Interaural Grouping and the Precedence Effect

The precedence effect has been viewed in the literature mostly as an independent mechanism of the auditory system with the aim to alleviate interfering effects of reflections. The precedence effect process is mostly thought to be bottom-up, as are the models of it, but some literature also suggests high level influence [1, 3]. Our previous results on precedence with cochlear implant simulations show that the effect has to be seen in the larger context of auditory scene analysis (ASA) [4]. ASA studies the mechanisms that lead to fusion and segregation of sound components into auditory objects. Prominent features for ASA are the common onset of components, common fundamental frequency, and synchronized amplitude and frequency modulation [2]. In a unified theory of auditory perception those Gestalt cues should also govern the precedence effect. At short delays between a leading and a lagging copy of a sound the lag is perceptually integrated, fused with the lead. At delays above the echo threshold (ET) the lag is segregated from the lead. The present study investigates if fusion between lead and lag, as evidenced in the ET, can be influenced by amplitude modulation of lead and lag. The results demonstrate a strong effect of AM, suggesting that fusion and segregation between lead and lag are governed by Gestalt rules. The results further emphasize the importance of envelope cues for the precedence effect while most current models predominantly consider fine structure information.