Abstract
Directing attention to sounds of different frequencies allows listeners to perceive a sound of interest, like a talker, in a mixture. Whether cortically generated frequency-specific attention affects responses as low as the auditory brainstem is currently unclear. Participants attended to either a high- or low-frequency tone stream, which was presented simultaneously and tagged with different amplitude modulation (AM) rates. In a replication design, we showed that envelope-following responses (EFRs) were modulated by attention only when the stimulus AM rate was slow enough for the auditory cortex to track—and not for stimuli with faster AM rates, which are thought to reflect ‘purer’ brainstem sources. Thus, we found no evidence of frequency-specific attentional modulation that can be confidently attributed to brainstem generators. The results demonstrate that different neural populations contribute to EFRs at higher and lower rates, compatible with cortical contributions at lower rates. The results further demonstrate that stimulus AM rate can alter conclusions of EFR studies.
Highlights
Understanding spoken language in the presence of other background sounds requires listeners to direct attention flexibly to distinguishing acoustic characteristics, an ability likely underpinned by dynamic interactions between basic auditory and higher-level cognitive processes (Carlyon et al 2001; Davis and Johnsrude 2007; Billig et al 2013)
We showed that envelope-following responses (EFRs) were modulated by attention only when the stimulus amplitude modulation (AM) rate was slow enough for the auditory cortex to track—and not for stimuli with faster AM rates, which are thought to reflect ‘purer’ brainstem sources
At lower rates (Experiment 1), EFRs were larger and showed stronger phase coherence when listeners were attending to the tone stream that was tagged with that AM rate, compared to when they were attending to the other tone stream
Summary
Understanding spoken language in the presence of other background sounds requires listeners to direct attention flexibly to distinguishing acoustic characteristics (e.g. the fundamental frequency of someone’s voice), an ability likely underpinned by dynamic interactions between basic auditory and higher-level cognitive processes (Carlyon et al 2001; Davis and Johnsrude 2007; Billig et al 2013). Whether directing attention to particular sound frequencies alters processing at the earliest stages of the auditory system is unclear. Improving knowledge of how attention changes the representation of sounds at different stages of auditory processing is fundamental to understanding how listeners hear a sound of interest among a mixture of competing sounds. Whether top-down projections enable filtering of HOLMES ET AL.: Attentional Modulation of Envelope-Following Responses responses at lower stages of the auditory pathway, potentially facilitating perceptual segregation of sounds of different frequencies, is unclear. Descending anatomical projections from the cortex to the cochlea are, at least broadly, organised by frequency (Winer and Schreiner 2005), so it is anatomically plausible that attending to particular frequencies may enhance tuning or gain in a frequency-specific fashion at the earliest levels of auditory processing. Ongoing tuning of brainstem processing based on expectations and goals would permit auditory processing to rapidly adapt to changes in listening environment and would allow listeners to flexibly enhance processing of target sounds
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