Binaural signal detection, overall masking level, and masker interaural correlation: revisiting the internal noise hypothesis.

This study provides data concerning the characteristics of internal noise that limits binaural detection at 500 Hz under "pulsed" masking conditions and evaluates whether the parameters of such internal noise depend upon masker/signal duration. A single-interval adaptive procedure was employed to measure NoSpi detection thresholds as a joint function of the level of broadband masking noise and masker/signal duration. Spi detection thresholds were also measured as a joint function of the interaural correlation of the masker and masker/signal duration. Findings include : (1) changes in Spi thresholds taken either as a function of diotic masker level or as a function of masker interaural correlation are independent of masker/signal duration; (2) 500-Hz "quiet" So and Spi thresholds yield a masking-level difference of -2.0; (3) reductions in thresholds with increasing duration are similar regardless of masker level. Analyses indicate: (1) the presence of stimulus-independent, interaurally-negatively-correlated, additive internal noise and stimulus-dependent internal noise having a level proportional to that of the external masker while being independent of masker/signal duration; (2) that NoSpi thresholds taken as a joint function of masker/signal duration and masker spectrum level are, quantitatively, well described by taking into account effects produced by the combination of internal and external noises.