Processing of the unattended message during selective dichotic listening

The role of attention in auditory information processing as revealed by event-related potentials and other brain measures of cognitive function

This article examines the role of attention and automaticity in auditory processing as revealed by event-related potential (ERP) research. An ERP component called the mismatch negativity, generated by the brain's automatic response to changes in repetitive auditory input, reveals that physical features of auditory stimuli are fully processed whether or not they are attended. It also suggests that there exist precise neuronal representations of the physical features of recent auditory stimuli, perhaps the traces underlying acoustic sensory (“echoic”) memory. A mechanism of passive attention switching in response to changes in repetitive input is also implicated.

Conscious perception of discrete acoustic stimuli might be mediated by some of the mechanisms underlying another ERP component (NI), one sensitive to stimulus onset and offset. Frequent passive attentional shifts might accountforthe effect cognitive psychologists describe as “the breakthrough of the unattended” (Broadbent 1982), that is, that even unattended stimuli may be semantically processed, without assuming automatic semantic processing or late selection in selective attention.

The processing negativity supports the early-selection theory and may arise from a mechanism for selectively attending to stimuli defined by certain features. This stimulus selection occurs in the form ofa matching process in which each input is compared with the “attentional trace,” a voluntarily maintained representation of the task-relevant features of the stimulus to be attended. The attentional mechanism described might underlie the stimulus-set mode of attention proposed by Broadbent. Finally, a model of automatic and attentional processing in audition is proposed that is based mainly on the aforementioned ERP components and some other physiological measures.

Implications of ERP data for psychological theories of attention

The contribution of the event-related potential (ERP) research to understanding human selective attention will be evaluated. A closely related issue, the starting point of the present treatment, involves the nature and extent of automaticity in information processing. The mismatch-negativity component of the ERP suggests that the basic, obligatory, processing of the physical features of auditory stimuli is unaffected by the direction of attention. These data also reveal a possible mechanism for attention switching to stimulus change occurring in the unattended input, observed by cognitive psychologists. The N1 wave of the ERP might in turn provide a data base for explaining similar attention switches to stimulus onsets after breaks in stimulation and to offsets of long-duration stimuli. With regard to selective attention, the processing negativity might make it possible to delineate the central principle of stimulus selection in attention, a goal probably inaccessible to non-physiological attention research. In the visual modality, cognitive psychologists have found that spatial attention is more fundamental and powerful in stimulus selection than any other form of visual selective attention. Consistently, ERP data show that the exogenous components in vision are enhanced by spatial selective attention but not when attended and unattended stimuli are not spatially separated. Also, ERP data (the P3 wave) give support to certain forms of resource-allocation theories of attention. In addition, with regard to the currently popular distinction between automatic versus controlled processing, these data strongly suggest that extended consistent-mapping training does not lead to a "genuine" automatization of a search process in the sense of independence of a limited-capacity system.