Relations among Auditory Brainstem and Middle Latency Response Measures, Categorical Loudness Judgments, and Their Associated Physical Intensities

Repeated Measurement of Absolute and Relative Judgments of Loudness: Clinical Relevance for Prescriptive Fitting of Aided Target Gains for soft, Comfortable, and Loud, But Ok Sound Levels

This study was undertaken with the purpose of streamlining clinical measures of loudness growth to facilitate and enhance prescriptive fitting of nonlinear hearing aids. Repeated measures of loudness at 500 and 3,000 Hz were obtained bilaterally at monthly intervals over a 6-month period from three groups of young adult listeners. All volunteers had normal audiometric hearing sensitivity and middle ear function, and all denied problems related to sound tolerance. Group 1 performed judgments of soft and loud, but OK for presentation of ascending sound levels. We defined these judgments operationally as absolute judgments of loudness. Group 2 initially performed loudness judgments across a continuum of seven loudness categories ranging from judgments of very soft to uncomfortably loud for presentation of ascending sound levels per the Contour Test of Loudness; we defined these judgments as relative judgments of loudness. In the same session, they then performed the absolute judgments for soft and loud, but OK sound levels. Group 3 performed the same set of loudness judgments as did group 2, but the task order was reversed such that they performed the absolute judgments initially within each test session followed by the relative judgments. The key findings from this study were as follows: (1) Within group, the absolute and relative tasks yielded clinically similar judgments for soft and for loud, but OK sound levels. These judgments were largely independent of task order, ear, frequency, or trial order within a given session. (2) Loudness judgments increased, on average, by ∼3 dB between the first and last test session, which is consistent with the commonly reported acclimatization effect reported for incremental changes in loudness discomfort levels as a consequence of chronic bilateral hearing aid use. (3) Measured and predicted comfortable judgments of loudness were in good agreement for the individual listener and for groups of listeners. These comfortable judgments bisect the measured levels judged for soft and for loud, but OK sounds. (4) Loudness judgments within the same loudness category varied across listeners within group by as much as 50 to 60 dB. Such large variation in judgments of loudness is problematic, especially because hearing-impaired listeners are known to exhibit similarly large ranges of intersubject response variation and, yet, poplar prescriptive fitting strategies continue to use average rather than individual loudness data to fit nonlinear hearing aids. The primary conclusions drawn from these findings are that reliable absolute judgments of soft and loud, but OK are clinically practical and economical to measure and, from these judgments, good estimates of comfortable loudness can also be predicted for individuals or for groups of listeners. Such loudness data, as measured as described in this report, offer promise for streamlining and enhancing prescriptive fitting of nonlinear hearing aids to target gain settings for soft (audible), comfortable, and loud, but OK (tolerable) sound inputs for the individual listener.

Auditory Brainstem and Middle Latency Responses Measured Pre- and Posttreatment for Hyperacusic Hearing-Impaired Persons Successfully Treated to Improve Sound Tolerance and to Expand the Dynamic Range for Loudness: Case Evidence

In this report of three cases, we consider electrophysiologic measures from three hyperacusic hearing-impaired individuals who, prior to treatment to expand their dynamic ranges for loudness, were problematic hearing aid candidates because of their diminished sound tolerance and reduced dynamic ranges. Two of these individuals were treated with structured counseling combined with low-level broadband sound therapy from bilateral sound generators and the third case received structured counseling in combination with a short-acting placebo sound therapy. Each individual was highly responsive to his or her assigned treatment as revealed by expansion of the dynamic range by at least 20 dB at one or more frequencies posttreatment. Of specific interest in this report are their latency and amplitude measures taken from tone burst-evoked auditory brainstem response (ABR) and cortically derived middle latency response (MLR) recordings, measured as a function of increasing loudness at 500 and 2,000 Hz pre- and posttreatment. The resulting ABR and MLR latency and amplitude measures for each case are considered here in terms of pre- and posttreatment predictions. The respective pre- and posttreatment predictions anticipated larger pretreatment response amplitudes and shorter pretreatment response latencies relative to typical normal control values and smaller normative-like posttreatment response amplitudes and longer posttreatment response latencies relative to the corresponding pretreatment values for each individual. From these results and predictions, we conjecture about the neural origins of the hyperacusis conditions (i.e., brainstem versus cortical) and the neuronal sites responsive to treatment. The only consistent finding in support of the pre- and posttreatment predictions and, thus, the strongest index of hyperacusis and positive treatment-related effects was measured for MLR latency responses for wave Pa at 2,000 Hz. Other response indices, including ABR wave V latency and wave V-V' amplitude and MLR wave Na-Pa amplitude for 500 and 2,000 Hz, appear either ambiguous across and/or within these individuals. Notwithstanding significant challenges for interpreting these findings, including associated confounding effects of their sensorineural hearing losses and differences in the presentation levels of the toneburst stimuli used to collect these measures for each individual, our limited analyses of three cases suggest measures of MLR wave Pa latency at 2,000 Hz (reflecting cortical contributions) may be a promising objective indicator of hyperacusis and dynamic range expansion treatment effects.