Previous findings have suggested that auditory attention causes not only enhancement in neural processing gain, but also sharpening in neural frequency tuning in human auditory cortex. The current study was aimed to reexamine these findings. Specifically, we aimed to investigate whether attentional gain enhancement and frequency sharpening emerge at the same or different processing levels and whether they represent independent or cooperative effects. For that, we examined the pattern of attentional modulation effects on early, sensory-driven cortical auditory-evoked potentials occurring at different latencies. Attention was manipulated using a dichotic listening task and was thus not selectively directed to specific frequency values. Possible attention-related changes in frequency tuning selectivity were measured with an adaptation paradigm. Our results show marked disparities in attention effects between the earlier N1 deflection and the subsequent P2 deflection, with the N1 showing a strong gain enhancement effect, but no sharpening, and the P2 showing clear evidence of sharpening, but no independent gain effect. They suggest that gain enhancement and frequency sharpening represent successive stages of a cooperative attentional modulation mechanism that increases the representational bandwidth of attended versus unattended sounds.

Attending to a visual stimulus feature, such as color or motion, enhances the processing of that feature in the visual cortex. Moreover, the processing of the attended object's other, unattended, features is also enhanced. Here, we used functional magnetic resonance imaging to show that attentional modulation in the auditory system may also exhibit such feature- and object-specific effects. Specifically, we found that attending to auditory motion increases activity in nonprimary motion-sensitive areas of the auditory cortical “where” pathway. Moreover, activity in these motion-sensitive areas was also increased when attention was directed to a moving rather than a stationary sound object, even when motion was not the attended feature. An analysis of effective connectivity revealed that the motion-specific attentional modulation was brought about by an increase in connectivity between the primary auditory cortex and nonprimary motion-sensitive areas, which, in turn, may have been mediated by the paracingulate cortex in the frontal lobe. The current results indicate that auditory attention can select both objects and features. The finding of feature-based attentional modulation implies that attending to one feature of a sound object does not necessarily entail an exhaustive processing of the object's unattended features.