Towards a listening in spatialized noise test using complex tones

The Listening in Spatialized Noise-Sentences (LiSN-S) test has been widely applied to diagnose spatial processing disorder in both normally hearing and hearing impaired listeners who are proficient in English. The overall goal of the present study is to develop a spatial listening test that assesses similar spatial auditory processes as the LiSN-S test but does not rely on speech input and thus, is language independent. Therefore a three-alternative forced choice (3AFC) stream segregation task was implemented using a series of continuously in- or decreasing tone-complexes as targets and random tone-complexes as distractors and foils. Similar to the LiSN-S test the signals were either spatially co-located or separated using non-individualized HRTFs and the difference in thresholds defined the spatial release from masking (SRM). In order to achieve similar large SRM effects (of up to 14 dB) as observed with the LiSN-S test in normal hearing listeners, temporal jitter had to be introduced. The effect of the amount of temporal jitter was investigated on the SRM as a function of tone-complex duration. The results revealed that a jitter of about 30ms in combination with a tone-complex duration of about 30ms is sufficient to elicit the desired SRM.