Intelligibility of spondees via bone conduction at elevated presentation levels

Abstract

Speech reception threshold testing by bone conduction is very useful in diagnostic audiometry. However, there are little data regarding the CID W-1 spondee word lists used with the Radioear B-71 and B-72 and Pracitronic KH 70 bone conduction vibrators at higher presentation levels for testing hearing impaired clients. Data are needed in order that results of speech reception thresholds using the CID W-1 word lists via these three bone conduction vibrators at higher intensity levels can be used confidently in the clinic. More data are available for speech reception thresholds using the CID W-1 word lists via earphones. This study compared speech intelligibility presented via bone conduction at higher intensity levels to that presented via earphone at higher intensity levels. Twelve normal hearing adults, with thresholds artificially elevated by binaural speech noise masking to simulate a hearing impairment, were used as subjects. Recorded CID W-1 spondee word lists were presented via four transducers: Radioear B-71, Radioear B-72, and Pracitronic KR 70 bone vibrators, and a TDH-39 earphone. Investigation of each bone conduction vibrator was accomplished by using forehead placement and using binaural speech noise masking via earphones. Investigation of the earphone was accomplished by simultaneously presenting binaural speech stimuli and speech noise masking. Spondees from the CID W-1 word lists were presented to the subject via a transducer. A bracketing technique was used to estimate the speech reception threshold. Using the intensity level of the predetermined SRT as 0 dB, each list was presented at one of the following levels: +4, +2, O, -2, -4, and -6. Performance-intensity functions, the percentage of correctly identified spondees as a function of presentation level, were obtained for each transducer. The percentage of spondees correctly identified increased with the stimulus level for all transducers. Using linear regression, the line of best fit was calculated for each subject's data under each transducer condition. A one way analysis of variance indicated that there was a significant difference in the slopes of the performance-intensity functions of the transducers. A follow-up test for the one way analysis of variance indicated that there was a signficant difference between the TDH-39 earphone and each of the bone conduction vibrators. There were no significant differences among the bone conduction vibrators. Results of the study suggested that CID W-1 word lists and the 50 percent criterion may be inappropriate for use with these bone conduction vibrators at higher intensity levels. Given that