Abstract:

To better understand the parameters that limit interaural-delay sensitivity in a precedence-effect task, psychometric functions were measured for the detection of an interaural time difference (ITD) in the second transient of a two-transient binaural stimulus. The stimuli were broadband 1-ms Gaussian pulses centered on the cosine phase of a 6-kHz carrier. Twenty-point psychometric functions were obtained using a 2IFC method of constant stimuli, with each point based on a minimum of 500 trials. Four functions were obtained for each observer at interclick intervals (ICI) of 3, 6, and 12 ms, in addition to a single-transient control condition. Proportion of correct responses were transformed to d[sup '] units and linearly fitted with ln(d[sup '])=ln (beta)+(upsilon) ln((Delta)ITD), where ln (beta) and (upsilon) are the parameters of the fit. The slope parameter (upsilon) was independent of ICI and remained near unity, discounting nonlinear transformations of the stimulus scale [J. P. Egan, J. Acoust. Soc. Am. 38, 1043--1049 (1965)]. However, ln (beta) decreased with decreasing ICI, suggesting linear changes in either the variance or expected value of the perceived lateral position. Further experiments examined the contribution of each of these latter factors to changes in ln (beta). Implications for causes that underlie the precedence effect are discussed.