Detection thresholds were measured for interaural time differences (ITDs) and interaural level differences (ILDs) that were carried by probe segments embedded in otherwise diotic broadband noise (fringe). The duration of the probe was varied between 5 and 200¿ms, and the duration of the fringe was between 5 and 100¿ms. Consistent with results of Akeroyd and Bernstein [(2001). J. Acoust. Soc. Am. 110, 2516–2526], it was found that a 5-ms fringe placed before a 5-ms probe (forward fringe) led to a larger threshold elevation than a 5-ms fringe placed after the probe (backward fringe). As suggested by Akeroyd and Bernstein, this effect was accounted for by a model providing an onset emphasis of a factor of 2. In contrast, for longer probe and fringe durations, which have not been tested before, a backward fringe had a stronger effect than a forward fringe. This surprising effect was accounted for by an extended model that provided an offset emphasis of a factor of 11 for a 50-ms probe and a 100-ms fringe.