Cross-modal attentional effects of rhythmic sensory stimulation

Rhythm-based Temporal Expectations: Unique Contributions of Predictability and Periodicity

Anticipating events and focusing attention accordingly are crucial for navigating our dynamic environment. Rhythmic patterns of sensory input offer valuable cues for temporal expectations and facilitate perceptual processing. Rhythm-based temporal expectations may rely on oscillatory entrainment, where neural activity and perceptual sensitivity synchronize with periodic stimuli. However, whether entrainment models can account for aperiodic predictable rhythms remains unclear. Our study aimed to delineate the distinct roles of predictability and periodicity in rhythm-based expectations. Participants performed a pitch-identification task preceded by periodic predictable, aperiodic predictable, or aperiodic unpredictable temporal sequences. By manipulating the temporal position of the target sound, we observed how auditory perceptual performance was modulated by the target position's relative phase relationship to the preceding sequences. Results revealed a significant performance advantage for predictable sequences, both periodic and aperiodic, compared with unpredictable ones. However, only the periodic sequence induced an entrained modulation pattern, with performance peaking in synchrony with the inherent sequence continuation. Event-related brain potentials corroborated these findings. The target-evoked P3b, possibly a neural marker of attention allocation, mirrored the behavioral performance patterns. This supports our hypothesis that temporal attention guided by rhythm-based expectations modulates perceptual performance. Furthermore, the predictive sequences were associated with enhanced target-preceding negativity (akin to the contingent negative variation), indicating enhanced target preparation. The periodic-specific modulation likely reflects more precise temporal expectations, potentially involving neural entrainment and/or more focused attention. Our findings suggest that predictability and periodicity influence perception through distinct mechanisms.

Reliable quantification of neural entrainment to rhythmic auditory stimulation: simulation and experimental validation

Objective.Entrainment has been considered as a potential mechanism underlying the facilitatory effect of rhythmic neural stimulation on neurorehabilitation. The inconsistent effects of brain stimulation on neurorehabilitation found in the literature may be caused by the variability in neural entrainment. To dissect the underlying mechanisms and optimize brain stimulation for improved effectiveness, it is critical to reliably assess the occurrence and the strength of neural entrainment. However, the factors influencing entrainment assessment are not yet fully understood. This study aims to investigate whether and how the relevant factors (i.e. data length, frequency bandwidth, signal-to-noise ratio (SNR), center frequency, and the constant component of stimulus-response phase-difference) influence the assessment reliability of neural entrainment.Approach.We simulated data for 28 scenarios to answer above questions. We also recorded experimental data to verify the findings from our simulation study.Main results.A minimal data length is required to achieve reliable neural entrainment assessment, and this requirement critically depends on the bandwidth and SNR, but is independent of the center frequency and the constant component of stimulus-response phase-difference. Furthermore, changing of bandwidth is accompanied by the change of SNR.Significance.The present study has revealed how data length, bandwidth, and SNR critically affect the assessment reliability of neural entrainment. The findings provide a foundation for the parameter setting in experiment design and data analysis in neural entrainment studies. While this study is within the context of rhythmic auditory stimulation, the conclusions may be applicable for neural entrainment to other rhythmic stimulations.

Physiological Entrainment: A Key Mind-Body Mechanism for Cognitive, Motor and Affective Functioning, and Well-Being

BACKGROUND

The human sensorimotor system can naturally synchronize with environmental rhythms, such as light pulses or sound beats. Several studies showed that different styles and tempos of music, or other rhythmic stimuli, have an impact on physiological rhythms, including electrocortical brain activity, heart rate, and motor coordination. Such synchronization, also known as the "entrainment effect", has been identified as a crucial mechanism impacting cognitive, motor, and affective functioning.

OBJECTIVES

This review examines theoretical and empirical contributions to the literature on entrainment, with a particular focus on the physiological mechanisms underlying this phenomenon and its role in cognitive, motor, and affective functions. We also address the inconsistent terminology used in the literature and evaluate the range of measurement approaches used to assess entrainment phenomena. Finally, we propose a definition of "physiological entrainment" that emphasizes its role as a fundamental mechanism that encompasses rhythmic interactions between the body and its environment, to support information processing across bodily systems and to sustain adaptive motor responses.

METHODS

We reviewed the recent literature through the lens of the "embodied cognition" framework, offering a unified perspective on the phenomenon of physiological entrainment.

RESULTS

Evidence from the current literature suggests that physiological entrainment produces measurable effects, especially on neural oscillations, heart rate variability, and motor synchronization. Eventually, such physiological changes can impact cognitive processing, affective functioning, and motor coordination.

CONCLUSIONS

Physiological entrainment emerges as a fundamental mechanism underlying the mind-body connection. Entrainment-based interventions may be used to promote well-being by enhancing cognitive, motor, and affective functions, suggesting potential rehabilitative approaches to enhancing mental health.

Testing the impact of hatha yoga on task switching: a randomized controlled trial

Switching attention between or within tasks is part of the implementation and maintenance of executive control processes and plays an indispensable role in our daily lives: It allows us to perform on distinct tasks and with variable objects, enabling us to adapt to and respond in dynamically changing environments. Here, we tested if yoga could benefit switching of attention between distinct objects of one’s focus (e.g., through practicing switching between one’s own body, feelings, and different postures) in particular and executive control in general. We therefore conducted a randomized controlled trial with 98 participants and a waitlisted control group. In the intervention group, healthy yoga novices practiced Hatha yoga 3x a week, for 8 weeks. We conducted two experiments: A purely behavioral task investigating changes in behavioral costs during switching between attentional control sets (74 participants analyzed), and a modality-switching task focusing on electrophysiology (EEG data of 47 participants analyzed). At the electrophysiological level, frequency-tagging indicated no interventional effect on participants’ ability to switch between the auditory and visual modalities. However, increases in task-related frontocentral theta activity, resulting from the intervention, indicated an ability to increasingly deploy executive resources to the prioritized task when needed. At the behavioral level, our intervention resulted in more efficient holding of target representations in working memory, indicated by decreased mixing costs. Again, however, intervention effects on switching costs were missing. We, thus, conclude that Hatha yoga has a positive influence on executive control, potentially through improvements in working memory rather than directly on switching.

Clinical trial registration

clinicaltrials.gov, identifier [NCT05232422].

Influence of rhythmic contexts on perception: No behavioral and eye-tracker evidence for rhythmic entrainment

Entrainment theories propose that attention inherently oscillates between moments of attentional enhancement and disengagement. Consequently, perceptual and response benefits have been reported in tasks with a rhythmic structure. In the present study, we report two preregistered auditory experiments attempting to replicate previous supporting behavioral evidence of entrainment theories. In addition, we incorporated eye-tracker measures. Both Experiment 1 (duration discrimination task) and Experiment 2 (pitch discrimination task) showed no phase-specific benefit of rhythmic sequences compared to arrhythmic ones. Importantly, a tonic larger pupil size for arrhythmic conditions was observed irrespective of target phase, suggesting higher processing demands or arousal state imposed by a sustained uncertain context. Overall, the present results call into question whether the perceptual benefits predicted by entrainment theories are generalizable across all experimental designs and paradigms. On the contrary, our findings join a large group of studies that have failed to replicate the foundational results of attentional entrainment.

Enhancing rhythmic temporal expectations: The dominance of auditory modality under spatial uncertainty

To effectively process the most relevant information, the brain anticipates the optimal timing for allocating attentional resources. Behavior can be optimized by automatically aligning attention with external rhythmic structures, whether visual or auditory. Although the auditory modality is known for its efficacy in representing temporal information, the current body of research has not conclusively determined whether visual or auditory rhythmic presentations have a definitive advantage in entraining temporal attention. The present study directly examined the effects of auditory and visual rhythmic cues on the discrimination of visual targets in Experiment 1 and on auditory targets in Experiment 2. Additionally, the role of endogenous spatial attention was also considered. When and where the target was the most likely to occur were cued by unimodal (visual or auditory) and bimodal (audiovisual) signals. A sequence of salient events was employed to elicit rhythm-based temporal expectations and a symbolic predictive cue served to orient spatial attention. The results suggest a superiority of auditory over visual rhythms, irrespective of spatial attention, whether the spatial cue and rhythm converge or not (unimodal or bimodal), and regardless of the target modality (visual or auditory). These findings are discussed in terms of a modality-specific rhythmic orienting, while considering a single, supramodal system operating in a top-down manner for endogenous spatial attention.

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.

10 Hz rhythmic stimulation modulates electrophysiological, but not behavioral markers of suppression

We investigated the role of alpha in the suppression of attention capture by salient but to-be-suppressed (negative and nonpredictive) color cues, expecting a potential boosting effect of alpha-rhythmic entrainment on feature-specific cue suppression. We did so by presenting a rhythmically flickering visual bar of 10 Hz before the cue - either on the cue's side or opposite the cue -while an arrhythmically flickering visual bar was presented on the respective other side. We hypothesized that rhythmic entrainment at cue location could enhance the suppression of the cue. Testing 27 participants ranging from 18 to 39 years of age, we found both behavioral and electrophysiological evidence of suppression: Search times for a target at a negatively cued location were delayed relative to a target away from the cued location (inverse validity effects). In addition, an event-related potential indicative for suppression (the Distractor Positivity, Pd) was observed following rhythmic but not arrhythmic stimulation, indicating that suppression was boosted by the stimulation. This was also echoed in higher spectral power and intertrial phase coherence of EEG at rhythmically versus arrhythmically stimulated electrode sites, albeit only at the second harmonic (20 Hz), but not at the stimulation frequency. In addition, inverse validity effects were not modulated by rhythmic entrainment congruent with the cue side. Hence, we propose that rhythmic visual stimulation in the alpha range could support suppression, though behavioral evidence remains elusive, in contrast to electrophysiological findings.

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.