Cortical mechanisms of auditory spatial attention in a target detection task.

The benefits of spatial attention on stimulus processing are thought to diminish with increased distance from the attended location, indicating an attention gradient. Evidence for attention gradients is provided by spatial attention effects on event-related potentials (ERPs) under conditions of rapid stimulus presentation from closely spaced locations. This study was motivated by ecological considerations which suggest that auditory attention is particularly useful for panoramic orienting to intermittent sounds. Auditory ERPs were recorded from a wide range of horizontal locations (180°) while subjects pressed a button to occasional targets at one attended location. Results showed that an ERP component associated with automatic orienting, the P3a, had linear amplitude increases to non-targets as a function of distance from the attended location. A component prior to the P3a with a latency of ~200ms, the P200, showed a similar pattern but only when subjects attended to the left hemifield. When attending to lateral targets frontal slow waves contralateral to the attended location followed the P3a and were attenuated at greater distances from the target location for at least 1s. Results suggest that auditory spatial attention under low cognitive loads modulates orienting responses as a function of distance from the attended location. The slow wave findings show that information about the relation between a stimulus and the attended location persists well beyond the time of initial sensory processing and may involve frontal regions important for maintaining online representations of task set.