Endogenous selective attention, the cognitive process of selectively attending to non-literal, ambiguous, or multistable interpretations of sensory input, remains poorly understood at the network level. To address this gap, we applied Granger causality (GC) analysis to electroencephalographic (EEG) recordings to characterize effective connectivity during sustained attention to ambiguous visual stimuli. Participants viewed the Necker cube, whose left and right faces were modulated at 6.67 Hz and 8.57 Hz, respectively, enabling objective tracking of perceptual dominance via steady-state visually evoked potentials (SSVEPs). GC analysis revealed robust directed connectivity between frontal and occipito-parietal areas during sustained perception of a specific cube orientation. We found that the magnitude of the GC-derived F-statistics correlated positively with attention performance indices during the left-face orientation task and negatively during the right-face orientation task, indicating that interregional causal influence scales with cognitive engagement in ambiguous interpretation. These results establish GC as a sensitive and reliable approach for characterizing dynamic, directional neural interactions during perceptual ambiguity, and, most notably, reveal, for the first time, an occipito-frontal effective connectivity architecture specifically recruited in support of endogenous selective attention. The methodology and findings hold translational potential for applications in neuroadaptive interfaces, cognitive diagnostics, and the study of disorders involving impaired symbolic processing.

Neuronal heterogeneity, characterized by a multitude of spiking neuronal patterns, is a widespread phenomenon throughout the nervous system. In particular, the brain exhibits strong variability among inhibitory neurons. Despite the huge neuronal heterogeneity across brain regions, which in principle could decrease synchronization due to differences in intrinsic neuronal properties, cortical areas coherently oscillate during various cognitive tasks. Therefore, the functional significance of neuronal heterogeneity remains a subject of active investigation. Previous studies typically focus on the role of heterogeneity in the dynamic properties of only one population. Here, we explore how different types of inhibitory neurons can contribute to the diversity of the phase relations between two cortical areas. This research sheds light on the potential impact of local properties, such as neuronal variability, on communication between distant brain regions. We show that both homogeneous and heterogeneous inhibitory networks can exhibit phase diversity and nonintuitive regimes such as anticipated synchronization (AS) and phase bistability. It has been proposed that the bistable phase could be related to bistable perception, such as in the Necker cube, where the brain alternates between two interpretations of a static image. Moreover, we show that heterogeneity enlarges the region of zero-lag synchronization and bistability. We also demonstrate that the parameter controlling inhibitory heterogeneity modulates the transition from the usual delayed synchronization regime (DS) to AS. Finally, we show that inhibitory heterogeneity drives the internal dynamics of the free-running population. Therefore, we suggest a possible mechanism to explain when the DS-AS transition occurs via zero-lag synchronization or bistability.

Greenways play a crucial role in enhancing citizens' quality of life by providing restorative environments, particularly in settings such urban forests. While existing research underscores the superior restorative qualities of natural settings compared to urban environments, our understanding of how various urban forest greenways and seasonal variations shape restorative experiences remains limited. This study investigates the restoration effects of various greenway scenes within the urban forests, including one urban greenway, one wilderness greenway and one tended greenway. A total of 55 university students viewed six videotaped greenway scenes in a randomized order. The urban and wilderness greenways were presented only for the summer scenes, while the tended greenway was shown across all four seasons. Physiological responses were measured using Electroencephalography (EEG), while psychological responses, including attentional levels and restorative experiences, were assessed with the Necker Cube and the Perceived Restorativeness Scale (PRS) respectively. This study confirmed previous research that the natural environment restored attention, and watching a combination of different types of greenways and seasons increased attentional level. Findings suggest that tended greenways offer more effective restoration compared to urban greenways. Notably, tended greenways in spring, summer, and autumn were more restorative than winter scenes. These findings highlight how different types of greenways and seasonal variations can affect perceived restorativeness. They provide valuable insights for the planning and management of urban forest greenways, emphasizing the importance of considering route selection, planting design, and maintenance to enhance restorative benefits.

Bistable figures can generate two different percepts alternating with each other. It is suggested that eye fixation plays an important role in bistable figure perception because it helps us selectively focus on certain image features. We tested how the shift of percept is related to the eye-fixation pattern and whether inhibition of return (IOR) plays a role in this process. IOR refers to the phenomenon where, after attention remains at the same image location for a period, the inhibition to the mechanisms supporting that location increases. Consequently, visual attention shifts to a new location, and reallocation to the original location is suppressed. We used an eye tracker to record the observers' eye movements during observation of the duck/rabbit figure and the Necker cube while recording their percept reversals. In Experiment 1, we showed there were indeed different eye fixation patterns for different percepts. Also, the fixation shifted across different regions that occurred before the percept reversal. In Experiment 2, we examined the influence of inward bias on the duck/rabbit figure and found that it had a significant effect on the first percept but that this effect diminished over time. In Experiment 3, a mask was added to the attended region to remove the local saliency. This manipulation increased the number of percept reversals and fixation shifts across different regions. That is, the change in local saliency can cause a fixation shift and thus reverse our perception. Our result shows that what we perceive depends on where we look.

Hypergraph analysis extends traditional graph theory by enabling the study of complex, many-to-many relationships in networks, offering powerful tools for understanding brain connectivity. This case study introduces a novel methodology for constructing both graphs and hypergraphs of functional brain connectivity during figurative attention tasks, where subjects interpret the ambiguous Necker cube illusion. Using a frequency-tagging approach, we simultaneously modulated two cube faces at distinct frequencies while recording electroencephalography (EEG) responses. Brain connectivity networks were constructed using multiple measures—coherence, cross-correlation, and mutual information—providing complementary insights into functional relationships between regions. Our hypergraph analysis revealed distinct connectivity patterns associated with attending to different cube orientations, including previously unobserved higher-order relationships between brain regions. The results demonstrate bilateral cortico–cortical interactions and suggest integrated processing hubs that may coordinate visual attention networks. This methodological framework not only advances our understanding of the neural basis of visual attention but also offers potential applications in attention monitoring and clinical assessment of attention disorders. While based on a single subject, this proof-of-concept study establishes a foundation for larger-scale investigations of brain network dynamics during ambiguous visual processing.

The occurrence of spontaneous switches between different interpretations of unchanging, ambiguous stimuli reflects the dynamic nature of unconscious perceptual processing. These perceptual alternations are explained by reciprocal inhibition, where one perception is suppressed while another emerges. The temporal patterns of these shifts vary between people but remain consistent within individuals, potentially reflecting underlying neural and psychological factors. Cognitive flexibility, the ability to switch tasks by inhibiting irrelevant information, may be related to perceptual flexibility. The present study (n = 48) explored the relationship between perceptual dynamics in the Necker Cube and higher-order cognitive processes. Switching rates and perspective durations were correlated with performance on computerized tasks (Stroop Test, Simon Task, and Task Switching Tests) and self-reported scales (Cognitive Flexibility Test, Barratt's Impulsiveness Scale, Depression, Anxiety, and Stress Scale, and Big Five Personality Traits Questionnaire). Results revealed correlations between perceptual dynamics, reaction times, and Cognitive Impulsiveness, suggesting links between perceptual alternation, cognitive processes, and personality traits. Future research should investigate the common mechanisms underlying these processes and investigate causality and temporal dynamics.

During visual imagination, a perceptual representation is activated in the absence of sensory input. This is sometimes described as seeing with the mind's eye. A number of physiological studies indicate that the brain uses more or less the same neural resources for visual perception of sensory information and visual imagination. The intensity of visual imagination is typically assessed with questionnaires, while more objective measures are missing. Aim of the present study was, to test a new experimental paradigm that may allow to objectively quantify imagination. For this, we used priming and adaptation effects during observation of ambiguous figures. Our perception of an ambiguous stimulus is unstable and alternates spontaneously between two possible interpretations. If we first observe an unambiguous stimulus variant (the conditioning stimulus), the subsequently presented ambiguous stimulus can either be perceived in the same way as the test stimulus (priming effect) or in the opposite way (adaptation effect) as a function of the conditioning time. We tested for these conditioning effects (priming and adaptation) using an ambiguous Necker Cube and an ambiguous Letter /Number stimulus as test stimuli and unambiguous variants thereof as conditioning stimuli. In a second experimental condition, we tested whether the previous imagination of an unambiguous conditioning stimulus variant - instead of its observation - can have similar conditioning effects on the subsequent test stimulus. We found no systematic conditioning effect on the group level, neither for the two stimulus types (Necker Cube stimuli and Letter /Number stimuli) nor for the two conditions (Real and Imaginary). However, significant correlations between effects of Real and Imaginary Condition were observed for both stimulus types. The absence of conditioning effects at the group level may be explained by using only one conditioning time, which may fit with individual priming and adaptation constants of some of our participants but not of others. Our strong correlation results indicate that observers with clear conditioning effects have about the same type (priming or adaptation) and intensity of imaginary conditioning effects. As a consequence, not only past perceptual experiences but also past imaginations can influence our current percepts. This is further confirmation that the mechanisms underlying perception and imagination are similar. Our post-hoc qualitative observations from three self-defined aphantasic observers indicate that our paradigm may be a promising objective measure to identify aphantasia.

The discovery of the quantum tunneling (QT) effect—the transmission of particles through a high potential barrier—was one of the most impressive achievements of quantum mechanics made in the 1920s. Responding to the contemporary challenges, I introduce a deep neural network (DNN) architecture that processes information using the effect of QT. I demonstrate the ability of QT-DNN to recognize optical illusions like a human. Tasking QT-DNN to simulate human perception of the Necker cube and Rubin’s vase, I provide arguments in favor of the superiority of QT-based activation functions over the activation functions optimized for modern applications in machine vision, also showing that, at the fundamental level, QT-DNN is closely related to biology-inspired DNNs and models based on the principles of quantum information processing.

The early decades of the twenty-first century have witnessed various attempts by cultural critics to move beyond the Two Cultures divide posited by C.P. Snow in 1959 , developing modes of critique that seek to bridge the gap between humans and the technology we use. This has resulted in relational interpretations of literature and technology that emphasise the interpenetrative nature of the reading experience, and the complex implications of conceiving of literature and technology as a system. Amazon's Kindle™ ebook reader provides an exceptional use case to ground this conversation, occupying a position somewhere between traditional reading device and techno-corporate publishing mechanism. Analyses of the Kindle™ often fail to take into account useful twentieth-century approaches to the philosophy of technology that offer purchase over the problem domain, however. Work by John Dewey (1859–1952) and Donald Ihde (1934–2024) suggest ways to conceive of the Kindle™ and similar devices as objects embedded in our experience of the world, mediated by technological systems and infrastructure but ultimately contributing to our experience of the world in much the same way as previous modes of publishing.

Ambiguous optical illusions have been a paradigmatic object of fascination, research and inspiration in arts, psychology and video games. However, accurate computational models of perception of ambiguous figures have been elusive. In this paper, we design and train a deep neural network model to simulate human perception of the Necker cube, an ambiguous drawing with several alternating possible interpretations. Defining the weights of the neural network connection using a quantum generator of truly random numbers, in agreement with the emerging concepts of quantum artificial intelligence and quantum cognition, we reveal that the actual perceptual state of the Necker cube is a qubit-like superposition of the two fundamental perceptual states predicted by classical theories. Our results finds applications in video games and virtual reality systems employed for training of astronauts and operators of unmanned aerial vehicles. They are also useful for researchers working in the fields of machine learning and vision, psychology of perception and quantum–mechanical models of human mind and decision making.

In his main works, René Descartes, in addition to such an impressive metaphysical construction, over and over again gives promises of happiness, which must certainly accompany the study of philosophy according to a new model. What exactly is this happiness and is the Cartesian construction capable of fulfilling this promise? For whom can it come? If we take this promise seriously as instructions for obtaining vita beata, then the character of the Cartesian story about the construction of a new science has a serious competitor, the main character of Victor Pelevin’s novel KGBT+, who performs the same procedures as the Cartesian one, and the matches are exact, and the key act is the walk, ambulo-sum(nt): both Descartes (and his followers, Gottfried Wilhelm Leibniz and Benedictus de Spi- noza) and Pelevin show one thing: a walk is not a reward for a job well done to salvation, it is work itself. This is blissful work, in which the path and the goal coincide, just like in a walk, when we walk just for walking. And Pelevin promises happiness, but it does not happen to the Cartesian subject at all. Thanks to the third figure, Giordano Bruno, this confrontation is proposed to be viewed not as a contradiction, but in such a way that the promise can be fulfilled only by abandoning the concept of extension in favor of space. After all, when walking, it’s more important not who is walking, but where, there are places and spaces in which you won’t be able to walk. The Necker Cube helps us understand the concept of the space in which the three described walks (Descartes’, Pelevin’s and Bruno’s) take place, aimed at finding the highest goal of the teachings, of which these characters are adherents.

Bistable perception follows from observing a static, ambiguous, (visual) stimulus with two possible interpretations. Here, we present an active (Bayesian) inference account of bistable perception and posit that perceptual transitions between different interpretations (i.e. inferences) of the same stimulus ensue from specific eye movements that shift the focus to a different visual feature. Formally, these inferences are a consequence of precision control that determines how confident beliefs are and change the frequency with which one can perceive-and alternate between-two distinct percepts. We hypothesized that there are multiple, but distinct, ways in which precision modulation can interact to give rise to a similar frequency of bistable perception. We validated this using numerical simulations of the Necker cube paradigm and demonstrate the multiple routes that underwrite the frequency of perceptual alternation. Our results provide an (enactive) computational account of the intricate precision balance underwriting bistable perception. Importantly, these precision parameters can be considered the computational homologs of particular neurotransmitters-i.e. acetylcholine, noradrenaline, dopamine-that have been previously implicated in controlling bistable perception, providing a computational link between the neurochemistry and perception.

Objective:Visuospatial skills are frequently assessed with drawing tests. Research has suggested that the use of drawing tasks in low educated groups may lack the ability to discriminate healthy individuals from clinical populations. The aims of this study were to investigate the validity of visuoconstructional tests in a sample of older Greek Australian immigrants and compare their performances to a matched sample of patients with Alzheimer’s disease (AD).Participants and Methods:We assessed visuoconstructional performances in a sample of 90 healthy older Greek Australians, with a primary school level of education, and compared performances to a demographically matched sample of 20 Greek Australians with a diagnosis of AD on four visuoconstructional drawing tests: Greek cross, four-pointed star, intersecting pentagons, and the Necker Cube.Results:While healthy participants tended to outperform the AD group on most copy tasks, high fail rates within the healthy sample were observed for the intersecting pentagons and Necker cube (78% and 73% fail rates respectively) when using established clinical cutoff scores. High rates of curved angle, omission, distorted relation between elements, spatial disorganization and three-dimensional design errors were found across the four-pointed star, intersecting pentagons, and the Necker cube in both healthy participants and those with AD. Exploratory receiver operating characteristic curve analysis revealed that, with perhaps the exception of the Greek cross, meaningful sensitivity and specificity could not be reached for the four-pointed star, intersecting pentagons, and Necker cube.Conclusions:Cognitively healthy immigrants with low education appear to be at a disadvantage when completing visuoconstructional drawing tests, as their performance may be misinterpreted as indicating cognitive impairment. Future research is needed to identify alternative approaches to assess visuoconstructional ability in low education older cohorts.

When viewing a completely ambiguous image, different interpretations can switch involuntarily due to internal top-down processing. In the case of the Necker cube, an entirely ambiguous stimulus, observers often display a bias in perceptual switching between two interpretations based on their perspectives: one with a from-above perspective (FA) and the other with a from-below perspective (FB). Typically, observers exhibit a priori top-down bias in favor of the FA interpretation, which may stem from a statistical tendency in everyday life where we more frequently observe objects from above. However, it remains unclear whether this perceptual bias persists when individuals voluntarily decide on the Necker cube's interpretation in goal-directed behavior, and the impact of ambiguity in this context is not well-understood. In our study, we instructed observers to voluntarily identify the orientation of a Necker cube while manipulating its ambiguity from low (LA) to high (HA). Our investigation aimed to test two hypotheses: (i) whether the perspective (FA or FB) would result in a bias in response time, and (ii) whether this bias would depend on the level of stimulus ambiguity. Additionally, we analyzed electroencephalogram (EEG) signals to identify potential biomarkers that could explain the observed perceptual bias. The behavioral results confirmed a perceptual bias in favor of the from-above perspective, as indicated by shorter response times. However, this bias diminished for stimuli with high ambiguity. For the LA stimuli, the occipital theta-band power consistently exceeded the frontal theta-band power throughout most of the decision-making time. In contrast, for the HA stimuli, the frontal theta-band power started to exceed the occipital theta-band power during the 0.3-s period preceding the decision. We propose that occipital theta-band power reflects evidence accumulation, while frontal theta-band power reflects its evaluation and decision-making processes. For the FB perspective, occipital theta-band power exhibited higher values and dominated over a longer duration, leading to an overall increase in response time. These results suggest that more information and more time are needed to encode stimuli with a FB perspective, as this template is less common for the observers compared to the template for a cube with a FA perspective.

Changing a problem’s representation is a crucial process when solving insight problems. Recently, Laukkonen and Tangen (2017) found that observing ambiguous figures such as a Necker Cube before solving problems can increase insight frequency. In our research, we extended their procedure by including measures of feelings of insight (e.g., confidence and pleasure). This approach allowed us to test the replicability of relationships between perceptual switching and insight frequency in terms of both accuracy of problem solutions and insight phenomenology. The research took the form of two studies using two different samples (NA = 68 and NB = 198) using online platforms. Our results consistently showed no effect of prior Necker cube perception on accuracy. However, we found a significant difference in self- reported insight (1 - non-aha! experience to 5 – a very strong aha! experience) in our Sample B study. The results suggest the possibility that viewing ambiguous figures may not have a triggering effect on insight problem-solving performance but that it may trigger stronger insight experiences when solving insight problems.

Perceptual multistability is well-known and mostly visually demonstrated: Common examples are Necker's cube or Rubin's face-vase that produce qualitatively different percepts continuously oscillating between the solutions despite physically stable stimuli. We lack knowledge about similar phenomena in other domains, for instance in linguistics, where we are faced with homonyms that create multistability of cognitive semantics, differently assigned meanings of identical words. Our participants listened to repeated presentations of homonyms for which two or even three meanings could be assigned, and they reported the dominant meaning perceived at a certain point in time. Results showed that most participants experienced multistability of meaning for homonyms, with semiperiodic changes in dominant meaning similar to multistabity in perception. These findings suggest that multistability is a general property of the brain's neural architecture that resolves ambiguity irrespective of the level of representation.

IntroductionDuring observation of the ambiguous Necker cube, our perception suddenly reverses between two about equally possible 3D interpretations. During passive observation, perceptual reversals seem to be sudden and spontaneous. A number of theoretical approaches postulate destabilization of neural representations as a pre-condition for reversals of ambiguous figures. In the current study, we focused on possible Electroencephalogram (EEG) correlates of perceptual destabilization, that may allow prediction of an upcoming perceptual reversal.MethodsWe presented ambiguous Necker cube stimuli in an onset-paradigm and investigated the neural processes underlying endogenous reversals as compared to perceptual stability across two consecutive stimulus presentations. In a separate experimental condition, disambiguated cube variants were alternated randomly, to exogenously induce perceptual reversals. We compared the EEG immediately before and during endogenous Necker cube reversals with corresponding time windows during exogenously induced perceptual reversals of disambiguated cube variants.ResultsFor the ambiguous Necker cube stimuli, we found the earliest differences in the EEG between reversal trials and stability trials already 1 s before a reversal occurred, at bilateral parietal electrodes. The traces remained similar until approximately 1100 ms before a perceived reversal, became maximally different at around 890 ms (p = 7.59 × 10–6, Cohen’s d = 1.35) and remained different until shortly before offset of the stimulus preceding the reversal. No such patterns were found in the case of disambiguated cube variants.DiscussionThe identified EEG effects may reflect destabilized states of neural representations, related to destabilized perceptual states preceding a perceptual reversal. They further indicate that spontaneous Necker cube reversals are most probably not as spontaneous as generally thought. Rather, the destabilization may occur over a longer time scale, at least 1 s before a reversal event, despite the reversal event as such being perceived as spontaneous by the viewer.

After briefly reviewing the appealing psychological properties of PDP systems, an introduction to their historical roots and basic computational mechanisms are provided. A variety of network architectures are described including one-layered perceptrons, backpropagation networks, Boltzmann machines and recurrent systems. Three PDP simulations are analysed: First, a model that purports to learn the past tense of English verbs; Second, a constraint satisfaction network which is able to interpret the alternative configurations of a Necker cube; Finally, a recurrent network which is able to decipher membership of grammatical classes from word-order information. The notion that PDP approaches provide a sub-symbolic account of cognitive processes, in contrast to theclassical symbolic view, is examined. The article concludes with brief speculation concerning the explanatory power of PDP systems at the cognitive level of functioning.

Abstract The study of cases of illusory or unstable perception of some visual stimuli allows exploration of the psychology of perception of the surrounding world. The wired construction known as “Necker cube” is one such stimulus: it can be perceived as a cube whose front face is seen higher than the back face or vice versa. The switch can occur intentionally or spontaneously. The investigations were focused on switching parameters, relation of the switching to eye position, pre-history, and environment. Here we define that the kernel of the problem is recognizing the 2D drawing as a 3D Necker cube. To this end, we have expanded Gestalt's psychology methods that allow us to recognize 2D figures in drawings for recognizing 3D figure in a flat drawing (including the Necker cube). The presented algorithm for recognizing the cube based on the imitation principle allowed the development of the model of switching between two possible perceptions of the Necker cube. The paper shows that the predictions are in conformity with previously available experimental data. The results confirm the imitation principle of perception, and suggest expanding our research on perception to a wider class of 3D figures, opening a window into the internal processes of perception.

Observers can voluntarily avoid reversals of an ambiguous, reversible figure, extending the duration of an intended percept. This is usually attributed to high-level, top-down attentional processes. However, voluntary control is limited. Reversals occur despite attempts to avoid them. In two experiments, observers demonstrated significant, but limited, voluntary control over Necker cube perception. Cube size and cube completeness, variables associated with stimulus-driven processes involving neural adaptation, influenced the frequency of reversals regardless of observers' intentions. Results are consistent with the hybrid hypothesis that both top-down and bottom-up processes contribute to Necker-cube perception and support the hypothesis that the contribution of bottom-up processes is responsible for the limitation on voluntary control.