Discrimination of the spatial distribution of concurrently active sound sources: some experiments with stereophonic arrays.

Several experiments are described in which subjects were required to discriminate differences in the spatial distribution of concurrently active sound sources in stereophonic arrays. For pure tone stimuli and binaural listening, systematic discrimination functions were observed when relatively small intersource frequency differences (approximately 30 Hz) were present. For tonal stimuli, this discrimination task was reliably performed only for frequencies below 1500 Hz. Additional tests were conducted with amplitude-modulated tonal stimuli, low- and high-frequency uncorrelated noise, correlated low-frequency noise, and, with the uncorrelated low-frequency noise, for stimuli presented in both the vertical plane and under monaural listening conditions. The results of all of these manipulations support the notion that the spatial distribution of sources in a stereophonic array can be appreciated if disparate low-frequency energy is available from the sources in a horizontal configuration. The implications of these results are discussed relative to acoustic processing in the natural environment.