The effect of spectral density and bandwidth on the precedence effect
Bernhard U Seeber


The precedence effect shows the ability of the auditory system to perceptually 
suppress reflections such that a single sound is heard at the direction of the 
leading sound. A low frequency tone is localized on the basis of its interaural 
phase, but the addition of its delayed copy alters the interaural phase and thus 
its location. A larger bandwidth is needed to stabilize localization at the lead 
either through integrating binaural information across frequency or through 
extracting information from the temporal envelope. Increased spectral density will 
give rise to faster envelope fluctuations within an auditory filter, thus 
facilitating the evaluation of binaural cues from the envelope. 

The present study investigated the spectral density needed for the precedence 
effect for ongoing stimuli of various bandwidths. Stable precedence could not be 
obtained at or below 1 Bark bandwidth regardless of the number of tones per 
critical band (CB). Precedence emerges with at least two tones per CB over 2 Bark. 
No precedence was found with one tone per CB which suggests that envelope 
information within a CB is needed. The echo threshold increases with increasing 
bandwidth or spectral density, suggesting that within and across-channel 
information is combined.