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Loudness match (LM) measures the perceived loudness level of the tinnitus and is typically reported in sensa- tion level (SL), that is, the level relative to the individual’s auditory threshold. LM is measured by presenting a tone or noise and asking the patient to indicate if the tone is softer or louder than their tinnitus. The intensity of the tone is then adjusted until the patient reports the tone is a comparable loudness to their tinnitus.
To determine the ability of external sounds as a means of tinnitus suppression (i.e., masking), the minimum masking level (MML) is often assessed. The MML is the minimum level of external acoustic stimulation, typically a noise, needed to cover up the patient’s tinnitus perception. In this assessment, a low-level broadband noise (BBN) is presented to the patient via an audiometer. The intensity of the noise is slowly raised until the patient reports they can no longer hear their tinnitus. This measure can be useful in prescrib- ing sound therapy-based recommendations to patients.
Last, many patients report that tinnitus suppression may persist after the masker has been turned off, a phenomenon known as residual inhibition (RI). RI is a measure of the duration of patient-reported tinnitus suppression after a patient has been presented with masking noise. Noise is presented at 10 dB above MML for 60 s. After the procedure, the patient is asked if they experience any difference in their tinnitus. If their tinnitus is suppressed, the duration of sup- pression is timed; this often only lasts for seconds to minutes. Use of this procedure is cautioned, however, because it can exacerbate tinnitus in some patients.
The use of these subjective tinnitus measurements is not ubiquitous among audiologists The reliability of such measurements is often questioned, as is their purpose, and none of these measurements are recommended in the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) (Tunkel et al., 2014) nor the US Department of Veterans Affairs (Henry and Manning, 2019) clinical guidelines. At best, the tinnitus assessment serves to provide a quantification of a person’s tinni- tus perception, which, in turn, may provide a tool in counseling and considerations of sound-based therapy. Nonetheless, the tinnitus assessment does not necessarily differentiate persons with tinnitus and those feigning a tinnitus perception. Furthermore, the results of the tin- nitus assessment described have limited correlation with tinnitus reaction (Manning et al., 2019).
Tinnitus or No Tinnitus?
In 2006, Jim Henry and colleagues at the National Center for Rehabilitative Auditory Research (NCRAR) in Portland, OR, described an automated system for the psychoacoustic assessment of tinnitus. The system was a self-assessment tool using on-screen instructions that allowed the individual with tinnitus to alter frequency and intensity parameters to match the psychoacoustic attributes of their tinnitus percept.
In an interesting twist, the study design included a group of participants with comparable hearing status but that did not report tinnitus, rather they were instructed to feign a tinnitus percept. Henry et al. (2006) reported significant differences in outcomes between the tinnitus and the no-tinnitus group. First, the loudness matches for the tinnitus group were two to four times greater than the no-tinnitus group. Second, the PM was nearly an octave higher for the tinnitus group relative to the no-tinnitus group. Reliability between sessions was not different for the LM, but the no-tinnitus group showed greater variance for PM. The authors proposed develop- ing a statistical method to determine the probability an individual has tinnitus based on variance of the measures.
Perception Versus Reaction
An additional limitation of the psychophysical assessment of tinnitus is the lack of correlation to tinnitus reaction or functional impact (Manning et al., 2019). Numerous scales exist to measure tinnitus reaction (Meikle et al., 2012). Although the relationship between measures of tinnitus perception and reaction is weak, this does not eliminate their relative potential for determining the presence of tinnitus and identifying the affective and functional impact, respectively. Finally, visual numeric rating scales (NRS) and visual analog scales (VAS) to assess tinnitus loudness are additional methods to quan- tify tinnitus perception. However, studies suggest that rather than correlating to loudness, these measures are more reflective of the tinnitus reaction (Hall et al., 2017).
Measuring Tinnitus in Animals
Animal models of tinnitus are important for more inva- sive measures to determine physiological changes related to tinnitus perception and development of potential therapeutics. Early animal studies (Jastreboff et al., 1988) used high doses of sodium salicylate, the active ingre- dient in aspirin, to induce transient tinnitus. Aspirin at
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