Abstract for ICA 2007 Madrid, invited talk to binaural session The duplex-theory of localization investigated under natural conditions Bernhard Seeber The duplex theory postulates that low-frequency tones are localized on the basis of interaural time differences (ITDs) while tones above 1.5kHz are localized by evaluating interaural level differences (ILDs). Recent research showed that ITDs are also dominant for wide-band sounds. The contribution of envelope-ITDs is supposedly small. Using tones previous studies investigated the sensitivity to isolated binaural cues or the dependence of image location on traded cues. The current study investigated lateralization for conflicting, but natural ILDs and ITDs by modifying head-related transfer functions. Preliminary results of 3 subjects showed clear ITD-dominance for almost all tested natural and synthetic sounds. Surprisingly, ITDs dominated for flute sounds while for a 2kHz high-pass noise both cues received nearly equal weights. The highest relative ILD-weighting was seen for natural combinations of ILDs and ITDs, while ILDs were usually ignored if cues conflicted. The dominant image was based on ILDs only for high-frequency sounds with strongly opposing cues. Split images were reported for a short melody played on a flute while few splits were heard for a single flute tone. Binaural cue weighting showed large variability between subjects, with one subject being ILD-, and the other two ITD-dominated. PACS: 43.66.Pn - Binaural hearing