Within- and across-listener performance variability in discrimination of interaural time and level differences

Abstract

The ability to discriminate changes in interaural time differences (ITDs) and interaural level differences (ILDs) varies markedly both within and across individuals. Such variability has been frequently noted, but rarely systematically investigated. Here, both forms of variability, expressed in terms of coefficients of variation (mean divided by standard deviation), were examined across a variety of ITD and ILD conditions in a total of 84 naive listeners. Three consistent patterns emerged. First, across-listener variability was relatively constant across ITD and ILD discrimination, suggesting that this variability might be determined by factors common to the processing of both cues. Second, compared to across-listener variability, within-listener variability was larger for the ITD conditions but smaller for the ILD conditions, suggesting that, within individuals, ITD processing may have a higher level of internal noise than ILD processing. Third, stimulus frequency (ranging from 0.3 to 6 kHz) and stimulus type (pure tones and sinusoidally amplitude modulated tones) had little influence on either type of variability, suggesting that variability was determined by cue-dependent, rather than stimulus-dependent mechanisms. The systematic nature of these variability patterns illustrates that examination of variability can provide important insights into the processing of interaural cues. [Work supported by NIH.]