Repetition Enhancement for Frequency-Modulated but Not Unmodulated Sounds: A Human MEG Study

Abstract

BackgroundDecoding of frequency-modulated (FM) sounds is essential for phoneme identification. This study investigates selectivity to FM direction in the human auditory system.Methodology/Principal FindingsMagnetoencephalography was recorded in 10 adults during a two-tone adaptation paradigm with a 200-ms interstimulus-interval. Stimuli were pairs of either same or different frequency modulation direction. To control that FM repetition effects cannot be accounted for by their on- and offset properties, we additionally assessed responses to pairs of unmodulated tones with either same or different frequency composition. For the FM sweeps, N1m event-related magnetic field components were found at 103 and 130 ms after onset of the first (S1) and second stimulus (S2), respectively. This was followed by a sustained component starting at about 200 ms after S2. The sustained response was significantly stronger for stimulation with the same compared to different FM direction. This effect was not observed for the non-modulated control stimuli.Conclusions/SignificanceLow-level processing of FM sounds was characterized by repetition enhancement to stimulus pairs with same versus different FM directions. This effect was FM-specific; it did not occur for unmodulated tones. The present findings may reflect specific interactions between frequency separation and temporal distance in the processing of consecutive FM sweeps.

Repetition of complex frequency-modulated sweeps enhances neuromagnetic responses in the human auditory cortex

“…To bridge the gap between the response enhancement effects observed for pure tone sequences and complex FM sweeps, future studies could test MEG responses to tone sequences that consist of stimuli derived from a continuum between steady-state harmonic complex tones and harmonic complex FM sweeps. The previously observed MEG response enhancement after a single repetition of an FM sweep at about 200 ms after stimulus onset (Heinemann et al, 2010) is in line with the present findings. However, whereas the enhancements in the previous study occurred for a sustained response with an orientation similar to the N1m, the response enhancements in the present study affected the P2m with opposite orientation.…”

“…The observed amplitude reduction suggested a critical involvement of the P2m component, an evoked magnetic field deflection at about 200 ms after stimulus onset, in the representation of the spectral finestructure of complex sounds. However, in a recent MEG study, we observed repetition enhancement instead of adaptation when the same FM direction was presented consecutively (Heinemann et al, 2010). These findings were obtained employing a two-tone adaptation design with complex FM sweeps and short inter-stimulusintervals (ISI: 200 ms).…”

“…In a previous study employing complex FM glides we reported enhancements after repeated stimulation with the same FM stimulus (Heinemann et al, 2010). These response enhancements occurred during a sustained MEG response from about 200 ms after stimulus onset with an orientation similar to the N1m component.…”

Regularity encoding and deviance detection of frequency modulated sweeps: Human middle‐ and long‐latency auditory evoked potentials

“…A possible explanation of the different results regarding MMN elicitation to FM sounds between our study and Altmann et al (2011) could be due to the differences between the frequency ranges used and the temporal rate at which the stimuli were presented (for a similar argument, see Heinemann et al, 2010). Even though our FM sweeps were designed to soften the transition between consecutive stimuli, the end frequencies and start frequencies among consecutive standard stimuli were always different, whereas the start frequencies of deviant stimuli were always the same as the end frequencies of the preceding standard stimuli.…”

“…Two magnetoencephalographic (MEG) studies showed that the magnetic counterpart of MMN (MMNm) was elicited when a regular presentation of FM glides was violated by a change in the FM direction (i.e., rising vs. falling), suggesting that the auditory system was able to preattentively extract the abstract relationship between frequency transitions (Pardo & Sams, 1993;Sams & Näätänen, 1991). However, by using complex FM sweeps with a Gaussian envelope to control for differences in the initial frequency, two recent MEG studies showed that the processing of complex FM sweeps led to repetition enhancement at short interstimulus intervals (ISIs: Altmann et al, 2011;Heinemann, Rahm, Kaiser, Gaese, & Altmann, 2010), but failed to observe MMNm when the acoustic regularity was violated (Altmann et al, 2011).…”