Auditory-motor synchronization facilitates attention allocation.

Temporal predictability of auditory events induces larger P300 amplitudes and shorter P300 latencies compared to stimulus presentation with variable onset asynchronies. This suggests that periodic stimuli lead to neuronal entrainment resulting in a more efficient allocation of attentional resources. Simultaneous synchronized motor activity should facilitate the precise temporal encoding of acoustic sequences. Therefore the current event-related potential study investigated whether embodied stimulus encoding enhances the reported effects of stimulus periodicity. We found that simultaneous pedaling on an ergometer compared to a physically passive situation amplified the predictability effect on the P300 component. Furthermore, the temporal variability of cycling behavior correlated positively with both P300 latency and P300 amplitude. These findings indicate that auditory-motor synchronization enhances the attentional processing of periodical auditory stimuli.

P3b reflects periodicity in linguistic sequences.

Temporal predictability is thought to affect stimulus processing by facilitating the allocation of attentional resources. Recent studies have shown that periodicity of a tonal sequence results in a decreased peak latency and a larger amplitude of the P3b compared with temporally random, i.e., aperiodic sequences. We investigated whether this applies also to sequences of linguistic stimuli (syllables), although speech is usually aperiodic. We compared aperiodic syllable sequences with two temporally regular conditions. In one condition, the interval between syllable onset was fixed, whereas in a second condition the interval between the syllables' perceptual center (p-center) was kept constant. Event-related potentials were assessed in 30 adults who were instructed to detect irregularities in the stimulus sequences. We found larger P3b amplitudes for both temporally predictable conditions as compared to the aperiodic condition and a shorter P3b latency in the p-center condition than in both other conditions. These findings demonstrate that even in acoustically more complex sequences such as syllable streams, temporal predictability facilitates the processing of deviant stimuli. Furthermore, we provide first electrophysiological evidence for the relevance of the p-center concept in linguistic stimulus processing.

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

Frequency modulations (FM) play a decisive role in our everyday communication. To investigate the processing of FM direction we measured change-related auditory cortex responses with human magnetoencephalography. First, we tested for FM direction selectivity by presenting FM sweeps with the same FM directions in a repeated series (RS). These series were interrupted by a deviant with the opposite FM direction. Second, we tested for the representation of abstract rules and presented series of FM sweeps with alternating FM directions (AS). The AS series were interrupted by a deviant which was a repetition of the series' last FM sweep but broke the alternating pattern. For the RS, the deviant did not evoke significant change-related responses in the auditory cortex. However, for the first stimulus after the deviant, significantly stronger responses compared to standards were observed bilaterally in the auditory cortex at about 200 ms after stimulus onset. For the AS, we observed a similar bilateral change-related signal enhancement for a deviant FM sweep breaking the alternating series. Since this response enhancement occurred for both RS and AS even after a single FM sweep repetition, we conclude that these activities represent local signal enhancements rather than change-related responses due to abstract rule violation. In sum, our data indicate repetition enhancement due to spectro-temporal interactions between successive complex FM sweeps. These enhancement effects were observed for the first but not further repetitions suggesting a second-order repetition suppression of the initial repetition enhancement.

Auditory repetition enhancement at short interstimulus intervals for frequency-modulated tones.

Frequency-modulated (FM) sweeps are important components of most natural sounds. To examine the processing of these stimuli we applied a two-tone paradigm. Repeated stimulus presentation usually leads to reduced neuronal responses. However, in a former study repetition enhancements which have been observed when FM tones were separated by short interstimulus intervals (ISIs) of ≤200ms. To further investigate this repetition effect in response to FM tones, we recorded magnetoencephalogram (MEG) in humans during the presentation of consecutive FM sweep pairs separated by ISIs between 100 and 600ms. We presented FM sweep pairs in six experimental conditions: a) two upward FM tones, b) two downward FM tones, c) an upward followed by a downward FM tone and d) a downward followed by an upward FM tone. Sequences of single upward and single downward FM tones served as control conditions. N1m amplitude was enhanced for repeated compared with different FM-direction tone pairs. This effect was found for the shortest ISI of 100ms and disappeared at longer ISIs. Furthermore, mean peak latencies in response to the second tone were prolonged in same-direction pairs at the shortest ISI of 100ms. At ISIs ≥300ms slight enhancement effects occurred between 180 and 400ms after the second stimulus. This is in accordance with a previous MEG study from our laboratory which demonstrated an enhancement effect for sustained fields at latencies of 150-350ms after the second stimulus for same compared to different FM tone pairs separated by an ISI of 200ms.

Repetition enhancement for frequency-modulated but not unmodulated sounds: a human MEG study.

BACKGROUND: Decoding of frequency-modulated (FM) sounds is essential for phoneme identification. This study investigates selectivity to FM direction in the human auditory system. METHODOLOGY/PRINCIPAL FINDINGS: Magnetoencephalography 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/SIGNIFICANCE: Low-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.