INTENSITY DISCRIMINATION FOR PRECEDENCE EFFECT STIMULI

When two identical stimuli are presented from two loudspeakers with a brief delay between them, a single image is heard near the source of t he leading sound. The delayed sound or echo appears to be suppressed w hereas the preceding sound determines perceived location, hence the na me, the precedence effect. This study investigated normal-hearing list eners' sensitivity to changes in the intensity of the lagging sound. P airs of 2-ms white noise bursts, with a 2-ms delay between the onsets of lead and lag, were presented from two loudspeakers 45 degrees left and right of midline in an anechoic chamber. A 2AFC procedure was used to test discrimination of intensity changes in the lead, lag, and bot h sounds together. The untreated results showed discrimination to be p oorest for changes in the lag stimulus. However, when the intensity di fferences were transformed into predictions of equivalent monaural lev el based on KEMAR measurements and binaural loudness summation, discri mination for the lag was equal to the other two conditions. A follow-u p experiment found that listeners were highly sensitive to the presenc e of the lag, more sensitive than would be predicted from loudness cha nges. It is concluded that the precedence effect does not consist of a general suppression or attenuation of the lagging sound, but rather t hat suppression may be limited to directionality cues. (C) 1998 Acoust ical Society of America.