Perception Versus Evidence Comparisons Support Auditory Steady-State Response in Pediatric Hearing Evaluations Features
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Features  |   August 01, 2012
Perception Versus Evidence
Author Notes
  • Barbara Cone, PhD, CCC-A, is professor of speech, language, and hearing sciences at the University of Arizona, Tucson. Her research interests include human auditory system development and electrophysiology. She is an affiliate of Special Interest Groups 6, Hearing and Hearing Disorders: Research and Diagnostics; and 9, Hearing and Hearing Disorders in Childhood. Contact her at conewess@email.arizona.edu.
    Barbara Cone, PhD, CCC-A, is professor of speech, language, and hearing sciences at the University of Arizona, Tucson. Her research interests include human auditory system development and electrophysiology. She is an affiliate of Special Interest Groups 6, Hearing and Hearing Disorders: Research and Diagnostics; and 9, Hearing and Hearing Disorders in Childhood. Contact her at conewess@email.arizona.edu.×
Article Information
Hearing Disorders / Features
Features   |   August 01, 2012
Perception Versus Evidence
The ASHA Leader, August 2012, Vol. 17, 5-7. doi:10.1044/leader.FTR3.17102012.5
The ASHA Leader, August 2012, Vol. 17, 5-7. doi:10.1044/leader.FTR3.17102012.5
The perception that auditory steady-state response (ASSR) is “not quite there” for routine use in the evaluation of children’s hearing remains fairly widespread. But ASSR has been a staple of the electrophysiology literature devoted to “evoked response audiometry” for nearly 20 years, with more than 60 papers from the world literature published in the last decade. This research has established ASSR as a valid, reliable, and efficient tool for evaluating hearing loss in children (Cone & Dimitrijevic, 2009; Korczak et al., 2012; Picton, 2011; Rance, 2008).
Why does skepticism remain despite the voluminous research supporting ASSR’s effectiveness? To suggest possible answers to this question, we need to consider how ASSR was developed and recent prospective studies comparing it to auditory brainstem response (ABR).
ASSR Technologies
Initially, differences in testing methodology—along with competing marketing claims—may have caused some confusion and slowed the uptake of ASSR by clinicians. When ASSR instrumentation became available in the United States, there were two approaches: the single-frequency technique, implemented on the GSI-Audera, and the multiple-frequency (MASTER) technique provided first by BioLogic, and now also by Intelligent Hearing Systems (Smart ASSR), Interacoustics (Eclipse), and Vivosonic (Integrity).
The Audera was the outgrowth of University of Melbourne research investigating ASSR primarily as a means to evaluate infants and young children for cochlear implantation—that is, those with a high risk for moderate or greater sensorineural hearing loss (Rance et al., 1993; Rickards, 2008). In contrast, MASTER was part of a long commitment to “evoked response audiometry”—the accurate estimate of hearing status using electrophysiology. The University of Toronto group used an innovative stimulus method, in that up to four carrier frequencies could be presented simultaneously to each ear, dichotically, yielding ear- and frequency-specific thresholds in less time than it would take to test individually and sequentially (Picton, 2011; Picton et al., 2003).
An advantage of the Audera method is the sizable database of ASSR results obtained with this technology for infants and young children, including those with hearing loss (Rance & Briggs, 2002; Rance & Rickards, 2002; Rance et al., 1995, 2005; Rickards et al., 1994). A disadvantage of this particular method is that elevated threshold estimates may be obtained in tests completed without sedation, and in comparison to tests given with other instruments for which averaging times could be extended to achieve the reduction in myogenic and EEG noise necessary to resolve responses with low amplitudes and a poor response-to-noise ratio (Luts & Wouters, 2005).
A notable advantage of the MASTER technology—in addition to the time savings gained by simultaneously testing at several frequencies in both ears—includes the ability to average for longer periods of time, thus leading to lower (i.e., “better”) thresholds. Another advantage is that the stimulus and acquisition parameters have been based upon careful, lab-based, published experiments, albeit primarily in adults (John et al., 1998; 2001a, b; 2003; 2004) . Verification of its performance in infants and children with hearing loss has lagged, somewhat, in comparison to Audera.
Consumers (in this case, audiologists) wanted information showing how ASSR compared to ABR. Why adopt a new, unfamiliar technology, audiologists wondered, when click and tone-burst ABR (tb-ABR) were the standard of care and state of the art for electrophysiologic evaluation of infant hearing?
Audiologists asked for prospective, head-to-head comparisons of ASSR with ABR. Despite the paucity of funding for this type of research, we now have results from well-designed and well-executed prospective studies comparing ASSR to ABR.
ASSR Versus ABR
Johnson and Brown (2005) performed ABR and ASSR tests in adults with normal hearing, and in those with either flat or sloping sensorineural hearing losses. In those with normal hearing, there was a smaller difference between ABR and behavioral thresholds than for ASSR. This result was also true for those with flat sensorineural hearing losses. However, for those with sloping losses, ABR tended to underestimate the hearing loss, whereas ASSR did not. The investigators point out that the difference in size between the evoked potential threshold and behavioral threshold is not as important as the variability of that difference. There was less variability for ABR in those with normal hearing, but for those with flat hearing loss, variability measures were the same for ABR and ASSR. For those with sloping losses, there was less variability with ASSR.
It is necessary to consider underlying physiological mechanisms to appreciate why ASSR may show comparatively poorer response-to-noise ratios and threshold variability than the tb-ABR. Decrements in ABR amplitude and synchrony occur as stimulus rate is increased (Don et al., 1977), and these decrements are more evident in infants because of the immaturity of the brainstem auditory nervous system (Lasky et al., 1984; Rance & Tomlin, 2006). A true head-to-head comparison of ASSR with tb-ABR, with stimulus levels, envelopes, and rates equated, would likely show no differences in ABR vs. ASSR threshold. That being said, the differences between steady-state vs. transient ear stimulation of the cochlea and brain, combined with differences in the way the two potentials are detected and measured, may prove to be advantageous for ASSR.
Van Maanen and Stapells (2010) compared tb-ABR and ASSR thresholds in children with hearing loss. The multiple-frequency (MASTER) technique was used to obtain ASSRs. Results indicated that tb-ABR and ASSR thresholds were highly correlated (r=0.97). The authors concluded that “The results of...[the present study] show that the ASSR provides a reasonably accurate estimate of hearing threshold.” They cautioned, however, that further research of this type was needed to enlarge the evidence base of multiple-ASSR threshold results in infants and children with hearing loss.
ASSR Advantages
ASSR modulation rates—at 80 Hz or greater—can be advantageous, because in many cases it is possible to achieve a favorable response-to-noise ratio in a shorter amount of time than for slower rate tb-ABR. This advantage overcomes the disadvantage of the loss of response amplitude at a faster modulation rate (Burkard & McNerney, 2009). Another ASSR advantage is the ability to test simultaneously at multiple frequencies, resulting in more time-efficient protocols compared to single-frequency sequential techniques (Hatton & Stapells, 2011).
The response detection algorithms implemented with ASSR data acquisition and analysis software offer a clear advantage. These algorithms—based on statistical properties of response phase and/or spectral power at the modulation frequency—provide a means for automating both response detection and threshold searching. Accordingly, they provide a truly objective analysis of brain-evoked activity, whereas tb-ABR conventionally is performed with subjective analysis of waveforms, and may, therefore, be more dependent on the training and experience of the audiologist.
The group at the University of British Columbia, led by David Stapells, has cautioned that it is still necessary to expand the evidence base for ASSR, particularly in the area of definitively assessing air and bone-conducted thresholds. Conversely, a host of clinical research findings from labs around the world—including the University of British Columbia—provide regression formulas or ASSR-behavioral threshold correction factors to allow estimation of perceptual threshold on the basis of ASSR threshold (Cone & Dimitrijevic, 2009; Korczak et al., 2012). These formulas are based on findings in several hundred infants, children, and adults.
Evidence to Practice
As audiologists we employ evidence-based practice, and are therefore responsible for monitoring new developments in the literature (ASHA, 2004). The evidence base for using ASSR has expanded greatly since 2004. And although ASSR may not be sufficient as the sole measure of newborns’ and infants’ auditory status (JCIH, 2007), most would also agree that it would not be good practice to use click or tB-ABR as the sole measure of auditory status, either. Otoacoustic emissions, tympanometry, acoustic reflex thresholds, and, when possible, behavioral tests are needed to form a comprehensive evaluation of infant hearing status.
Although ASSR tests use automated algorithms to obtain results, the interpretation of these test results within a clinical context is not automatic. Audiologists are responsible for the integration and synthesis of test results to determine auditory system status. The discerning and informed professional—who understands the underlying physiologic principles, advantages, and limitations of various evoked response audiometry methods—may use ASSR with confidence. ASSR results can be a significant component of a comprehensive pediatric audiologic evaluation aimed at determining the degree and type of hearing loss.
Acknowledgements: The author is grateful for discussion with Sasha John and Gary Rance. The opinions expressed are the author’s alone.
Disclosures: Barbara Cone is listed on the GSi-Audera patent, and receives royalties from the University of Melbourne based upon the sales of Audera. She received support from Intelligent Hearing Systems, which provided instrumentation enabling her to conduct the research that resulted in Cone & Garinis, “Infant ASSR and Speech Feature Perception” (published in the Journal of the American Academy of Audiology, 2009).
Resources

Roles, Knowledge, and Skills: Audiologists Providing Clinical Services to Infants and Young Children Birth to 5 Years of Age. Available at www.asha.org/policy/KS2006-00259/.

Year 2007 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs (Joint Committee on Infant Hearing). Available at www.asha.org/policy/PS2007-00281/.

Guidelines for Audiologists Providing Informational and Adjustment Counseling to Families of Infants and Young Children With Hearing Loss Birth to 5 Years of Age. Available at www.asha.org/policy/GL2008-00289/.

Guidelines for Competencies in Auditory Evoked Potential Measurement and Clinical Applications(Ad Hoc Committee on Auditory Evoked Potentials, ASHA). Available at www.asha.org/policy/KS2003-00020/.

EHDI Pediatric Audiology Links to Services (PALS): A National Pediatric Audiology Facilities Directory. Available at www.asha.org/aud/Articles/EHDI-Pediatric-Audiology-Links-to-Services-(PALS)--A-National-Pediatric-Audiology-Facilities-Directory.

Patient Education Materials(Audiology Information series, ASHA). Available at www.asha.org/aud/pei.htm.

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Volume 17, Issue 10