Regular Tone Research Articles

Carrier-frequency specific omission-related neural activity in ordered sound sequences is independent of omission-predictability.

Regularities in our surroundings lead to predictions about upcoming events. Previous research has shown that omitted sounds during otherwise regular tone sequences elicit frequency-specific neural activity related to the upcoming but omitted tone. We tested whether this neural response is depending on the unpredictability of the omission. Therefore, we recorded magnetencephalography (MEG) data while participants listened to ordered or random tone sequences with omissions occurring either ordered or randomly. Using multivariate pattern analysis shows that the frequency-specific neural pattern during omission within ordered tone sequences occurs independent of the regularity of the omissions. These results suggest that the auditory predictions based on sensory experiences are not immediately updated by violations of those expectations.

Effects of temporally regular versus irregular distractors on goal-directed cognition and behavior

Human environments comprise plenty of task-irrelevant sensory inputs, which are potentially distracting. Auditory distractors often possess an inherent temporal structure. However, it is largely unknown whether and how the temporal regularity of distractors interferes with goal-directed cognitive processes, such as working memory. Here, we tested a total sample of N = 90 participants across four working memory tasks with sequences of temporally regular versus irregular distractors. Temporal irregularity was operationalized by a final tone onset time that violated an otherwise regular tone sequence (Experiment 1), by a sequence of tones with irregular onset-to-onset delays (Experiment 2), and by sequences of speech items with irregular onset-to-onset delays (Experiments 3 and 4). Across all experiments, temporal regularity of distractors did not modulate participants’ primary performance metric, that is, accuracy in recalling items from working memory. Instead, temporal regularity of distractors modulated secondary performance metrics: for regular versus irregular distractors, recall of the first item from memory was faster (Experiment 3) and the response bias was more conservative (Experiment 4). Taken together, the present results provide evidence that the temporal regularity of task-irrelevant input does not inevitably affect the precision of memory representations (reflected in the primary performance metric accuracy) but rather the response behavior (reflected in secondary performance metrics like response speed and bias). Our findings emphasize that a comprehensive understanding of auditory distraction requires that existing models of attention include often-neglected secondary performance metrics to understand how different features of auditory distraction reach awareness and impact cognition and behavior.

Cortical networks for auditory detection with and without informational masking: Task effects and implications for conscious perception

Ambiguous and masked stimuli have been used to study conscious perception by comparing neural activity during different percepts of identical physical stimuli. One limitation of this approach is that it typically requires a reporting task that may engage neural processes beyond those required for conscious perception. Here, we explored potential fMRI correlates of auditory conscious perception with and without overt report. In experiment 1, regular tone patterns were presented as targets under informational masking, and participants reported their percepts on each trial. In experiment 2, regular tone patterns were presented without masking, while the uninformed participants (i) passively fixated, (ii) performed an orthogonal visual task, and (iii) reported trial-wise the presence of the auditory pattern as in experiment 1 (in fixed order). Under informational masking, target-pattern detection was associated with activity in auditory cortex, superior temporal sulcus, and a distributed fronto-parieto-insular network. Unmasked and task-irrelevant tone patterns elicited activity that overlapped with the network observed under informational masking in auditory cortex, the right superior temporal sulcus, and the ventral precentral sulcus in an ROI analysis. We therefore consider these structures candidate regions for a neural substrate of auditory conscious perception. In contrast, activity in the intraparietal sulcus, insula, and dorsal precentral sulcus were only observed for unmasked tone patterns when they were task relevant. These areas therefore appear more closely related to task performance or top-down attention rather than auditory conscious perception, per se.

Auditory-induced bouncing is a perceptual (rather than a cognitive) phenomenon: Evidence from illusory crescents

A central task for vision is to identify objects as the same persisting individuals over time and motion. The need for such processing is made especially clear in ambiguous situations such as the bouncing/streaming display: two discs move toward each other, superimpose, and then continue along their trajectories. Did the discs stream past each other, or bounce off each other? When people are likely to perceive streaming, playing a brief tone at the moment of overlap can readily cause them to see bouncing instead. Recent research has attributed this effect to decisional (rather than perceptual) processes by showing that auditory tones alter response biases but not the underlying sensitivity for detecting objective bounces. Here we explore the nature of this phenomenon using ‘illusory causal crescents’: when people perceive bouncing (or causal ‘launching’), they also perceive the second disc to begin moving before being fully overlapped with the first disc (i.e. leaving an uncovered crescent). Here we demonstrate that merely playing a sound coincident to the moment of overlap can also reliably induce the perception of such illusory crescents. Moreover, this effect is due to the coincidence of the tone, per se, since the effect disappears when the tone is embedded in a larger regular tone sequence. Because observers never have to explicitly categorize their percept (e.g. as streaming)—and because the effect involves a subtle quantitative influence on another clearly visual property (i.e. the crescent’s width)—we conclude that this audiovisual influence on the perception of identity over time reflects perceptual processing rather than higher-level decisions.

Stimulus phase locking of cortical oscillation for perceptual organization

The phase of cortical oscillations contains rich information and is valuable for encoding sound stimuli. We tested whether and how spatial patterns of oscillatory phase locking within the auditory cortex better predicted perceptual organization than those of response amplitude. A high-density microelectrode array with 10 × 10 sites within 4 × 4 mm2 mapped LFPs at the 4th layer of auditory cortex in rats. First, in response to ABA-sequences with different inter-tone intervals and frequency differences, neurometric functions based on stimulus phase locking in the gamma band could better describe van Noorden’s perceptual boundary than the LFP amplitude. Second, when a random tone sequence was switched to a regular tone sequence, the gamma-band phase locking increased immediately after the transition from random to regular sequences. The amplitude of the tone-evoked response, on the other hand, increased with frequency separation with respect to the prior tone, irrespective of putative organization of auditory objects. These results suggest that the evoked-response amplitude encodes the local order of tones, while the phase locking better predicts the perceptual organization.

Contingent negative variation (CNV) associated with sensorimotor timing error correction

IntroductionDetection and subsequent correction of sensorimotor timing errors are fundamental to adaptive behavior. Using scalp-recorded event-related potentials (ERPs), we sought to find ERP components that are predictive of error correction performance during rhythmic movements. MethodHealthy right-handed participants were asked to synchronize their finger taps to a regular tone sequence (every 600ms), while EEG data were continuously recorded. Data from 15 participants were analyzed. Occasional irregularities were built into stimulus presentation timing: 90ms before (advances: negative shift) or after (delays: positive shift) the expected time point. A tapping condition alternated with a listening condition in which identical stimulus sequence was presented but participants did not tap. ResultsBehavioral error correction was observed immediately following a shift, with a degree of over-correction with positive shifts. Our stimulus-locked ERP data analysis revealed, 1) increased auditory N1 amplitude for the positive shift condition and decreased auditory N1 modulation for the negative shift condition; and 2) a second enhanced negativity (N2) in the tapping positive condition, compared with the tapping negative condition. In response-locked epochs, we observed a CNV (contingent negative variation)-like negativity with earlier latency in the tapping negative condition compared with the tapping positive condition. This CNV-like negativity peaked at around the onset of subsequent tapping, with the earlier the peak, the better the error correction performance with the negative shifts while the later the peak, the better the error correction performance with the positive shifts. DiscussionThis study showed that the CNV-like negativity was associated with the error correction performance during our sensorimotor synchronization study. Auditory N1 and N2 were differentially involved in negative vs. positive error correction. However, we did not find evidence for their involvement in behavioral error correction. Overall, our study provides the basis from which further research on the role of the CNV in perceptual and motor timing can be developed.

Spontaneous Motor Tempo is the Easiest Pace to Act Upon for Both the Emergent and the Predictive Timing Modes

Spontaneous Motor Tempo is the Easiest Pace to Act Upon for Both the Emergent and the Predictive Timing Modes

Event-related potential correlates of sound organization: Early sensory and late cognitive effects

We tested whether incoming sounds are processed differently depending on how the preceding sound sequence has been interpreted by the brain. Sequences of a regularly repeating three-tone pattern, the perceived organization of which spontaneously switched back and forth between two alternative interpretations, were delivered to listeners. Occasionally, a regular tone was exchanged for a slightly or moderately lower one (deviants). The electroencephalogram (EEG) was recorded while listeners continuously marked their perception of the sound sequence. We found that for both the regular and the deviant tones, the early exogenous P1 and N1 amplitudes varied together with the perceived sound organization. Percept-dependent effects on the late endogenous N2 and P3a amplitudes were only found for deviant tones. These results suggest that the perceived sound organization affects sound processing both by modulating what information is extracted from incoming sounds as well as by influencing how deviant sound events are evaluated for further processing.

Functional lateralization in auditory cortex under informational masking and in silence

The N(1) m is an evoked magnetic field in auditory cortex that is automatically elicited by tones in silence but not in the context of multiple other tones: when listeners are unaware of a tone stream because of informational masking, no N(1) m-like activity is observed. In contrast, N(1) m-like activity is evoked when listeners are aware of the regular tone stream in the same context but in another trial. Here we compared this awareness-related negativity (ARN) with the automatic N(1) m. First, we evaluated whether stimulus lateralization by ear or interaural time differences modulates hemispheric lateralization of the response, as a putative marker of sensory processing. Second, we evaluated the stimulus-independent hemispheric balance thought to indicate higher level cortical processing. The results dissociate three, partly overlapping, time intervals: the P(1) m (45-85 ms) was evoked by missed and detected target tones alike. Subsequent negative activity was only observed when listeners indicated awareness of the target stream inside the multi-tone masker. In the N(1) m time interval (75-175 ms), hemispheric balance of the ARN and N(1) m was modulated by stimulus lateralization. In the subsequent time interval (175-275 ms), auditory-cortex activity was generally right-lateralized in silence and balanced under informational masking, but was not modulated by stimulus lateralization. These results suggest that the same auditory-cortex activity that varies with perceptual awareness also shows sensory response features. This is in accordance with models for visual perception, suggesting that sensory competition determines whether midlevel visual responses occur automatically or vary with perceptual state.

Can a regular context induce temporal orienting to a target sound?

It has been shown recently (Lange, 2009) that the N1 of the auditory event related potential (ERP) is attenuated when the eliciting stimulus predictably follows a regular vs. an irregular sequence. This may be a sign of temporal orienting induced by the regular sequence. Alternatively, the attenuated N1 may have been due to sensory predictability of target timing. The present study investigated whether presenting a regular sequence still attenuates target N1 when target timing is unpredictable. A regular (vs. irregular) tone sequence was presented prior to a target tone, which appeared unpredictably at one of three different time points after the sequence. For the regular sequence, targets either continued regularity (on-time targets) or were early or late with respect to this regular time point. ERPs to on-time targets were compared as a function of sequence regularity. Consistent with the assumption that N1 attenuation reflects sensory predictability of target timing, an attenuated N1 was not observed in the present study, where target timing was uncertain.

Cholinergic Deafferentation of Prefrontal Cortex Increases Sensitivity to Cross-Modal Distractors during a Sustained Attention Task

The effects of restricted cholinergic deafferentation of prefrontal cortex in rats on sustained attention were assessed. Attentional demands were increased by presentation of distractor stimuli in a different modality (auditory) or the same modality (visual) as target stimuli. Additionally, the effects of the regularity of the distractor on rats' ability to disregard this stimulus were assessed by testing different frequencies of stimuli for each modality. Cholinergically lesioned rats were more sensitive to the effects of auditory distractors than nonlesioned rats, whereas visual distractors of any frequency potently impaired the performance of all subjects. The effects of the auditory stimuli on attentional performance varied depending on the frequency of the tone. A tone with a predictable pattern enhanced signal detection in all rats. An irregular tone selectively impaired performance of rats with cholinergic lesions. Additional tests suggest that rats use the regular tone to time when to attend. Lesioned rats were impaired when the regular tone was presented with a more variable intertrial interval in a subsequent testing session, suggesting impairments in top-down control. In addition to changes in top-down control of attention, differential effects on performance based on the regularity of the tone suggest that stimulus properties encoded by bottom-up processes are also altered after lesioning. The current data suggest that cholinergic deafferentation of prefrontal cortex alters top-down and bottom-up processing of stimuli.

Event-related brain potentials reveal multiple stages in the perceptual organization of sound

Auditory stream segregation has been suggested to include two distinct processing stages: (1) forming representations for alternative organizations of the acoustic input and (2) choosing one organization for perception after weighing the evidence that supports the different alternatives. The current study tested the possibility that auditory event-related potentials (ERP) could be used to index both stages of the stream-segregation process. Sequences of tones that could be perceived either as a single coherent auditory stream (integrated organization) or as two separate streams of sounds (segregated organization) were presented to subjects. The stimulus configuration encouraged perception to fluctuate between these alternative organizations. Subjects were instructed to continuously indicate whether they perceived one or the other organization of the tone sequence. Occasionally, a tone was omitted from the otherwise regular sequence. This deviance was expected to be processed differently depending on the perceptual organization of the sequence at the time of the omission. We found an early ERP response to omission, which was fully determined by parameters of the stimulation and was not sensitive to the perceived sound organization. In contrast, modulation of two ERP components elicited by the regular tone patterns as well as later responses elicited by deviants correlated with the perceived sound organization. These results suggest that sound organization goes through at least two distinct stages, the first being fully stimulus driven, whereas the second is partly under top-down control.

Event-related brain potentials to sound omissions differ in musicians and non-musicians

The mismatch negativity (MMN) component of the auditory event-related brain potential reflects the automatic detection of sound change. MMN to occasionally omitted sounds in a tone series can be used to investigate the time course of temporal integration in the acoustic system. We used MMN to study differences in temporal integration in musicians and non-musicians. In experiment 1, occasionally omitted ‘sounds’ in an otherwise regular tone series evoked a reliable MMN at interstimulus intervals (SOAs) of 100, 120, 180 and 220 ms in musicians. In non-musicians, MMN was smaller/absent in the 180 and 220 ms SOAs, respectively. In experiment 2, deviance of a tone was induced by presenting tones at a shorter SOA (100 or 130 ms) compared to the standard stimulus (150 ms). Musicians showed a reliable MMN for both deviant SOAs whereas non-musicians showed an MMN only for tones presented 50 ms prior to a standard tone (SOA 100 ms). These results indicate that the temporal window of integration seems to be longer and more precise in musicians compared to musical laypersons and that long-term training is reflected in changes in neural activity.

Preattentive periodicity detection in auditory patterns as governed by time and intensity information

The present study demonstrated that the mismatch negativity (MMN), generated by the brain's preattentive detection of a sound change, is elicited by infrequent reversals of two consecutive tones differing in intensity. When tones were presented in a pairwise manner, the MMN was time-locked to the onset of the intensity reversal. When the tones were continuously presented, the MMN was elicited by an irregular loud tone succeeding a regular loud tone but not by an irregular soft tone following a regular soft tone. Results suggest that the preattentive construction of auditory units is primarily governed by the timing of tone presentation but that it may also utilize intensity information, when no sufficient timing information is available.

Regular pulse emission in some megachiropteran bats.

We recorded vocalizations of megachiropteran bats, Cynopterus brachyotis, C. horsfieldi, Megaerops ecaudatus and Macroglossus sobrinus as they were held in our hands, in a hanging position or moved up and down, simulating flight. All four species produced regular audible tone pulses with a frequency spectrum of less than 9 kHz (peak at 4-6 kHz). The duration of a single pulse varied from 14.9 to 23.6 msec on average among these species. The interpulse interval was between 108.3 and 127.7 msec. In M. ecaudatus and M. sobrinus, double pulses were occasionally emitted, with interpulse intervals averaging 39 msec and 31 msec, respectively. The regular pulse emission may indicate that the bats studied use sounds to probe space.