When a sound is presented in a reverberant environment, listeners usually can localize the sound at the correct source position, being unaware and little influenced by the surrounding reflections. This phenomenon is referred to as the "precedence effect".
Because humans spend much time indoors in a typical reverberant environment, the need for a human to localize sound may cause the human auditory system to adapt to the reverberant environment. It is our opinion that there should be a mechnism which can estimate the level of reflected sounds and emit an inhibition signal to the sound localization mechanism, so that the neural pathway from low to high level of localization processing can be controlled to avoid the influence of reflections. Such a mechanism is possible located in the cochlear nucleus. From this point of view, the precedence effect can be interpreted as an "echo-avoidance" effct.
It consists of two paths, one for localization cue processing and one for inhibition signal generation. We assume that the echo estimation and inhibition mechanism is independent for each frequency. The path of inhibition generation will take a monaural signal, possibly the mixed signal of left and right channels. In the integration process, the first stage will be time averaging for each localization cue in each frequency subband. Integration over different frequency subbands and different cues will then take place. In a broad sense, the integration process also includes both integration and segregation of localization cues for sounds from different sources. The new concept in the EA model is that the precedence effect is a "continuous" effect depending on the relative strength of direct sound and echo, but not an "instantaneous" effect which occurs only at a rapid onset.
- assumption 1:
The precedence effect is an echo-avoidance effect based on the integrated forward inhibition of preceding sounds on localization. - assumption 2:
There is an echo-estimation mechanism which can approximately estimate the total echoes caused by the preceding sounds. - assumption 3:
The amount of forward inhibition of localization depends on the relative strength of observed sounds and estimated echoes.
- Huang, J. and Ohnishi, N. and Guo, X. and Sugie, N.,
"Echo Avoidance in a Computaional Model of the Precedence Effect",
Speech Communication (Elsevier Science),
Vol.27, No.3-4, pp.223-233, 1999.