The import of within-listener variability to understanding the precedence effect

The purpose of this study was to gather behavioral data concerning the precedence effect as manifested by the localization-dominance of the leading elements of compound stimuli. This investigation was motivated by recent findings of Shackleton and Palmer [(2006). J. Assoc. Res. Otolaryngol. 7, 425-442], who measured the electro-physiological responses of single units in the inferior colliculus of the guinea pig. The neural data from Shackleton and Palmer indicated that processing of binaural cues like those relevant to understanding localization dominance is greatly affected by internal, neural noise. In order to evaluate the generality of their physiological results to human perception, the present study measured localization dominance so that behavioral responses within and across sets of samples (i.e., tokens) of frozen noises could be compared. Conceptually consistent with Shackleton and Palmer's neural data, the variability of perceived intracranial lateral positions produced by repeated presentations of the same tokens of noise was greater than the variability of intracranial lateral positions measured across different tokens of noise. This was true for each of the four individual listeners and for each of the 72 stimulus conditions studied. Thus, measured either neuro-physiologically (Shackleton and Palmer, 2006) or behaviorally (this study), the import of within-listener variability appears to be a general, intrinsic aspect of binaural information processing.