Spatial audiometry: detection of spondaic words in noise

It is important to select appropriate stimuli and test conditions for developing standardized spatial audiometric tests. In three experiments, binaural detection thresholds (BDTs) for a target signal, located at either 0, 45, 90, 135, 180, 225, 270, or 315 degrees azimuth, were measured in the presence of a masker positioned at one of these eight locations. Target signals included spondaic words from the CID W-1 list. The masker was speech spectrum noise (SSN) or multitalker noise (MTN) presented at a constant level (65 dBA). Bekesy tracking was used to measure BDTs in listeners with normal hearing. Results indicate that BDTs are significantly influenced by the (a) angular separation between the target and noise source and (b) choice of spondaic words used as target stimuli. BDTs for various spondaic words differed as much as 13 dB for a given angular separation. BDTs measured in SSN and MTN for otherwise identical test conditions differed less than 3 dB. A single spondaic word appears to be appropriate for spatial audiometric tests of detection. Nonsignificant differences between masked BDTs obtained for SSN and MTN noises indicate that for spatial detection, the masking effects of these noises are comparable. These results indicate that the development of a clinical test of spatial detection should include the use of SSN and a single spondaic word, with detection being measured for a set of four or five signal and noise source configurations.