The precedence effect: Is it the same for interaural time and interaural level differences?

Until recently, it was believed that the precedence effect operated for both interaural time and interaural level differences (ITDs and ILDs). Stecker and Brown (2010) demonstrated the absence of precedence effects for ILDs under conditions producing strong effects for ITDs. In order to provide a quantitative measure of the precedence effect, echo weights were measured using a correlational analysis as a function of echo delay for both ITDs and ILDs in 14 individuals for judgments based on binaural cues presented by the echo pulse. Stimuli were pairs of 3000-Hz 4-ms Gaussian pulses presented with echo delays between 4 and 96 ms. Echo weights at short echo delays (4 ms) were significantly higher for ILDs (M = 0.445) than ITDs (M = 0.196). Additional data were collected for conditions in which an ITD followed an ILD versus an ILD followed an ITD. Performance was far superior at short echo delays for ILDs following ITDs, with the leading ITD barely exerting any influence on subsequent processing of ILDs. We speculate that the mechanism by which ILDs are extracted (integration of sound pressure over time) makes later non-zero ILDs informative whereas later arriving ITDs provide little information about the location of sound sources.