Evidence for spatial tuning in informational masking using the probe-signal method.

Auditory spatial attention is one mechanism that may contribute to the ability to identify one sound source in a multi-source environment. The role of auditory spatial attention in a multi-source environment was investigated using the probe-signal method. The experiment took place in a quiet room with seven speakers arranged in a semi-circle in front of the listener. The speakers were placed at 30-degree intervals at a distance of 5 ft from the listener. The signal was comprised of eight contiguous, 60-ms pure-tone bursts arranged in either a rising or falling frequency pattern. Masker components were also comprised of eight contiguous pure-tone bursts but with durations that varied randomly from 20 to 100 ms. The six maskers were played with the signal and were constructed in order to result in informational rather than energetic masking. The frequency of each masker component was chosen randomly on each burst from a narrow frequency band, independent from the signal frequency band. The task was 1I-2AFC fixed-level identification with response time measurement. The listener was instructed to focus attention on a specified speaker (expected location) for a block of trials. Accuracy and response time were compared across two conditions: (1) signal presented at the expected location and (2) signal presented at an unexpected location. Results indicate a significant increase in accuracy and faster response time when the signal was presented at the expected location as compared to an unexpected location. These results suggest that auditory spatial attention plays an important role in multi-source listening, especially when the listening environment is complex and uncertain.