Abstract
Auditory selective attention plays an essential role for identifying sounds of interest in a scene, but the neural underpinnings are still incompletely understood. Recent findings demonstrate that neural activity that is time-locked to a particular amplitude-modulation (AM) is enhanced in the auditory cortex when the modulated stream of sounds is selectively attended to under sensory competition with other streams. However, the target sounds used in the previous studies differed not only in their AM, but also in other sound features, such as carrier frequency or location. Thus, it remains uncertain whether the observed enhancements reflect AM-selective attention. The present study aims at dissociating the effect of AM frequency on response enhancement in auditory cortex by using an ongoing auditory stimulus that contains two competing targets differing exclusively in their AM frequency. Electroencephalography results showed a sustained response enhancement for auditory attention compared to visual attention, but not for AM-selective attention (attended AM frequency vs. ignored AM frequency). In contrast, the response to the ignored AM frequency was enhanced, although a brief trend toward response enhancement occurred during the initial 15 s. Together with the previous findings, these observations indicate that selective enhancement of attended AMs in auditory cortex is adaptive under sustained AM-selective attention. This finding has implications for our understanding of cortical mechanisms for feature-based attentional gain control.
Highlights
How can we hear out a sound in an auditory scene? According to contemporary views [1,2], the extraction of a sound of interest from a mixture is facilitated by directing one’s attention toward a distinctive feature of that sound, as this leads to selective enhancement of that feature and temporally coherent features in the cortex relative to unattended features
Previous studies have shown that selective attention to an amplitude modulation (AM) sound enhances the SSR evoked by the AM of that sound, compared with the SSR evoked by a competing, unattended AM sound with distinct tone frequency or location [10,11,12,13]
We observed an enhancement of temporal AM-frequency representations likely located in auditory cortex (AC) during sustained auditory attention relative to visual attention, consistent with previous findings [15,16,17,18]
Summary
According to contemporary views [1,2], the extraction of a sound of interest from a mixture is facilitated by directing one’s attention toward a distinctive feature of that sound, as this leads to selective enhancement of that feature and temporally coherent features in the cortex relative to unattended features Evidence for such a topdown, feature-based gain control mechanism comes from several human brain studies showing that selective attention to a specific tone frequency or a specific location enhances neural responses to sounds that comprise the attended frequency or originate from the attended location, respectively [3,4,5,6,7,8,9]. Considering that AM has been suggested to be encoded in AM-frequency specific channels [21,22] in the auditory cortex (AC) [23,24] and earlier processing stages [25,26,27,28], these findings may suggest that attentional gain control operates on temporal AM representations in AC
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