Test battery of AP and cognition

Participants were tested during a 1-hour session using five non-speech measures of AP, one speech-in-noise test, and three measures of nonverbal cognitive skills and short-term memory from the previously described IMAP protocol.²⁶

The test battery was presented using laptop computers running customized software (MRC Institute of Hearing Research, System for Testing Auditory Responses (IHR-STAR), Nottingham, UK)²⁷ that generated test stimuli in a randomized order of administration for the AP tests, and ensured that test protocols were followed.²⁶ All auditory stimuli were presented through Sennheiser HD25 headphones (Wedemark, Germany). AP and cognitive tests were interleaved. The tester provided positive reinforcement, in the form of verbal praise and stickers, as needed during each session in order to maintain motivation for the child.

To evaluate temporal processing we used backward masking without a temporal gap between the target tone and the masker (BM), backward masking with a 50-ms temporal gap between the target tone and masker (BM50), and frequency discrimination (FD) (Figures 1a, b and e). To assess spectral processing, we used simultaneous masking without (SM) and with a spectral notch (SMN) surrounding the target frequency (Figures 1c and d). The test paradigm employed a 3-alternative, 3-interval forced choice adaptive staircase (3-down, 1-up) strategy,²⁸ by which target stimuli varied based on correct and incorrect responses of the child according to methods previously described.^{19, 20, 26}

Schematic diagrams depicting a single trial, comprising three presentation intervals, for each of the individual auditory processing tests in the IMAP test battery. The task for each trial is to detect the interval containing the target tone. (a–d) The three boxes designate successive sound presentation intervals separated by standard interstimulus intervals (ISI). The heavy horizontal bar represents the 20-msec target tone (arrow) and shading represents frequency bands of masking. (a) Backward masking (masker occurs immediately after the target tone) without a temporal gap between the masker and target tone (BM). (b) Backward masking with a 50-msec gap between the masker and target tone (BM50). (c) Simultaneous masking (masker and target tone occur at the same time) (SM). (d) Simultaneous masking with a 400 Hz spectral notch in the masker (SMN). (e) Frequency discrimination (FD); the heavy horizontal bar represents a 200-msec tone that occurs in each of the presentation intervals; two of the tones are at 1000 Hz (standard) and the third is a target tone presented at a higher frequency. In all of these examples (a–e) the presentation interval containing the target stimulus is shown in the middle, but the target could occur randomly at any interval. msec, millisecond; Hz, Hertz.

The speech-in-noise test involved repetition of recorded VCV nonsense syllables in 3-band, single-male-talker-weighted, idealized speech-modulated noise⁹ using matched procedures to the non-speech AP tests.

Cognitive tests comprised standardized measures of nonverbal reasoning and included nonverbal IQ (NVIQ) from the Matrices Reasoning subtest of the Wechsler Abbreviated Scale of Intelligence,²⁹ working memory for forward and backward digit span, Wechsler Intelligence Scale for Children – Fourth Edition,³⁰ and phonological processing and memory measured by nonsense word repetition (NWR) subtest of the Developmental Neuropsychological Assessment.³¹

While the twins were participating in the study tests, an accompanying parent completed the CCC-2 (US Edition) a standardized 70-item questionnaire used to assess a child's communication and social interaction abilities.²¹ Parents also completed a brief questionnaire regarding their child's hearing, developmental, and otologic history. The same parent completed questionnaires for both twins and the full set of questionnaires was completed for one child at a time.