Rhythmic Modulation of Visual Perception by Continuous Rhythmic Auditory Stimulation

Temporal dependencies in event onsets and event content contain redundant information about musical meter

Musical stimuli present listeners with complex temporal information and rich periodic structure. Periodic patterns in music typically involve multiple hierarchical levels: a basic-level repeating pulse known as the "beat," and a higher-order grouping of beats into the "meter." Previous work has found that a musical stimulus's meter is predicted by recurring temporal patterns of note event onsets, measured by profiles of autocorrelation over time lags. Traditionally, that work has emphasized periodic structure in the timing of event onsets (i.e., repeating rhythms). Here, we suggest that musical meter is in fact a more general perceptual phenomenon, instantiating complex profiles of temporal dependencies across both event onsets and multiple feature dimensions in the actual content of events. We use classification techniques to test whether profiles of temporal dependencies in event onsets and in multiple types of event content predict musical meter. Applying random forest models to three musical corpora, we reproduce findings that profiles of temporal dependencies in note event onsets contain information about meter, but we find that profiles of temporal dependencies in pitch height, interval size, and tonal expectancy also contain such information, with high redundancy among temporal dependencies in event onsets and event content as predictors of meter. Moreover, information about meter is distributed across temporal dependencies at multiple time lags, as indicated by the baseline performance of an unsupervised classifier that selects the single time lag with maximum autocorrelation. Redundant profiles of temporal dependencies across multiple stimulus features may provide strong constraints on musical structure that inform listeners' predictive processes.

Strength of Low-Frequency EEG Phase Entrainment to External Stimuli Is Associated with Fluctuations in the Brain's Internal State

The brain attends to environmental rhythms by aligning the phase of internal oscillations. However, the factors underlying fluctuations in the strength of this phase entrainment remain largely unknown. In the present study, we examined whether the strength of low-frequency electroencephalography (EEG) phase entrainment to rhythmic stimulus sequences varied with the pupil size and posterior alpha-band power, thought to reflect the arousal level and excitability of posterior cortical brain areas, respectively. We recorded the pupil size and scalp EEG while participants carried out an intermodal selective attention task, in which they were instructed to attend to a rhythmic sequence of visual or auditory stimuli and ignore the other perceptual modality. As expected, intertrial phase coherence (ITC), a measure of entrainment strength, was larger for the task-relevant than for the task-irrelevant modality. Across the experiment, the pupil size and posterior alpha power were strongly linked with each other. Interestingly, ITC tracked both variables: larger pupil size was associated with a selective increase in entrainment to the task-relevant stimulus sequence, whereas larger posterior alpha power was associated with a decrease in phase entrainment to both the task-relevant and task-irrelevant stimulus sequences. Exploratory analyses showed that a temporal relation between ITC and posterior alpha power emerged in the time periods around pupil maxima and pupil minima. These results indicate that endogenous sources contribute distinctly to the fluctuations of EEG phase entrainment.

Language switching is modulated by emotion priming: evidence from behavioral and event-related potentials study

Introduction

Bilinguals often switch between different languages to effectively communicate their ideas. The variation in the increase in reaction times and error rates is termed as the language switch cost. Generally, bilingual language-switching costs demonstrate asymmetry, with a greater cost associated with transitioning from the weaker L2 to the dominant L1 than in the reverse scenario. Recent studies have demonstrated that language switching can be modulated under certain conditions. However, the effect of emotion on language-switching performance is unclear. Therefore, this study aimed to investigate the impact of emotions on bilingual language switching and how this impact manifests across different time windows.

Methods

This study explored the influence of emotion on language switching between Chinese (L1) and English (L2) using a dual task involving emotion priming and word-picture matching, with concurrent measurement of event-related potentials.

Results

The behavioral results indicated that a happy mood improved the accuracy and efficiency of L1 switching, while a fearful mood enhanced the efficiency of L2 switching. Electrophysiological data revealed significant interactions among emotion, language, and task in the P1, N2, and N400 stages. Specifically, a happy mood was associated with an increased P1 amplitude during L1 switching, larger N2 amplitudes during L1 repetition, L1 switching, and L2 repetition, as well as greater N400 amplitudes during L1 repetition, L1 switching, and L2 repetition, along with a larger N600 during L2 repetition. Conversely, a fearful mood exhibited a significantly larger N400 during L2 switching and a larger N600 during L2 switching.

Discussion

The study findings suggest that positive emotions were beneficial for L1 switching in the early stages of visual attention allocation, conflict processing, and lexical-semantic processing. In contrast, negative emotions exhibited a more significant advantage for L2 switching in lexical-semantic processing and deeper levels of semantic processing. This study provides the first electrophysiological evidence for the impact of emotion priming on language-switching performance.

Sensory stimulation enhances visual working memory capacity

Visual working memory (vWM) plays a crucial role in visual information processing and higher cognitive functions; however, it has a very limited capacity. Recently, several studies have successfully modulated vWM capacity in humans using entrainment with transcranial alternate current stimulation (tACS) by targeting parietal theta in a frequency-specific manner. In the current study, we aim to expand upon these findings by utilizing sensory instead of electrical stimulation. Across six behavioral experiments (combined N = 209), we applied rhythmic visual and auditory sensory stimulation at 4 Hz and 7 Hz, aiming to modulate vWM capacity. Collectively, the results showed an overall robust improvement with sensory stimulation at either frequency, compared to baseline. However, contrary to our prediction, 7 Hz stimulation tended to slightly outperform 4 Hz stimulation. Importantly, the observed facilitatory effect was mainly driven by the low-capacity sub-group of participants. Follow-up experiments using the Attention Network Test (ANT) and pupillometry measures did not find evidence that this effect could be directly attributed to modulation of phasic or tonic arousal. We speculate that our results differed from those obtained with tACS due to targeting functionally different theta oscillations, or the modulation of participants' temporal expectations.

The phase coherence of cortical oscillations predicts dynamic changes in perceived visibility

The phase synchronization of brain oscillations plays an important role in visual processing, perceptual awareness, and performance. Yet, the cortical mechanisms underlying modulatory effects of post-stimulus phase coherence and frequency-specific oscillations associated with different aspects of vision are still subject to debate. In this study, we aimed to identify the post-stimulus phase coherence of cortical oscillations associated with perceived visibility and contour discrimination. We analyzed electroencephalogram data from two masking experiments where target visibility was manipulated by the contrast ratio or polarity of the mask under various onset timing conditions (stimulus onset asynchronies, SOAs). The behavioral results indicated an SOA-dependent suppression of target visibility due to masking. The time-frequency analyses revealed significant modulations of phase coherence over occipital and parieto-occipital regions. We particularly identified modulations of phase coherence in the (i) 2-5 Hz frequency range, which may reflect feedforward-mediated contour detection and sustained visibility; and (ii) 10-25 Hz frequency range, which may be associated with suppressed visibility through inhibitory interactions between and within synchronized neural pathways. Taken together, our findings provide evidence that oscillatory phase alignments, not only in the pre-stimulus but also in the post-stimulus window, play a crucial role in shaping perceived visibility and dynamic vision.

Multi-timescale neural dynamics for multisensory integration

Carrying out any everyday task, be it driving in traffic, conversing with friends or playing basketball, requires rapid selection, integration and segregation of stimuli from different sensory modalities. At present, even the most advanced artificial intelligence-based systems are unable to replicate the multisensory processes that the human brain routinely performs, but how neural circuits in the brain carry out these processes is still not well understood. In this Perspective, we discuss recent findings that shed fresh light on the oscillatory neural mechanisms that mediate multisensory integration (MI), including power modulations, phase resetting, phase-amplitude coupling and dynamic functional connectivity. We then consider studies that also suggest multi-timescale dynamics in intrinsic ongoing neural activity and during stimulus-driven bottom-up and cognitive top-down neural network processing in the context of MI. We propose a new concept of MI that emphasizes the critical role of neural dynamics at multiple timescales within and across brain networks, enabling the simultaneous integration, segregation, hierarchical structuring and selection of information in different time windows. To highlight predictions from our multi-timescale concept of MI, real-world scenarios in which multi-timescale processes may coordinate MI in a flexible and adaptive manner are considered.

Therapeutic potential of gamma entrainment using sensory stimulation for cognitive symptoms associated with schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with significant morbidity. Treatment options that address the spectrum of symptoms are limited, highlighting the need for innovative therapeutic approaches. Gamma Entrainment Using Sensory Stimulation (GENUS) is an emerging treatment for neuropsychiatric disorders that uses sensory stimulation to entrain impaired oscillatory network activity and restore brain function. Aberrant oscillatory activity often underlies the symptoms experienced by patients with schizophrenia. We propose that GENUS has therapeutic potential for schizophrenia. This paper reviews the current status of schizophrenia treatment and explores the use of sensory stimulation as an adjunctive treatment, specifically through gamma entrainment. Impaired gamma frequency entrainment is observed in patients, particularly in response to auditory and visual stimuli. Thus, sensory stimulation, such as music listening, may have therapeutic potential for individuals with schizophrenia. GENUS holds novel therapeutic potential to improve the lives of individuals with schizophrenia, but further research is required to determine the efficacy of GENUS, optimize its delivery and therapeutic window, and develop strategies for its implementation in specific patient populations.

Long-range and cross-frequency neural modulation of gamma flicker on vigilance decrement

Vigilance decrement is a ubiquitous problem in attention-demanding tasks. Therefore, it is significant to develop neuromodulation methods to mitigate the negative neural effect of vigilance decrement. As one of the non-invasive brain stimulation techniques, visual flicker/rhythmic visual stimulation (RVS) has been proposed to entrain neural oscillations and thereby modulate cognitive processes supported by these brain rhythms, but its effects on vigilance decrement are still unclear. Here, we investigated the effect of gamma flicker on vigilance decrement and its underlying neural mechanism. Thirty participants were recruited to perform a 12-min vigilance task. They were required to discriminate the orientation of lateralized triangle targets with/without 40-Hz RVS background. As a result, it was found that 40-Hz RVS mitigated the decrease in perceptual sensitivity ( A ' ) with time-on-task, a typical adverse effect on behaviors caused by vigilance decrement. Electroencephalography (EEG) results showed that 40-Hz RVS could reduce the significant decline of post-stimulus theta-band inter-trial coherence (ITC) in the prefrontal cortex (PFC) with time-on-task. Regression analysis further revealed that the anterior theta-band ITC was significantly correlated to perceptual sensitivity ( A ' ) in a positive manner. These findings indicated that gamma flicker to the visual cortex had a cross-frequency neuromodulation effect on low-frequency EEG responses over the long-range PFC region. Furthermore, this study provides new insights into the neural effects of 40-Hz RVS, which could impact time-on-task effects on vigilance behaviors and alter the utilization of attentional resources.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-023-10008-6.

Rhythmically Modulating Neural Entrainment during Exposure to Regularities Influences Statistical Learning

The ability to discover regularities in the environment, such as syllable patterns in speech, is known as statistical learning. Previous studies have shown that statistical learning is accompanied by neural entrainment, in which neural activity temporally aligns with repeating patterns over time. However, it is unclear whether these rhythmic neural dynamics play a functional role in statistical learning or whether they largely reflect the downstream consequences of learning, such as the enhanced perception of learned words in speech. To better understand this issue, we manipulated participants' neural entrainment during statistical learning using continuous rhythmic visual stimulation. Participants were exposed to a speech stream of repeating nonsense words while viewing either (1) a visual stimulus with a "congruent" rhythm that aligned with the word structure, (2) a visual stimulus with an incongruent rhythm, or (3) a static visual stimulus. Statistical learning was subsequently measured using both an explicit and implicit test. Participants in the congruent condition showed a significant increase in neural entrainment over auditory regions at the relevant word frequency, over and above effects of passive volume conduction, indicating that visual stimulation successfully altered neural entrainment within relevant neural substrates. Critically, during the subsequent implicit test, participants in the congruent condition showed an enhanced ability to predict upcoming syllables and stronger neural phase synchronization to component words, suggesting that they had gained greater sensitivity to the statistical structure of the speech stream relative to the incongruent and static groups. This learning benefit could not be attributed to strategic processes, as participants were largely unaware of the contingencies between the visual stimulation and embedded words. These results indicate that manipulating neural entrainment during exposure to regularities influences statistical learning outcomes, suggesting that neural entrainment may functionally contribute to statistical learning. Our findings encourage future studies using non-invasive brain stimulation methods to further understand the role of entrainment in statistical learning.

No evidence for tactile entrainment of attention

Temporal patterns in our environment provide a rich source of information, to which endogenous neural processes linked to perception and attention can synchronize. This phenomenon, known as entrainment, has so far been studied predominately in the visual and auditory domains. It is currently unknown whether sensory phase-entrainment generalizes to the tactile modality, e.g., for the perception of surface patterns or when reading braille. Here, we address this open question via a behavioral experiment with preregistered experimental and analysis protocols. Twenty healthy participants were presented, on each trial, with 2 s of either rhythmic or arrhythmic 10 Hz tactile stimuli. Their task was to detect a subsequent tactile target either in-phase or out-of-phase with the rhythmic entrainment. Contrary to our hypothesis, we observed no evidence for sensory entrainment in response times, sensitivity or response bias. In line with several other recently reported null findings, our data suggest that behaviorally relevant sensory phase-entrainment might require very specific stimulus parameters, and may not generalize to the tactile domain.

Attention in flux

Selective attention comprises essential infrastructural functions supporting cognition-anticipating, prioritizing, selecting, routing, integrating, and preparing signals to guide adaptive behavior. Most studies have examined its consequences, systems, and mechanisms in a static way, but attention is at the confluence of multiple sources of flux. The world advances, we operate within it, our minds change, and all resulting signals progress through multiple pathways within the dynamic networks of our brains. Our aim in this review is to raise awareness of and interest in three important facets of how timing impacts our understanding of attention. These include the challenges posed to attention by the timing of neural processing and psychological functions, the opportunities conferred to attention by various temporal structures in the environment, and how tracking the time courses of neural and behavioral modulations with continuous measures yields surprising insights into the workings and principles of attention.

Organization and engagement of a prefrontal-olfactory network during olfactory selective attention

BACKGROUND

Sensory perception is profoundly shaped by attention. Attending to an odor strongly regulates if and how it is perceived - yet the brain systems involved in this process are unknown. Here we report integration of the medial prefrontal cortex (mPFC), a collection of brain regions integral to attention, with the olfactory system in the context of selective attention to odors.

METHODS

First, we used tracing methods to establish the tubular striatum (TuS, also known as the olfactory tubercle) as the primary olfactory region to receive direct mPFC input in rats. Next, we recorded (i) local field potentials from the olfactory bulb (OB), mPFC, and TuS, or (ii) sniffing, while rats completed an olfactory selective attention task.

RESULTS

Gamma power and coupling of gamma oscillations with theta phase were consistently high as rats flexibly switched their attention to odors. Beta and theta synchrony between mPFC and olfactory regions were elevated as rats switched their attention to odors. Finally, we found that sniffing was consistent despite shifting attentional demands, suggesting that the mPFC-OB theta coherence is independent of changes in active sampling.

CONCLUSIONS

Together, these findings begin to define an olfactory attention network wherein mPFC activity, as well as that within olfactory regions, are coordinated based upon attentional states.

Rhythmic modulation of visual discrimination is linked to individuals' spontaneous motor tempo

The impact of external rhythmic structure on perception has been demonstrated across different modalities and experimental paradigms. However, recent findings emphasize substantial individual differences in rhythm-based perceptual modulation. Here, we examine the link between spontaneous rhythmic preferences, as measured through the motor system, and individual differences in rhythmic modulation of visual discrimination. As a first step, we measure individual rhythmic preferences using the spontaneous tapping task. Then we assess perceptual rhythmic modulation using a visual discrimination task in which targets can appear either in-phase or out-of-phase with a preceding rhythmic stream of visual stimuli. The tempo of the preceding stream was manipulated over different experimental blocks (0.77 Hz, 1.4 Hz, 2 Hz). We find that visual rhythmic stimulation modulates discrimination performance. The modulation is dependent on the tempo of stimulation, with maximal perceptual benefits for the slowest tempo of stimulation (0.77 Hz). Most importantly, the strength of modulation is also linked to individuals' spontaneous motor tempo. Individuals with slower spontaneous tempi show greater rhythmic modulation compared to individuals with faster spontaneous tempi. This finding suggests that different tempi affect the cognitive system with varying levels of efficiency and that self-generated rhythms impact our ability to utilize rhythmic structure in the environment for guiding perception and performance.

Sustained responses and neural synchronization to amplitude and frequency modulation in sound change with age

Perception of speech requires sensitivity to features, such as amplitude and frequency modulations, that are often temporally regular. Previous work suggests age-related changes in neural responses to temporally regular features, but little work has focused on age differences for different types of modulations. We recorded magnetoencephalography in younger (21-33 years) and older adults (53-73 years) to investigate age differences in neural responses to slow (2-6 Hz sinusoidal and non-sinusoidal) modulations in amplitude, frequency, or combined amplitude and frequency. Audiometric pure-tone average thresholds were elevated in older compared to younger adults, indicating subclinical hearing impairment in the recruited older-adult sample. Neural responses to sound onset (independent of temporal modulations) were increased in magnitude in older compared to younger adults, suggesting hyperresponsivity and a loss of inhibition in the aged auditory system. Analyses of neural activity to modulations revealed greater neural synchronization with amplitude, frequency, and combined amplitude-frequency modulations for older compared to younger adults. This potentiated response generalized across different degrees of temporal regularity (sinusoidal and non-sinusoidal), although neural synchronization was generally lower for non-sinusoidal modulation. Despite greater synchronization, sustained neural activity was reduced in older compared to younger adults for sounds modulated both sinusoidally and non-sinusoidally in frequency. Our results suggest age differences in the sensitivity of the auditory system to features present in speech and other natural sounds.

Cross-modal attentional effects of rhythmic sensory stimulation

Temporal regularities are ubiquitous in our environment. The theory of entrainment posits that the brain can utilize these regularities by synchronizing neural activity with external events, thereby, aligning moments of high neural excitability with expected upcoming stimuli and facilitating perception. Despite numerous accounts reporting entrainment of behavioural and electrophysiological measures, evidence regarding this phenomenon remains mixed, with several recent studies having failed to provide confirmatory evidence. Notably, it is currently unclear whether and for how long the effects of entrainment can persist beyond their initiating stimulus, and whether they remain restricted to the stimulated sensory modality or can cross over to other modalities. Here, we set out to answer these questions by presenting participants with either visual or auditory rhythmic sensory stimulation, followed by a visual or auditory target at six possible time points, either in-phase or out-of-phase relative to the initial stimulus train. Unexpectedly, but in line with several recent studies, we observed no evidence for cyclic fluctuations in performance, despite our design being highly similar to those used in previous demonstrations of sensory entrainment. However, our data revealed a temporally less specific attentional effect, via cross-modally facilitated performance following auditory compared with visual rhythmic stimulation. In addition to a potentially higher salience of auditory rhythms, this could indicate an effect on oscillatory 3-Hz amplitude, resulting in facilitated cognitive control and attention. In summary, our study further challenges the generality of periodic behavioural modulation associated with sensory entrainment, while demonstrating a modality-independent attention effect following auditory rhythmic stimulation.

Frequency- and Phase-Dependent Effects of Auditory Entrainment on Attentional Blink

Attentional blink (AB) is the impaired detection of a second target (T2) after a first target has been identified. In this paper, we investigated the functional roles of alpha and theta oscillations on AB by determining how much preceding rhythmic auditory stimulation affected the performance of AB. Healthy young adults participated in the experiment online. We found that when two targets were embedded in rapid serial visual presentation (RSVP) of distractors at 10 Hz (i.e., alpha frequency), the magnitude of AB increased with auditory stimuli. The increase was limited to the case when the frequency and phase of auditory stimuli matched the following RSVP stream. On the contrary, when only two targets were presented without a distractor, auditory stimuli at theta, not alpha, increased the AB magnitude. These results indicate that neural oscillations at two different frequencies, namely, alpha and theta, are involved in attentional blink.