Evidence Integration in Natural Acoustic Textures during Active and Passive Listening

Abstract

Many natural sounds can be well described on a statistical level, for example wind, rain or applause. Even though the spectro-temporal profile of these acoustic textures is highly dynamic, changes in their statistics are indicative of relevant changes in the environment. Here, we investigated the neural representation of change detection in natural textures in humans, and specifically addressed whether active task engagement is required for the neural representation of this change in statistics.

Subjects listened to natural textures whose spectro-temporal statistics were modified at variable times by a variable amount. Subjects were instructed to either report the detection of changes (active) or to passively listen to the stimuli. A subset of passive subjects had performed the active task before (passive-aware vs. passive-naive). Psychophysically, longer exposure to pre-change statistics was correlated with faster reaction times and better discrimination performance. EEG recordings revealed that the build-up rate and size of parieto-occipital potentials reflected change size and change time. Reduced effects were observed in the passive conditions. While P2 responses were comparable across conditions, slope and height of parieto-occipital potentials scaled with task involvement. Neural source localization identified a parietal source as the main contributor of change-specific potentials, in addition to more limited contributions from auditory and frontal sources.

In summary, the detection of statistical changes in natural acoustic textures is predominantly reflected in parietal locations both on the skull and source level. The scaling in magnitude across different levels of task involvement suggests a context-dependent degree of evidence integration.

Significance Statement The everyday auditory environment is often complex and highly variable. Separating relevant changes from irrelevant variability is important for auditory processing. Previous research has already shown that sensory evidence is integrated to achieve accurate decisions. In the present study, we extend this research in two ways, first by using more realistic and complex stimuli, and second, by modulating the level of engagement of subjects in the task. We demonstrate that dynamic processing of natural stimuli leads to similar neural responses as for synthetic complex stimuli. Further, neural responses continue to reflect properties of the acoustic stimulus even for reduced task engagement, albeit with much lower amplitudes. We conclude that auditory evidence integration may continue even during passive perception.