Localization in the presence of a distracter and reverberation in the frontal horizontal plane. I. Psychoacoustical data

The ability to localize a sound in the free field emitted from one direction (noise burst, 200-ms duration, 20-ms cos(2)-ramps) in the presence of another sound emitted from a different direction (noise burst, 500-ms duration, 20-ms cos(2)-ramps) is measured in anechoic and reverberant virtual environments using individual head-related transfer functions (HRTFs). The target is presented from 13 directions in steps of 15degrees in the frontal-horizontal plane at different power ratios of target and distracter (T/D-ratio), measured before they are filtered with the HRTFs. The distracter is placed at 0degrees, 30degrees or 90degrees azimuth. When the T/D-ratio is set at 0 dB, the perceived directions of the target were significantly shifted away from the actual location of the target in the opposite direction of the distracter location for all distracter directions. This phenomenon is found for all stimuli presented in an anechoic and in a reverberant environment. With decreasing T/D-ratio, the listeners give similar responses for adjacent angles. At the lowest test condition (which was set individually to -12 dB or -15 dB), the listeners' answers can be grouped into the following general target positions: left, front and right. In the reverberant condition, this effect is observed at T/D-ratios of -7 dB or -10 dB. Measurements of masked detection thresholds in a further experiment show that the listeners cannot detect the target when it is presented at the direction of the distracter (0degrees azimuth) at T/D-ratios below -5 dB. A 2A-4IFC discrimination experiment in the anechoic condition reveals that the listeners are unable to discriminate between target angles up to 45degrees apart for low T/D-ratios (less than or equal to -12 dB).