Audiometrically-defined “slight” or “hidden” hearing losses can be manifested as changes in binaural detection

Abstract

We hypothesized that audiometrically-defined “slight” or “hidden” hearing losses might be associated with losses in binaural detection via degradations in precision of coding of interaural temporal disparities (ITDs). Thirty-one listeners were tested using masking configurations that, taken together, allow one to describe how precision of ITD-coding varies as a function of reference ITD and center frequency. Binaural detection thresholds at 500 Hz and 4 kHz were found to increase magnitude of ITD, consistent with there being a loss of precision of ITD-coding that increases with magnitude of ITD. Binaural detection thresholds were elevated, across all ITDs, for those listeners whose absolute thresholds at 4 kHz exceeded 7.5 dB HL, but were not greater than 23 dB HL. No such elevations were observed in conditions having no binaural cues available to aid detection (i.e., “monaural” conditions). Partitioning and analyses of the data revealed the elevated thresholds: 1) were more attributable to hearing level than to age; 2) result from increased levels of internal binaural-processing noise. Our conclusion is that listeners whose high-frequency monaural hearing status would be classified audiometrically as being normal or “slight loss” could still suffer from perceptually meaningful losses of binaural processing.