Indispensable benefits and unavoidable costs of unattended sound for cognitive functioning.

Critical to survival, and also to the organism's efficient management of the flow of information in the brain, is attentional selectivity; the ability to select one source of information to guide action whilst ignoring others that are irrelevant to the current behavioural goal. But such selectivity is not merely the inclusion of the relevant information and the complete neglect of irrelevant information. We discuss in this paper the way that all sound is processed in an obligatory fashion--whether relevant or irrelevant--and discuss the fate of sound in the case when it is irrelevant to the immediate mental task. Using the so-called irrelevant sound paradigm we show that unattended information is both registered and organised. This obligatory process of organisation compromises the efficiency of particular types of mental activity. We discuss how such interference comes about but the key emphasis is upon the possible beneficial effects of such processing-of-the-irrelevant, in allowing the switching of attention to be more facile and intelligent and in allowing the accumulation of evidence about statistical regularities in the auditory world (such as those helpful to the efficient perception, acquisition and use of language). In sum, we describe how purposeful processing based on directed attention is in a state of tension with the obligatory, automatic processing of the unattended. One of the consequences of this tension is typically manifested in auditory distraction, but the benefits of processing of the attended may considerably outweigh this disadvantage.