I work in a diagnostic clinic and a hearing aid clinic, and every day I find myself challenged to do a thorough evaluation of hearing abilities and to make recommendations for hearing aids or other rehabilitation. The audiogram has historically consisted of pure-tone threshold testing to determine sensitivity across frequencies using pure tones, frequency modulated tones, or fresh noise. Frequencies typically tested are 250 Hz to 8,000 Hz, with some additional higher frequencies used when monitoring for hearing sensitivity changes above 8,000 Hz, as seen in exposure to ototoxic substances. We use air- and bone-conducted signals to diagnose and differentiate conductive, sensorineural, and mixed hearing loss.
Speech testing often consists of speech reception thresholds and word recognition testing and measuring thresholds at different frequencies. The expectation is that the speech reception threshold will correspond to the softest threshold or the softest average threshold for tonal stimuli. Word recognition testing is typically done at a specified sensation level relative to the speech reception threshold or at a chosen hearing level. Presentation level depends on the test's purpose. Testing to measure the best performance and amplification would typically be completed at a specific sensation level above the speech reception threshold.
Presentation level may also be completed at a specified sensation level in reference to a threshold at 2,000 Hz because audibility of the band centered around 2,000 Hz significantly contributes to performance and should be considered. (American National Standards Institute, 2007. Methods for the Calculation of the Speech Intelligibility Index; see FastLinks; J Am Acad Audiol 2009;20:381.) Word recognition testing may also be completed at a set hearing level associated with conversational speech level, or hearing level in decibels, that corresponds to an average conversational speech level. (Pearson K, Bennett R, Fidell S, 1977. Speech Levels in Various Environments [Report No. EPA-600/1-77-025] Environmental Protection Agency.)
Unfortunately, threshold and word recognition testing do not always yield adequate information to predict hearing ability in the real world. I frequently see patients in the clinic who complain of difficulty hearing in background noise or in other difficult listening situations, such as in rapid speech, who may have normal hearing thresholds. I also see performance differences in those with hearing loss who have comparable thresholds across frequencies.
Psychoacoustic abilities have been shown to have a significant effect on hearing ability and speech understanding in a variety of difficult situations. Many studies of psychoacoustic abilities, such as temporal resolution, have included gap detection, amplitude modulation detection, and masking paradigms. The procedures have often been designed for use in a laboratory-like setting with testing that takes significant time for each individual. Unfortunately, in clinical audiology, time management should be considered when evaluating hearing. (Int J Audiol 2012;51:3.) We often do not have the time or equipment to add patients' psychoacoustic measures or physiologic capabilities to the test battery.
An Adaptive Clinical Test of Temporal Resolution: Age Effects
Lister JJ, Roberts RA, Lister FL Int J Audiol 2011;50:367
An Adaptive Clinical Test of Temporal Resolution: Within-Channel and Across-Channel Gap Detection
Lister J, Roberts R, et al Int J Audiol 2011;50:375
A number of clinical tests have been developed in recent years to make measuring some psychoacoustic abilities or physiologic functions more clinically feasible. The Random Gap Detection Test was developed in 2000 and the Gaps-In-Noise test in 2005. (Ear Hear 2005;26:608.) Two newer temporal resolution tests include the temporal fine structure test, the temporal fine structure-low frequency test, and the adaptive clinical test of temporal resolution (ATTR). (Int J Audiol 2009;48:161; Int J Audiol 2010;49:940; Am J Audiol 2006;15:133.)
The ATTR is a gap detection test administered by computer with a sound card. The ATTR can be completed using within-channel narrow-band noise or across-channel broad-band noise (pre- and postgap signal) using a narrow-band noise signal centered at one frequency with a second narrow-band noise centered at a higher or lower frequency. One of the benefits of using narrow-band noise is controlled audibility at each frequency. The ATTR is an adaptive psychophysical procedure, unlike most clinical tests, and uses a two-alternative, forced-choice paradigm in which the individual uses a computer mouse to select the signal that contains the gap.
A recent publication provided normative data for ATTR gap detection thresholds for narrow-band noise in within-channel and across-channel conditions in each ear of normal-hearing children (ages 7-12) and older adults (ages 50-84) with normal hearing sensitivity or hearing loss of varying degrees. (Int J Audiol 2011;50:367.) A 1,000-Hz or 2,000-Hz narrow-band noise marker was used for the within-channel and across-channel gap detection.
Results showed that the youngest children (ages 7-8) required wider gaps than the older children and adults. The older adults performed more poorly than the younger adults but better than the younger children (ages 7-10). Results also demonstrated that the gap detection thresholds in the across-channel conditions were significantly greater than those in the within-channel conditions. The study concluded that the ATTR can be used to assess temporal resolution ability in children and adults, and was sensitive to changes in temporal resolution ability across ages tested (7-84).
The second study of the ATTR investigated the effects of presentation level (80 dB sound pressure level or listener-selected level) and sound card (expensive vs. inexpensive). (Int J Audiol 2011;50:375.) Participants were young adults 20-37 with normal hearing sensitivity. Results suggested that the listener-selected presentation level and the sound card did not significantly affect the gap detection threshold. The authors suggested that the ATTR results could be used effectively in a clinical setting with a computer and sound card with the ATTR software.
The remaining challenge is implementing psychoacoustic or physiologic tests in the clinic with real patients. I am not suggesting that we eliminate pure-tone audiograms and speech audiometry, but we should add another 15 to 30 minutes to our test battery to make more appropriate recommendations after the test is over, given the inadequate time to do our job.
We will likely see new, more clinically feasible tests for clinicians and patients in terms of time, required equipment, and skill level as we continue to explore, determine, and define the skills and abilities of those with hearing loss. It is mandatory that audiologists try these new clinical tests to determine how accurately they predict performance on specific tasks and whether they correlate to clinical outcomes. We must attempt to do what we can to improve our capabilities and diagnose not just hearing sensitivity but auditory skills needed to function daily in the real world.
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