Top-down Mechanisms Research Articles

Phasic modulation of beta power at movement-related frequencies during visuomotor conflict.

Rhythmic cortical activity is thought to underlie many cognitive functions including the flexible weighting of sensory information depending on the current behavioral context. Here, we tested for potential oscillatory alignment and power modulation at behaviorally relevant frequencies in magnetoencephalography (MEG) data acquired during a virtual reality-based, rhythmic hand-target phase matching task. The task contained conditions differing in terms of visuomotor incongruence and whether or not behavior (grasping movements) had to be adapted to keep vision aligned with the target. We tested for potential oscillatory alignment with movement frequencies and cross-frequency coupling with oscillations in the alpha, beta, and gamma bands. Our results revealed local peaks at 1 Hz power, corresponding to the frequency at which hand movements alternated between open and close; thus, potentially indicating an "entrainment" of neural oscillations at key movement frequencies. We found 1 Hz power was selectively enhanced when participants needed to align incongruent vision with the target. Moreover, the phase of the "movement-entrained" 1 Hz oscillations coupled significantly with the momentary amplitude of beta band oscillations-again, this coupling was selectively enhanced when incongruent vision was task relevant. We propose that this reflected a top-down mechanism, most likely related to selective attention and rhythmic sensory sampling. Thus, phasic low-frequency (beta) power suppression likely indicated a variable (attentional) sampling of visual movement feedback; i.e., related to increased sensitivity for visually matching alternating hand movements to a phasic target at ecologically important time points, rather than continually during the grasping cycle.NEW & NOTEWORTHY Our results reveal an increased spectral power at movement frequencies in a rhythmic hand-target phase matching task under visuomotor conflict; this effect was strongest when incongruent visual movement feedback was required to guide action. Moreover, the phase of these slow frequencies coupled with the momentary power beta oscillations; again, this coupling was selectively strengthened when incongruent vision was task relevant.

Inferring Attention Shifts for Salient Instance Ranking

AbstractThe human visual system has limited capacity in simultaneously processing multiple visual inputs. Consequently, humans rely on shifting their attention from one location to another. When viewing an image of complex scenes, psychology studies and behavioural observations show that humans prioritise and sequentially shift attention among multiple visual stimuli. In this paper, we propose to predict the saliency rank of multiple objects by inferring human attention shift. We first construct a new large-scale salient object ranking dataset, with the saliency rank of objects defined by the order that an observer attends to these objects via attention shift. We then propose a new deep learning-based model to leverage both bottom-up and top-down attention mechanisms for saliency rank prediction. Our model includes three novel modules: Spatial Mask Module (SMM), Selective Attention Module (SAM) and Salient Instance Edge Module (SIEM). SMM integrates bottom-up and semantic object properties to enhance contextual object features, from which SAM learns the dependencies between object features and image features for saliency reasoning. SIEM is designed to improve segmentation of salient objects, which helps further improve their rank predictions. Experimental results show that our proposed network achieves state-of-the-art performances on the salient object ranking task across multiple datasets. Code and data are available at https://github.com/SirisAvishek/Attention_Shift_Ranks.

The flexibility and representational nature of phonological prediction in listening comprehension: evidence from the visual world paradigm

AbstractUsing the visual world paradigm with printed words, this study investigated the flexibility and representational nature of phonological prediction in real-time speech processing. Native speakers of Mandarin Chinese listened to spoken sentences containing highly predictable target words and viewed a visual array with a critical word and a distractor word on the screen. The critical word was manipulated in four ways: a highly predictable target word, a homophone competitor, a tonal competitor, or an unrelated word. Participants showed a preference for fixating on the homophone competitors before hearing the highly predictable target word. The predicted phonological information waned shortly but was re-activated later around the acoustic onset of the target word. Importantly, this homophone bias was observed only when participants were completing a ‘pronunciation judgement’ task, but not when they were completing a ‘word judgement’ task. No effect was found for the tonal competitors. The task modulation effect, combined with the temporal pattern of phonological pre-activation, indicates that phonological prediction can be flexibly generated by top-down mechanisms. The lack of tonal competitor effect suggests that phonological features such as lexical tone are not independently predicted for anticipatory speech processing.

Spatio-Temporal Feature Pyramid Interactive Attention Network for Egocentric Gaze Prediction

Over the past few years, gaze prediction technology has rapidly developed in human visual attention mechanism research. However, there is still a large gap between the prediction models and the human visual system (HVS). This work makes four contributions to video egocentric gaze prediction research. First, we introduce a new benchmark named ECVG (egocentric video gaze), which consists of 3K high-quality, elaborately selected video sequences spanning a large range of scenes. Existing eye-tracking datasets limit human activities. In contrast, ECVG achieves the collection of eye movement data under real human activity. Second, we establish a visual attention-selection and gaze-tracking model, which summarizes the human visual attention process. Third, we propose a novel feature pyramid interactive attention 3D network (FPIANet) for egocentric gaze prediction, which directly captures the long-term relationship between spatiotemporal features at different time steps and achieves feature nonlocal interactions across temporal, spatial, and scales. In addition, we propose a multiscale interactive attention (MSIA) module, which first explicitly integrates the human top-down and bottom-up visual attention mechanisms to transform any spatiotemporal feature into another feature of the same size but with richer contexts. Furthermore, we propose a new gaze transfer path consistency evaluation and thoroughly examine the performance of our model on two large datasets (ECVG and LEDOV). The experimental results show that our model outperforms the existing state-of-the-art methods.

The Socialist Project on Social Media Platforms: Anticapitalist Organization in Platform Capitalism

This article is a self-reflexive case study of the Socialist Project's (SP) tactical uses of Meta's Facebook and Google's YouTube platforms. Formed in early 2003 by Leo Panitch (1945–2020), Greg Albo, Sam Gindin, Herman Rosenfeld, and others, the SP is a small Toronto-based democratic socialist organization that for nearly two decades has contributed to wider efforts to build and sustain an anticapitalist “infrastructure of dissent” and “radical imagination.” While Facebook's and YouTube's ownership structures, business models, and datafication and commodification mechanisms limit the SP's tactical uses of these platforms, the SP's agency to use these to try to make history in digital conditions not of its own choosing is significant. This article argues that the SP's tactical use of social media platforms exists between structure and agency, at the interface of top-down platform capitalist business models, mechanisms, and logics and bottom-up anticapitalist organization building, public pedagogy, and alternative media making.

Looking at the Local Participation of Coastal Communities in South Java, Indonesia

This study aims to describe the issues and problems of community participation related to the empowerment program entitled PKPT (Development of Strong Coastal Area) in the coastal areas. This study also discusses the importance of creating a participatory development model. This study is essential because PKPT implementation is specific, combining the top-down participation mechanism from the central government with the bottom-up mechanism, namely the northern coastal communities in South Java. The combination of the two mechanisms illustrates the complexity of issues and problems that are not simple because they involve the interests of the central government and the interests of ordinary citizens in coastal areas. Moreover, the focus of this study has yet to be widely studied by previous studies. This study uses a qualitative method applying an action research approach. The informants of the research are organizers of the coastal community, heads of village and village officials, and personnel of the Marine and Fisheries Service of Kebumen Regency in South Java. The result shows that implementing the PKPT program in coastal areas of Java, especially in Kebumen, uses both top-down and bottom-up mechanisms resulting in low participation of the community in the implementation of PKPT substantively. Thus, implicating the lack of sustainability in the empowerment program. This study presents a participatory development model that is expected to be a reference in organizing a sustainable empowerment program for the coastal areas in the future.

International Student Experiences in Three Superdiverse Higher Education Institutions: Institutional Policies and Intersectionalities

Higher education has been facing many challenges due to factors including increased diversification, internationalization, massification, and the expansion of different forms of mobility, which are transforming the landscape of higher education towards “superdiversity”. These challenges are addressed within the framework of “inclusive education”, aiming to increase participation and foster a culture of welcome at higher education institutions. However, scholarly discussions on the ways these initiatives impact the lived experience of students who may face divergent and intersectional forms of exclusion, inequalities, tensions, and discrimination are limited. To address this gap, based on the experience of three participating universities in the European University of Post-Industrial Cities (UNIC) alliance, this paper aims to examine and reflect on the diversity and inclusion practices of the institutions, particularly those targeting concerns for international students with different profiles. Drawing on both existing and emergent data through an extensive case study analysis, the paper focuses on the scope and effectiveness of existing support mechanisms. It concludes that improving the experience of international students and promoting their inclusion at universities requires a combination of top-down and bottom-up mechanisms, as well as centralised and decentralised services. Systematic data collection using a range of engaged research tools also ensures that policies respond to real needs.

Grain Boundary Elimination via Recrystallization-Assisted Vapor Deposition for Efficient and Stable Perovskite Solar Cells and Modules.

Vapor deposition is a promising technology for the mass production of perovskite solar cells. However, the efficiencies of solar cells and modules based on vapor-deposited perovskites are significantly lower than those fabricated using the solution method. Emerging evidence suggests that large defects are generated during vapor deposition owing to a specific top-down crystallization mechanism. Herein, a hybrid vapor deposition method combined with solvent-assisted recrystallization for fabricating high-quality large-area perovskite films with low defect densities is presented. It is demonstrated that an intermediate phase can be formed at the grain boundaries, which induces the secondary growth of small grains into large ones. Consequently, perovskite films with substantially reduced grain boundaries and defect densities are fabricated. Results of temperature-dependent charge-carrier dynamics show that the proposed method successfully suppresses all recombination reactions. Champion efficiencies of 21.9% for small-area (0.16 cm2 ) cells and 19.9% for large-area (10.0 cm2 ) solar modules under AM 1.5 G irradiation are achieved. Moreover, the modules exhibit high operational stability, i.e., they retain >92% of their initial efficiencies after 200h of continuous operation.

China’s Transition to Collective Labor Relations: Top-Down and Bottom-Up Mechanisms

Abstract The article analyzes the development, characteristics, and tendency of China’s labor relations and the labor movement in recent years. It points out that China has begun the transition from individual labor relations to collective labor relations with the strike wave in the summer of 2010 as the main turning point. In the process of transformation, there are two kinds of forces and two ways to accomplish the labor movement. One is the top-down labor union movement led by the authorities within the system; the other is the bottom-up labor movement formed spontaneously by workers outside the system. The article particularly analyzes the emergence of, and mutual relationship between these two types of transition, as well as their influence and significance on China’s labor relations.

Habitat and distribution of the red decorator crab, Schizophrys aspera, a cryptic crown-of-thorns seastar predator

Abstract Cryptic species and their interactions are challenging to describe owing to the difficulties in observing and sampling their populations. Such methodological hurdles are critical to resolve, especially when important interactions involving poorly described species are detected. The red decorator crab, Schizophrys aspera, is a newfound predator of the corallivorous Pacific crown-of-thorns seastar (CoTS; Acanthaster sp.). We discuss the Indo-Pacific distribution and taxonomy of S. aspera and provide characterization of its cryptic population at sites around Heron Island, Great Barrier Reef, that differ in CoTS densities. Most S. aspera (>95%) were found under coral rubble pieces atop existing rubble, associated with large pieces and chasmic interstices. The three smallest individuals (carapace width: 5–11 mm) were found under rubble overlying sand. Mean density of S. aspera was 0.8 ± 0.2 ind. 100 m−2, which varied among sites. Areas with lower records of CoTS had higher densities of S. aspera (p = 0.002; R2 = 0.25), which justifies evaluation of the distribution and impact of this species in context of CoTS outbreaks. We present a method to survey cryptic decapods on coral reefs, along with microhabitat characteristics to help predict S. aspera on reefs prone to CoTS outbreaks and its capacity to act as a natural top-down control mechanism.

Driver's visual fixation attention prediction in dynamic scenes using hybrid neural networks

The traffic driving scenario is dynamically varying and experienced drivers can allocate visual attention effectively in brief time intervals, focusing on prominent targets and areas in advance, thus ensuring safe driving. Therefore, it is significant to research the behavior of driver's visual attention allocation in the development of driver assistance systems and autonomous vehicles. Recently, inspired by top-down and bottom-up attention mechanisms, most visual attention models based on neural networks have been proposed. However, these models tend to yield highly distributed predictions for the specific driving scenario, and have relatively low prediction accuracy, making them unfeasible for being used in practice. Hence, to overcome these challenges, we propose a driver's visual attention model (DVAM) built on the encoder-decoder architecture with the utilization of the convolutional neural network (CNN) and the recurrent neural networks (RNN). Specifically, the model leverages the temporal and spatial dimension information to better mimic realistic dynamic driving, and extract abundant feature information, thus ensuring that the final predictions are authentic and effective. Then, extensive experiments demonstrate that our suggested DVAM achieves better robustness and precision in predicting driver attention to areas or targets compared to state-of-the-art methods on the DR(eye)VE dataset. Finally, our model is deployed on the TDV dataset to validate its generalization capabilities, which prove the potential for field adaptation.

A neural model of modified excitation/inhibition and feedback levels in schizophrenia.

The strength of certain visual illusions, including contrast-contrast and apparent motion, is weakened in individuals with schizophrenia. Such phenomena have been interpreted as the impaired integration of inhibitory and excitatory neural responses, and impaired top-down feedback mechanisms. To investigate whether and how these factors influence the perceived contrast-contrast and apparent motion illusions in individuals with schizophrenia, we propose a two-layer network, with top-down feedback from layer 2 to layer 1 that can model visual receptive fields (RFs) and their inhibitory and excitatory subfields. Our neural model suggests that illusion perception changes in individuals with schizophrenia can be influenced by altered top-down mechanisms and the organization of the on-center off-surround receptive fields. Alteration of the RF inhibitory surround and/or the excitatory center can replicate the difference of illusion precepts between individuals with schizophrenia within certain clinical states and normal controls. The results show that the simulated top-down feedback modulation enlarges the difference of the model illusion representations, replicating the difference between the two groups. We propose that the heterogeneity of visual and in general sensory processing in certain clinical states of schizophrenia can be largely explained by the degree of top-down feedback reduction, emphasizing the critical role of top-down feedback in illusion perception, and to a lesser extent on the imbalance of excitation/inhibition. Our neural model provides a mechanistic explanation for the modulated visual percepts of contrast-contrast and apparent motion in schizophrenia with findings that can explain a broad range of visual perceptual observations in previous studies. The two-layer motif of the current model provides a general framework that can be tailored to investigate subcortico-cortical (such as thalamocortical) and cortico-cortical networks, bridging neurobiological changes in schizophrenia and perceptual processing.

The Role of Word Content, Sentence Information, and Vocoding for Voice Cue Perception.

For voice perception, two voice cues, the fundamental frequency (fo) and/or vocal tract length (VTL), seem to largely contribute to identification of voices and speaker characteristics. Acoustic content related to these voice cues is altered in cochlear implant transmitted speech, rendering voice perception difficult for the implant user. In everyday listening, there could be some facilitation from top-down compensatory mechanisms such as from use of linguistic content. Recently, we have shown a lexical content benefit on just-noticeable differences (JNDs) in VTL perception, which was not affected by vocoding. Whether this observed benefit relates to lexicality or phonemic content and whether additional sentence information can affect voice cue perception as well were investigated in this study. This study examined lexical benefit on VTL perception, by comparing words, time-reversed words, and nonwords, to investigate the contribution of lexical (words vs. nonwords) or phonetic (nonwords vs. reversed words) information. In addition, we investigated the effect of amount of speech (auditory) information on fo and VTL voice cue perception, by comparing words to sentences. In both experiments, nonvocoded and vocoded auditory stimuli were presented. The outcomes showed a replication of the detrimental effect reversed words have on VTL perception. Smaller JNDs were shown for stimuli containing lexical and/or phonemic information. Experiment 2 showed a benefit in processing full sentences compared to single words in both fo and VTL perception. In both experiments, there was an effect of vocoding, which only interacted with sentence information for fo. In addition to previous findings suggesting a lexical benefit, the current results show, more specifically, that lexical and phonemic information improves VTL perception. fo and VTL perception benefits from more sentence information compared to words. These results indicate that cochlear implant users may be able to partially compensate for voice cue perception difficulties by relying on the linguistic content and rich acoustic cues of everyday speech. https://doi.org/10.23641/asha.23796405.

The development of the relationship between auditory and visual neural sensitivity and autonomic arousal from 6 m to 12 m

The differential sensitivity hypothesis argues that environmental sensitivity has the bivalent effect of predisposing individuals to both the risk-inducing and development-enhancing influences of early social environments. However, the hypothesis requires that this variation in environmental sensitivity be general across domains. In this study, we focused on neural sensitivity and autonomic arousal to test domain generality. Neural sensitivity can be assessed by correlating measures of perceptual sensitivity, as indexed by event-related potentials (ERP) in electrophysiology. The sensitivity of autonomic arousal can be tested via heart rate changes. Domain generality was tested by comparing associations in perceptual sensitivity across auditory and visual domains, and associations between sensitivity in sensory domains and heart rate. We contrasted ERP components in auditory (P3) and visual (P1, N290 and P4) detection-of-difference tasks for N = 68 infants longitudinally at 6 and 12 months of age. Domain generality should produce correlated individual differences in sensitivity across the two modalities, with higher levels of autonomic arousal associating with increased perceptual sensitivity. Having controlled for multiple comparisons, at 6 months of age, the difference in amplitude of the P3 component evoked in response to standard and deviant tones correlated with the difference in amplitude of the P1 N290 and P4 face-sensitive components evoked in response to fearful and neutral faces. However, this correlation was not found at 12 months of age. Similarly, autonomic arousal correlated with neural sensitivity at 6 months but not at 12 months. The results suggest bottom-up neural perceptual sensitivity is domain-general across auditory and visual domains and is related to autonomic arousal at 6 months but not at 12 months of age. We interpret the development of the association of these markers of ES within a neuroconstructivist framework and with respect to the concept of interactive specialisation. By 12 months of age, more experience of visual processing may have led to top-down endogenous attention mechanisms that process visual information in a way that no longer associates with automatic auditory perceptual sensitivity.

Top-down control of exogenous attentional selection is mediated by beta coherence in prefrontal cortex

Salience-driven exogenous and goal-driven endogenous attentional selection are two distinct forms of attention that guide selection of task-irrelevant and task-relevant targets in primates. Top-down attentional control mechanisms enable selection of the task-relevant target by limiting the influence of sensory information. Although the lateral prefrontal cortex (LPFC) is known to mediate top-down control, the neuronal mechanisms of top-down control of attentional selection are poorly understood. Here, we trained two rhesus monkeys on a two-target, free-choice luminance-reward selection task. We demonstrate that visual-movement (VM) neurons and nonvisual neurons or movement neurons encode exogenous and endogenous selection. We then show that coherent beta activity selectively modulates mechanisms of exogenous selection specifically during conflict and consequently may support top-down control. These results reveal the VM-neuron-specific network mechanisms of attentional selection and suggest a functional role for beta-frequency coherent neural dynamics in the modulation of sensory communication channels for the top-down control of attentional selection.

Top-down reconfiguration of SMA cortical connectivity during action preparation

The Bereitschaftspotential (BP), a scalp potential recorded in humans during action preparation, is characterized by a slow amplitude increase over fronto-central regions as action execution approaches. We recorded TMS evoked-potentials (TEP) stimulating the supplementary motor area (SMA) at different time-points during a Go/No-Go task to assess whether and how cortical excitability and connectivity of this region change as the BP increases. When approaching BP peak, left SMA reactivity resulted greater. Concurrently, its effective connectivity increased with the left occipital areas, while it decreased with the right inferior frontal gyrus, indicating a fast reconfiguration of cortical networks during thepreparation of the forthcoming action. Functional connectivity patterns supported these findings, suggesting a critical role of frequency-specific inter-areal interactions in implementing top-down mechanisms in the sensorimotor system prior to action. These findings reveal that BP time-course reflects quantitative and qualitative changes in SMA communication patterns that shape mechanisms involved in motor readiness.

The Attentional Capture Debate: When Can We Avoid Salient Distractors and When Not?

There has been a long-standing debate concerning whether we are able to resist attention capture by salient distractors. The so-called "signal suppression hypothesis" of Gaspelin and Luck (2018) claimed to have resolved this debate. According to this view, salient stimuli "naturally attempt to capture attention", yet attention capture may be prevented by a top-down inhibitory mechanism. The current paper describes the conditions in which attention capture by salient distractors can be avoided. Capture by salient items can be avoided when the target is non-salient and therefore difficult to find. Because fine discrimination is needed, a small attentional window is adapted resulting in serial (or partly serial) search. Salient signals outside the focused attentional window do not capture attention anymore not because they are suppressed but because they are ignored. We argue that in studies that have provided evidence for signal suppression, search was likely serial or at least partly serial. When the target is salient, search will be conducted in parallel, and in those cases the salient singleton cannot be ignored nor suppressed but instead will capture attention. We argue that the "signal suppression" account (Gaspelin & Luck, 2018) that seeks to explain resistance to attentional capture has many parallels to classic visual search models such as the "feature integration theory" (Treisman & Gelade, 1980), "feature inhibition" account (Treisman & Sato, 1990), and "guided search" (Wolfe et al, 1989); all models that explain how the serial deployment of attention is guided by the output of earlier parallel processes.

Transcranial direct current stimulation over left dorsolateral prefrontal cortex facilitates auditory-motor integration for vocal pitch regulation.

A growing body of literature has implicated the left dorsolateral prefrontal cortex (DLPFC) in the online monitoring of vocal production through auditory feedback. Specifically, disruption of or damage to the left DLPFC leads to exaggerated compensatory vocal responses to altered auditory feedback. It is conceivable that enhancing the cortical excitability of the left DLPFC may produce inhibitory influences on vocal feedback control by reducing vocal compensations. We used anodal transcranial direct current stimulation (a-tDCS) to modulate cortical excitability of the left DLPFC and examined its effects on auditory-motor integration for vocal pitch regulation. Seventeen healthy young adults vocalized vowel sounds while hearing their voice pseudo-randomly pitch-shifted by ±50 or ±200 cents, either during (online) or after (offline) receiving active or sham a-tDCS over the left DLPFC. Active a-tDCS over the left DLPFC led to significantly smaller peak magnitudes and shorter peak times of vocal compensations for pitch perturbations than sham stimulation. In addition, this effect was consistent regardless of the timing of a-tDCS (online or offline stimulation) and the size and direction of the pitch perturbation. These findings provide the first causal evidence that a-tDCS over the left DLPFC can facilitate auditory-motor integration for compensatory adjustment to errors in vocal output. Reduced and accelerated vocal compensations caused by a-tDCS over left DLPFC support the hypothesis of a top-down neural mechanism that exerts inhibitory control over vocal motor behavior through auditory feedback.

Three potential neurovascular pathways driving the benefits of mindfulness meditation for older adults.

Mindfulness meditation has been shown to be beneficial for a range of different health conditions, impacts brain function and structure relatively quickly, and has shown promise with aging samples. Functional magnetic resonance imaging metrics provide insight into neurovascular health which plays a key role in both normal and pathological aging processes. Experimental mindfulness meditation studies that included functional magnetic resonance metrics as an outcome measure may point to potential neurovascular mechanisms of action relevant for aging adults that have not yet been previously examined. We first review the resting-state magnetic resonance studies conducted in exclusively older adult age samples. Findings from older adult-only samples are then used to frame the findings of task magnetic resonance imaging studies conducted in both clinical and healthy adult samples. Based on the resting-state studies in older adults and the task magnetic resonance studies in adult samples, we propose three potential mechanisms by which mindfulness meditation may offer a neurovascular therapeutic benefit for older adults: (1) a direct neurovascular mechanism via increased resting-state cerebral blood flow; (2) an indirect anti-neuroinflammatory mechanism via increased functional connectivity within the default mode network, and (3) a top-down control mechanism that likely reflects both a direct and an indirect neurovascular pathway.

Olfactory brain activations in patients with Major Depressive Disorder

Depression is associated with reduced olfactory function. This relationship is assumed to be based on either a reduced olfactory bulb volume or diminished functioning of higher cortical areas. As previous results are controversial, we aimed to re-evaluate central olfactory processing in depression. We recorded the BOLD signal of 21 patients with Major Depressive Disorder and 21 age and gender matched healthy controls during odor presentation. In addition, we measured the individual olfactory bulb volume, tested odor identification and odor threshold, and asked for hedonic odor perception. In both groups, odor presentation led to a pronounced activation of primary olfactory areas. However, secondary olfactory areas were significantly less activated in depressed individuals. The two groups did not differ in olfactory bulb volume. Our results point towards altered olfactory processing in patients in those regions that relate to sensory integration and attention allocation. Difficulties in cognitive processing could impact olfactory function in depression. We are therefore in favor of a top-down mechanism originating in higher cortical areas explaining parts of the relation between depression and olfaction.