Binaural interference in the free field.

In an anechoic chamber the minimum audible angle (MAA) was measured in seven normal-hearing adults for a narrow band of noise centered at 4000 Hz (target). In the absence of an interfering stimulus, the average MAA was 2.1°. When a low-frequency interferer (a narrow band of noise centered at 500 Hz) was pulsed on and off with the target from directly in front of the subject, the average MAA was significantly elevated (13.4°). However, if the interferer was continuously present, or if it consisted of two independent noises presented from ±90°, interference was much reduced. The interference effect was asymmetric: a high-frequency interferer did not result in elevation of MAA threshold for a low-frequency target. These results are similar to those that have been extensively reported for stimuli under headphones [Bernstein and Trahiotis (1995). J. Acoust. Soc. Am. 98, 155-163]. These data are consistent with the notion that interference from a spectrally remote low-frequency interferer occurs in the free field to the extent that the target and interferer are fused into a single perceptual object. If cues are provided that promote perceptual segregation (such as temporal onset differences or spatial location differences), the interference is reduced or eliminated.