Neural Mechanisms of Selective Auditory Attention

Abstract

A fundamental goal of selective attention studies is to specify at which levels of sensory processing different kinds of information are selected or rejected. One key issue is whether stimulus selection occurs at early thalamic and primary cortical areas, or at levels of “higher” secondary and association cortex. In the auditory modality, selective attention to an attended stimulus elicits a large negative deflection, the “Nd” or “processing negativity” component. The physiological substrates of this selective attention effect remains controversial. Some authors have argued that the Nd wave represents (at least in part) an enhancement of the auditory evoked N1 wave, possibly by a mechanism of sensory gating (eg., Hillyard,1981), while others have suggested that the Nd arises from a wholly separate generator system (eg., Naatanen, 1982). Previous results from our laboratory suggest that the late Nd (Ndl) elicited under conditions of a long and constant inter-stimulus interval (ISI), stems from a region of auditory cortex distinct from that generating the evoked N1 component: possibly from auditory association areas (Arthur et al., 1989). Under conditions of a fast, variable ISI, selective attention elicits an additional component, the early Nd (Nde). We are using magnetoencephalography to assess the physiological substrates of both the early and late selective attention processes which occur at a fast, variable ISI.