Factors that increase processing demands when listening to speech

Abstract

Listening effort is an increasingly important concept for applied hearing researchers, but it has not been well elaborated in the cognitive literature. We propose that listening effort is the product of two factors: the processing demands imposed by the listening situation, and the cognitive resources that an individual brings to bear, to compensate for demands. Whereas cognitive resources differ markedly among individuals, processing demands are generally constant in a given listening situation, at least for normal-hearing individuals, and fall into at least three different categories: (i) perceptual demands, (ii) linguistic demands, and (iii) concurrent task demands. Perceptual demands are increased when the speech is degraded, when concurrent interfering sounds are present, or when the listener is hearing impaired. Linguistic demands are increased, for example, when speech is semantically or syntactically complex, or when meaning is ambiguous. Finally, when a listener is performing another task (such as driving) while hearing speech, additional demands are present. A series of behavioral and neuroimaging experiments reveals the nature of these different demands, which appear to be largely independent but to interact in left inferior frontal cortex; fMRI activity in this area may serve as an objective, quantifiable, measure of listening effort. Interactions among different types of demand imply that they cannot be fully understood by studying them in isolation.