Occlusion effect: bone conduction speech audiometry using forehead and mastoid placement.

The occlusion effect (OE) was determined for bone conduction speech reception thresholds (SRTs) in 24 normally hearing subjects using forehead and mastoid placement. Results indicated that the OE was about 3 dB greater using forehead as opposed to mastoid placement. The intersubject variability of the OE is similar for the forehead and mastoid positions. The formula for effective masking for bone conduction speech should be equal to the minimum masking level for bone conduction speech plus the air-bone gap of the nontest ear plus 18 dB to account for the OE when using mastoid placement.