The precedence effect for noise bursts of different bandwidths. I. Psychoacoustical data

Abstract

The human ability to localize a direct sound source in the presence of reflected sounds is well known as localization dominance due to the precedence effect, formerly also called ‘‘the law of the first wavefront.’’ The fact that the localization dominance partly fails for signals with a very narrow bandwidth raises the question of whether the localization dominance requires cross-frequency-band interaction. To investigate this, a psychoacoustic experiment was conducted in which the perceived lateralization of a noise burst ( 300s ITD) in the presence of a reflection ( 300s ITD)wasmeasured. The parameters in this experiment were the inter-stimulus interval (ISI) and the bandwidth. The first was varied among the following values: 0.0ms and then from 1.0ms in steps of 0.5ms to 4.0ms. The bandwidth was adjusted to be either 100Hz, 400Hz, or 800Hz. The data of the listeners clearly show that localization dominance becomes more stable, especially with regard to the dependence on the ISI, when the bandwidth is increased. At the smallest bandwidth under examination (100Hz), localization dominance cannot be observed for some of the listeners anymore, while others perceive at least the sound coming from the lateral side where the direct sound source is positioned; nevertheless, their auditory event varies strongly with the ISI. A signal analysis reveals that in the first case, the precedence effect does not seem to have any influence. Here, the listeners rather base their judgements on the ongoing part of the sound. The signal analysis also indicates that it is not necessary to assume that the signals in the different frequency bands interact directly with each other while being processed (e.g., cross-frequency coincidence units). It rather seems to be sufficient to average across those bands.