Influence of spatial and non-spatial feature continuity on cortical alpha oscillations

Abstract

In everyday environments, listeners face the challenge of parsing the sound mixture reaching their ears into individual sources. Perceptual continuity of acoustic features, such as pitch or location, has an obligatory effect on auditory attention even when a feature is not task relevant. Cortical alpha oscillations (8-12 Hz) are thought to functionally inhibit the processing of task-irrelevant information. Here, we hypothesize that discontinuities in a task-irrelevant feature disrupt the attentional modulation of alpha rhythms. Using electroencephalography in humans, we compare physiological measures during a selective auditory attention task where listeners were asked to attend to either talker, based on gender (male or female) or location (left or right). On half of the trials, a discontinuity was introduced in the task-irrelevant acoustic feature. When listeners attended to the talker, there was no evidence of alpha power lateralization, and no effect of a discontinuity in location. In contrast, when listeners attended to location, parieto-occipital alpha power increased ipsilateral to the attended location; moreover, a discontinuity in talker reduced alpha power and disrupted alpha lateralization. Our findings support the importance of parieto-occipital alpha in suppressing sources when listeners focus spatial, but not non-spatial, attention, and show that task-irrelevant discontinuities affect these alpha rhythms.