Noise‐induced increase in human auditory evoked neuromagnetic fields

Abstract

Noise is usually detrimental to auditory perception. However, recent psychophysical studies have shown that low levels of broadband noise may improve signal detection. Here, we measured auditory evoked fields (AEFs) while participants listened passively to low-pitched and high-pitched tones (Experiment 1) or complex sounds that included a tuned or a mistuned component that yielded the perception of concurrent sound objects (Experiment 2). In both experiments, stimuli were embedded in low or intermediate levels of Gaussian noise or presented without background noise. For each participant, the AEFs were modeled with a pair of dipoles in the superior temporal plane, and the effects of noise were examined on the resulting source waveforms. In both experiments, the N1m was larger when the stimuli were embedded in low background noise than in the no-noise control condition. Complex sounds with a mistuned component generated an object-related negativity that was larger in the low-noise condition. The results show that low-level background noise facilitates AEFs associated with sound onset and can be beneficial for sorting out concurrent sound objects. We suggest that noise-induced increases in transient evoked responses may be mediated via efferent feedback connections between the auditory cortex and lower auditory centers.

Neural generators underlying concurrent sound segregation

“…Bilateral ORNm sources were found with peak activity in the 135 to 175 ms latency interval previously reported for this data set (Alain et al, 2009 …”

“…ER-SAM analysis was applied to two previous MEG data sets ( [Alain et al, 2009] and [Alain and McDonald, 2007]). …”

“…It is well known in the field of event-related potentials that the onset of a sound is associated with an obligatory -P1-N1-P2‖ long-latency response beginning around 50 ms after the sound has been perceived ( [Knight et al, 1980] and [Näätänen and Picton, 1987]). Accordingly, it is possible that the ORN component may itself be a manifestation of a temporally delayed P1, N1, and/or P2 in response to the detection of the mistuned harmonic ( [Alain et al, 2001], [Alain and McDonald, 2007] and [Alain et al, 2009]). The plausibility of this -delayed onset‖ hypothesis is bolstered by dipole source localization studies that place the neural generators of these P1, N1 and P2 responses in regions (Hari et al, 1987) proximal to where the ORN is believed to occur (i.e., the Sylvian fissure).…”

“…In the present study, we sought to localize generators of the ORN as well as the obligatory onset response by applying event-related synthetic aperture magnetometry (ER-SAM; and [Robinson and Vrba, 2004]) to two mistuned harmonic MEG data sets ( [Alain and McDonald, 2007] and [Alain et al, 2009]). Unlike ECD source modeling, the ER-SAM algorithm does not require a priori assumptions about the number or location of sources (e.g., basing the ORN model on an N1 source).…”

“…Selection of evoked field components and time points was guided by the auditory evoked field MEG data previously reported for these data sets ( [Alain and McDonald, 2007] and [Alain et al, 2009]). In those studies, the P1m, N1m and P2m evoked fields were found to peak around 66 ms, 115 ms, 180 ms (Experiment 1) and 53 ms, 109 ms, 197 ms (Experiment 2), respectively.…”