lead to possible referral for a comprehensive CAPD evaluation. Psychologists and speech-language pathologists are two professional groups that would likely screen for CAP on a routine basis. For CAPD Screening there are many Questionnaires and Screening Tests are available.

Behavioral Tests for CAPD

The Behavioral Tests for CAPD is divided into 4 parts:

1. Monaural Low Redundancy Speech Tests
2. Dichotic Speech Tests
3. Temporal Patterning Tests
4. Binaural Interaction Tests

Monaural Low Redundancy Speech Tests

Monaural low redundancy speech tests divided into two part Spectral Degradation and Temporal Degradation.

Spectral Degradation

• Low pass filtered Speech Test – Brainstem/cortical lesions
• Speech Recognition in Noise Test – Brainstem to cortex

Temporal Degradation

• Time Compressed Speech Test – Primary auditory cortex

Dichotic Speech Tests

Dichotic Speech Tests are based on two types Binaural Integration/Summation and Binaural Sepration

Binaural Integration

• Dichotic Digits Test (Kimura, 1961 a) – Brainstem/cortical/corpus callosum
• Dichotic Consonant-Vowel Test (ShankWeiler, & Studdert Kennedy, 1967) – Cortical
• Staggered Spondaic Word Test (Katz, 1962) – Brainstem/cortical/corpus callosum
• Dichotic Sentence Identification – Brainstem/cortical
• Dichotic Rhyme Test (WexLer & Halwers, 1983) – Interhemispheric

Binaural Seperation

• Competing Sentence Test (Willeford, 1968) – Language processing
• Synthetic Sentence Identification with Contra Lateral Competing Message (Jerger, 1970) – Cortical vs. brainstem
• Pediatric Speech Intelligibility (PSI) Test (Jerger & Jerger, 1984) – Cortical vs. brainstem

Temporal Patterning Tests

Temporal Patterning tests are based on Temporal processing: Temporal Ordering, Temporal Resolution, Temporal Masking

Temporal Ordering

• Pitch Pattern Sequence Test (PPST) (Pinheiro and Ptacek in 1971) – Cerebral hemisphere lesions
• Duration Pattern Test (Mustek and colleagues in 1990) – Cerebral hemisphere lesions

Temporal Resolution

• Random Gap Detection Test – Left temporal/cortical
• Gaps-in-Noise – Interhemispheric transfer
• Frequency Pattern Test (FPT) – Cerebral hemisphere lesions

Binaural Interaction Tests

Binaural Interaction Tests are based on Binaural Integration or Binaural Summation

• Binaural Fusion Test (Matzker 1959; Ivey 1969) – Low brainstem
• Masking Level Difference Test (Hirish 1948 ; Licklider 1948 ; Durlach 1972) – Low brainstem
• Rapid Alternating Speech Test (Willeford 1976) – ?Low or high brainstem

Electrophysiological Tests for CAPD

• Immittance audiometry (tympanometry and acoustic reflex threshold testing) to ascertain the status of the middle ear as well as auditory neuropathy differential diagnosis
• Otoacoustic emissions to diagnose inner ear problems. Muchnik etal(2004) measured TEOAE  with contralateral suppression. This is interpreted to suggest the possible presence of reduced auditory inhibitory function that could have a deleterious effect on ability to hear in presence of background noise. Inrerestingly higher TEOAE amplitudes were observed in APD group, which authors describe as well to reduced MOC influence on OHCs.
• Auditory Brainstem Response (ABR) : Hall (1992) described case reports of children with APD and normal ABR findings
• Auditory Middle Latency Response (AMLR) are abnormal most often ie, in approximately 40 % of the APD patients (Hall & Mueller , (1997).
• Auditory Late Latency Response (ALLR):
  • P1, P2 and and N1 components were analysed by Purdy , Kelly & Davies (2002). The P2 component of ALR was not consistently recorded and typically small in amplitude. There were significant group differences for ALR P1 (shorter latency in APD group) and the N1 component (smaller amplitude in APD group).
  • Schulte- Korne et al(1998) reported a difference between dyslexic and APD group in MMN ( smaller amplitude) evoked by speech stimuli, but not for tonal stimuli.
  • Purdy et al (2002) reported significantly prolonged latency with smaller amplitudes of the P300 response in with suspicion of APD.

References:

⇒ Essentials of Audiology – Stanley A. Gelfand, PhD (Book)
⇒ Handbook of Clinical Audiology – JACK KATZ, Ph.D. (Book)
⇒ Handbook of Central Auditory Processing Disorder Volume I (Auditory Neuroscience and Diagnosis) – Frank E. Musiek, Gail D. Chermak (Book)

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Assessment of Central Auditory Processing Disorder (CAPD)