Sound source localization: Bandwidth and envelope

Human listeners were asked to locate six sound sources separated by 15o in the right quarter field. Sound sources were located in a sound-deadened room (reverberation time < 90 ms) at the height of the listener's pinna 1.67 meters from the listener. In Experiment 1, eight, 200-ms pure tones covering the frequency range from 250 to 7011 Hz were presented. In Experiment 2, 200-ms noise bursts with different bandwidths (1/6, 1/3/, 1, and 2 octaves) at three center frequencies (250, 2000, and 4000 Hz) were presented. In Experiment 3, 200-ms, 4000-Hz tones were presented with transposed envelopes with rates of 50, 100, 150, and 250 Hz. Several indicators of sound source localization performance were measured including root-mean-square (rms) error in degrees. RMS error decreased with increasing bandwidth from approximately 20 degrees for pure tones to approximately 6 degrees for 2-octave wide noises. RMS error depended on center frequency much more for narrow bandwidths than for broader bandwidths. RMS error decreased slightly from 50-Hz rate of modulation to 250-Hz rate of modulation. The data suggest that stimulus bandwidth is the primary variable effecting sound source localization performance in the free-field.