Pure tone audiometry was performed
using the GSI Audiostar Pro (Grason Stadler, Eden Prairie, MN) with ER3A
insert headphones in a sound booth following a modified Hughson-Westlake procedure
(Carhart & Jerger, 1959). Pure tone air thresholds were obtained at 250, 500,
750, 1000, 1500, 2000, 3000, 4000, and 8000 Hz. A descending-ascending step
size of 10dB was used followed by refining 4dB steps,
and a final 2dB step. Mean hearing level was calculated using the arithmetic
mean of the pure tone thresholds at 500, 1000, 2000, and 4000 Hz. The TEN (HL) was
performed at 500, 750, 1000, 1500, 2000, 3000, and 4000 Hz with the test tone and TEN-masking generated from the
audiometer, as described by Moore et al. (2004).
TEN level for each frequency was determined by the absolute hearing
threshold. For frequencies with an absolute threshold equal to or below 60dB HL, the TEN level was set to 70dB HL. If the
absolute threshold exceeded 60dB HL, the TEN level was set to 10dB above the
audiometric threshold up to a maximum TEN level of 90dB HL. TEN level for
frequencies exceeding 90dB HL or when the participant indicated they could not
tolerate the loudness the TEN level was set equal to the audiometric threshold.
A threshold search was then conducted using a final 2dB step size. All
measurements were performed within a single session.
At each frequency, the absolute
threshold was compared to the TEN-masked threshold to determine if a dead
region was detected using the criteria suggested by Moore et al. (2004). If the
TEN-masked threshold was ?10dB above the TEN level and ?10dB above the absolute
threshold that frequency is assumed to be a dead region. A dead region is
assumed to be absent if the TEN-masked threshold was <10dB above the TEN level and ?10dB above the absolute threshold. For frequencies when the masked threshold was <10dB above the absolute threshold and the TEN level could not be increased further the dead region was considered inconclusive.