Directional Perception of Multiple Sound Sources Based on Envelope Cues Bernhard Seeber and Ervin Hafter University of California, Berkeley Cochlear implants (CIs) transmit channel-wise envelope information to the auditory nerve. Using that strategy CIs were successful to restore the ability to understand speech in quiet, but patients encounter great difficulties in a noisy background. The precedence effect describes the suppression of the directional influence of a lagging sound on the localization of a leading sound. Since precedence relies on the evaluation of ITDs at low frequencies, it is interesting to see if altered cues with CIs carry enough information for the precedence effect. Experiments are done in the simulated open-field environment, a calibrated loudspeaker setup in our anechoic chamber. Subjects judge the apparent location of sounds played with varying delay from speakers at ±30°, using a movable visual pointer. Two out of four bilateral CI-subjects showed some localization ability, but no evidence for the precedence effect arose. Concurrent sounds were localized in the middle between the two loudspeakers as known from summing localization. In opposite to normal hearing, patients localized two sound directions even for small delay times - one corresponding to each loudspeaker position. No suppression of the echo takes place. Studies with vocoder-simulations of CIs are underway to clarify if the information present in ILDs and envelope-ITDs is sufficient to evoke the precedence effect in normal hearing subjects. Support provided by NIH and NOHR. The talk will be held in German.