Abstract
Recent evidence has shown top-down modulation of the brainstem frequency following response (FFR), generally in the form of signal enhancement from concurrent stimuli or from switching between attention-demanding task stimuli. However, it is also possible that the opposite may be true – the addition of a task, instead of a resting, passive state may suppress the FFR. Here we examined the influence of a subsequent task, and the relevance of the task modality, on signal clarity within the FFR. Participants performed visual and auditory discrimination tasks in the presence of an irrelevant background sound, as well as a baseline consisting of the same background stimuli in the absence of a task. FFR pitch strength and amplitude of the primary frequency response were assessed within non-task stimulus periods in order to examine influences due solely to general cognitive state, independent of stimulus-driven effects. Results show decreased signal clarity with the addition of a task, especially within the auditory modality. We additionally found consistent relationships between the extent of this suppressive effect and perceptual measures such as response time and proclivity towards one sensory modality. Together these results suggest that the current focus of attention can have a global, top-down effect on the quality of encoding early in the auditory pathway.
Highlights
The auditory brainstem response (ABR) represents some of the earliest encoding of acoustic information within the auditory system, arising from the pooled synchronized response of brainstem neurons
The frequency following response (FFR) component of the ABR represents a phasic, sustained response generally assumed to arise from phase-locking cells within the rostral brainstem projecting into the auditory midbrain, characterized by a frequency profile matching that of the incoming sound [1,2,3,4,5,6,7]
Average signal amplitude within the target frequency (220 Hz) decreased for auditory, but not visual tasks [Figure 2, B, visual, t(16) = 0.14, p..05, auditory, t(16) = 2.31, p,.05], suggesting a suppression of background auditory signals that is more specific to performing an auditory task within this domain. This suppressive effect appears within only the primary frequency range of the background FFR-eliciting tone
Summary
The auditory brainstem response (ABR) represents some of the earliest encoding of acoustic information within the auditory system, arising from the pooled synchronized response of brainstem neurons. Simultaneous presentation of matching visual information with the ABR eliciting acoustic stimuli leads to an enhanced response [8,9,10], with correlated responses at the cortical level [10]. There was an additional background, ongoing ‘‘probe’’ stimulus (1,200 repetitions) used for eliciting the frequency following response (FFR) component of the auditory brainstem response (ABR). Participants were told not to worry about the background tones, and focus only on the primary task. By using this interleaved paradigm of both primary and background tasks, we are able to infer responses to both task relevant and task nonrelevant stimuli. Background tones occurred with a constant ISI in order to minimize distraction from the primary task
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