The role of sensitivity to transients in the detection of appearing and disappearing objects in complex acoustic scenes.

We report a series of psychophysics experiments that investigated listeners' sensitivity to changes in complex acoustic scenes. Specifically, we sought to test the hypothesis that change detection is supported by sensitivity to change-related transients (an abrupt change in stimulus power within a certain frequency band, associated with the appearance or disappearance of a scene element). This hypothesis, in the context of natural scenes, is commonly dismissed on account that the elements of the scene may themselves be characterized by on-going energy fluctuations that would mask any genuine change-related transients. We created artificial 'scenes' populated by multiple pure-tone components. Tones were modulated (by a square wave at a distinct rate) so as to mimic the fluctuation properties of complex sounds. "Change" was defined as the appearance or disappearance of one such element. Importantly, such scenes lack semantic attributes, which may have been a limiting factor in interpreting previous auditory change-detection studies, thus allowing us to probe the low-level, pre-semantic, processes involved in auditory change perception. In Experiment 1 we measured listeners' ability to detect item appearance and disappearance in conditions where change-related transients are masked by a silent gap. In Experiment 2, we investigated the effect of an acoustic distractor - a brief signal that occurs at the time of change, but does not mask any scene components. The data show that gaps adversely affected the processing of item appearance but not disappearance. However, distractors reduced both -appearance and disappearance detection. Together our results suggest a role for sensitivity to transients in the process of auditory change detection, similar to what has been demonstrated for visual change detection.