The Variability of Occluded and Unoccluded Bone-Conduction Thresholds

Abstract

A series of three experiments of similar basic design was performed on individuals with normal hearing to compare the variability associated with occluded and unoccluded bone-conduction thresholds. Estimates of threshold were obtained at each test frequency for air conduction, unoccluded bone conduction, and occluded bone conduction stimuli. Eleven young adults participated in Experiment I. Their ears were occluded by TDH-39 earphones encased in MX41/AR cushions. In Experiment II 11 young adults were tested with a Grason-Stadler 001 circumaural cushion replacing the MX41/AR cushion. Two types of occluders were compared in Experiment III, using nine subjects with previous experience in Bekesy tracing. The variability of the occluded bone-conduction thresholds was either similar or less than that observed during the unoccluded measurements. The variability of the occlusion effect itself was comparable or less than the variability of the unoccluded or occluded bone-conduction thresholds. The source of the variability stemmed largely from differences between individuals rather than from test-retest variability. Although the variability of the occluded thresholds was reduced slightly when the circumaural cushion was used as compared to the supra-aural cushion, the results of the final experiment did not completely support the earlier finding.