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

This study characterizes changes in response properties of toneburst-evoked auditory brainstem responses (ABRs) and/or middle latency responses (MLRs) as a function of perceived loudness and physical intensity of these stimuli and delineates the range of levels corresponding to categorical loudness judgments for these stimuli. ABRs/MLRs were recorded simultaneously to 500- and 2,000-Hz tonebursts in 10 normal-hearing adults at levels corresponding to each listener's loudness judgments for four categories on Contour Test of Loudness. Group mean ABR wave V and MLR wave Pa latency values increased significantly as loudness judgments decreased. Group mean amplitude values for ABR wave V-V' and MLR wave Na-Pa increased as the listeners' categorical judgments increased. Listeners assigned a broad range (30 to 40 dB) of stimulus intensities when judging loudness of these stimuli within a specific loudness category. This was true for all four loudness categories and both frequencies. Thus, it appears that tone-evoked ABR/MLR response measures reflect, in part, the listener's perception of loudness. Response latencies are a more sensitive indicator of listener's loudness percept than corresponding response amplitudes. An appreciable range of signal levels was judged to be categorically equivalent across listeners. Thus, limiting how loudness judgments can be applied to prescriptive hearing aid fittings in individuals who cannot provide accurate loudness judgments.