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Multistable perception
Multistable perception
Multistable perception
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Examples of visually ambiguous patterns. From top to bottom: Necker cube, Schroeder stairs and a figure that can be interpreted as black or white arrows.

Multistable perception (or bistable perception) is a perceptual phenomenon in which an observer experiences an unpredictable sequence of spontaneous subjective changes. While usually associated with visual perception (a form of optical illusion), multistable perception can also be experienced with auditory and olfactory percepts.

Classification

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Perceptual multistability can be evoked by visual patterns that are too ambiguous for the human visual system to definitively and uniquely interpret. Familiar examples include the Necker cube, Schroeder staircase, structure from motion, monocular rivalry, and binocular rivalry, but many more visually ambiguous patterns are known. Because most of these images lead to an alternation between two mutually exclusive perceptual states, they are sometimes also referred to as bistable perception.[1]

Auditory and olfactory examples can occur when there are conflicting, and so rival, inputs into the two ears[2] or two nostrils.[3]

Characterization

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The transition from one precept (an undefined term) to its alternative (the defined term) is called a perceptual reversal (Paradigm shift). They are spontaneous and stochastic events that cannot be eliminated by intentional efforts, although some control over the alternation process is learnable. Reversal rates vary drastically between stimuli and observers. They are slower for people with bipolar disorder.[4][5]

Cultural history

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Human interest in these phenomena can be traced back to antiquity.[citation needed] The fascination with multistable perception probably comes from the active nature of endogenous perceptual changes or from the dissociation of dynamic perception from constant sensory stimulation.

Multistable perception was a common feature in the artwork of the Dutch lithographer M. C. Escher, who was strongly influenced by mathematical physicists such as Roger Penrose.[citation needed]

Examples

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Real-world phenomena

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Photographs of craters, from either the moon or other planets including our own, can exhibit this phenomenon. Craters in stereo vision, such as our eyes, normally appear concave. However, in monocular presentations, such as photographs, the elimination of our depth perception causes multistable perception, which can cause the craters to look like plateaus rather than pits. For humans, the "default" interpretation comes from an assumption of top-left lighting, so that rotating the image by 180 degrees can cause the perception to suddenly switch.[6][7] This phenomenon is called the concave/convex, or simply up/down, ambiguity, and it confuses computer vision as well.[8]

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In literature, the science fiction novel Dhalgren by Samuel R. Delany, contains circular text, multistable perception, and multiple entry points.[citation needed]

Multistable perception arises with the theater segments of Mystery Science Theater 3000, as due to the construction of the Crow T. Robot puppet, its head can appear to be facing towards the camera rather than towards the film being shown. This was addressed by the creators of the series, even likening Crow to a Necker cube[9] or The Spinning Dancer.[when?]

See also

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Bibliography

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Sources

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  1. ^ Eagleman, D. (2001). "Visual Illusions and Neurobiology" (PDF). Nature Reviews Neuroscience. 2 (12): 920–926. doi:10.1038/35104092. PMID 11733799. S2CID 205023280. Archived from the original (PDF) on 2007-09-27.
  2. ^ Deutsch, D. (1974). "An Auditory Illusion". Nature. 251 (5473): 307–309. doi:10.1038/251307a0. PMID 4427654. S2CID 4273134.
  3. ^ Zhou, W.; Chen, D. (2009). "Binaral Rivalry Between the Nostrils and in the Cortex". Current Biology. 19 (18): 1561–1565. doi:10.1016/j.cub.2009.07.052. PMC 2901510. PMID 19699095.
  4. ^ Pettigrew, J. D.; Miller, S. M. (1998). "A 'sticky' interhemispheric switch in bipolar disorder?". Proceedings of the Royal Society B: Biological Sciences. 265 (1411): 2141–2148. doi:10.1098/rspb.1998.0551. PMC 1689515. PMID 9872002.
  5. ^ Miller, S. M.; Gynther, B. D.; Heslop, K. R.; Liu G. B.; Mitchell, P. B.; Ngo, T. T.; Pettigrew, J. D.; Geffen, L. B. (2003). "Slow Binocular Rivalry in Bipolar Disorder" (PDF). Psychological Medicine. 33 (4): 683–692. CiteSeerX 10.1.1.693.9166. doi:10.1017/S0033291703007475. PMID 12785470. S2CID 30727987. Archived from the original (PDF) on 2018-10-03. Retrieved 2006-09-24.
  6. ^ "A lunar illusion you'll flip over". Discover Magazine.
  7. ^ Minutephysics (29 June 2017). "The "Mountain Or Valley?" Illusion". YouTube. Archived from the original on 2021-12-12.
  8. ^ Breuß, Michael; Mansouri, Ashkan; Cunningham, Douglas (2018). "The Convex-Concave Ambiguity in Perspective Shape from Shading". Proceedings of the OAGM Workshop 2018. doi:10.3217/978-3-85125-603-1-13. ISBN 978-3-85125-603-1.
  9. ^ Trace Beaulieu ... (1996). The Mystery Science Theater 3000 Amazing Colossal Episode Guide. Bantam. p. 159. ISBN 978-0-553-37783-5.
[edit]
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Multistable perception

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Multistable perception is a phenomenon in which a single, unchanging sensory stimulus—most commonly visual—gives rise to alternating, mutually exclusive perceptual interpretations in the observer, with spontaneous switches occurring every few seconds without external cues. This process highlights the brain's active role in constructing from ambiguous inputs, rather than passively reflecting sensory data. Classic examples of multistable perception include the Necker cube, a line drawing of a cube that flips between two depth interpretations; Rubin's vase, an image alternating between a vase and two facing profiles; bistable apparent motion, where dots seem to move in competing directions; and binocular rivalry, where conflicting images presented to each eye compete for dominance. These demonstrations, first systematically studied in vision over a century ago, extend to other senses like audition and touch, though visual cases predominate in research. At the neural level, multistable perception involves interactions across brain regions: early visual areas like V1 show limited direct involvement in driving switches, while extrastriate cortex activity strongly correlates with the dominant percept, and higher areas such as parietal and prefrontal cortex play a causal role in initiating reversals. This dissociation between stable sensory input and fluctuating awareness makes multistable perception a key model for investigating the neural correlates of consciousness, revealing how top-down processes resolve perceptual ambiguity and balance stability against sensitivity to change. Research, including functional imaging and neurostimulation studies, underscores its relevance to understanding disorders like schizophrenia, where perceptual stability may be disrupted.

Core Concepts

Definition and Characteristics

Multistable perception refers to the spontaneous and endogenous alternations in an observer's perceptual experience arising from a single, ambiguous sensory stimulus that admits multiple stable and mutually exclusive interpretations. These alternations occur without any change in the physical properties of the stimulus, reflecting the brain's active construction of perception rather than passive reflection of sensory input. Typically, the phenomenon manifests as (two interpretations) or multistability (more than two), where the percept flips unpredictably between valid alternatives. Key characteristics include the subjective and involuntary nature of these perceptual shifts, which are experienced as vivid and immersive despite the static stimulus. Switching rates are generally unpredictable but follow a unimodal, asymmetric distribution, with typical dominance durations per phase ranging from 1 to 10 seconds across common visual paradigms. These rates exhibit inter-individual variability and can be modulated by factors such as , which may stabilize a given percept or accelerate transitions, and levels, which influence the overall pace of alternations. Unlike deterministic , the process is , with only one interpretation dominating at a time, suppressing rivals. Multistable perception differs fundamentally from perceptual illusions, which involve distortions or misinterpretations of unambiguous stimuli leading to a single, erroneous percept rather than rivalry between equally valid alternatives. In multistability, the competing percepts are both perceptually lawful and consistent with the sensory data, engaging competitive neural processes without inherent error. Classic illustrative examples include the , where a wireframe cube ambiguously reverses in perceived depth, and Rubin's , which alternates between a vase silhouette and two facing profiles as figure and ground.

Classification

Multistable perception is primarily classified by sensory modality, encompassing visual, auditory, olfactory, and cross-modal phenomena, each involving stimuli that yield alternating perceptual interpretations. Visual multistability, the most extensively studied category, includes figure-ground , where ambiguous boundaries alternate between foreground and background dominance, and structure-from-motion, where rotating dots are perceived as rotating in depth in opposing directions. Auditory multistability arises from dichotic presentations, such as dichotic pitch stimuli where conflicting tones to each ear alternate in perceptual salience. Olfactory multistability, less common but documented, manifests as nostril or binaral , in which dissimilar odors presented to each lead to sequential dominance of one scent over the other. Cross-modal multistability involves interactions between modalities, such as audio-visual integration failures where conflicting auditory and visual cues, like mismatched and lip movements, result in alternating perceptual bindings. Within these modalities, phenomena are further subdivided into bistable and multistable subtypes based on the number of competing interpretations, as well as ambiguous versus rivalrous stimuli. Bistable perception involves exactly two mutually exclusive percepts, such as the alternating orientations in binocular rivalry, while multistable perception accommodates three or more, as in the multiple depth interpretations of a rotating hollow mask. Ambiguous stimuli, often , permit simultaneous but unstable interpretations resolved by perceptual switching, whereas rivalrous stimuli, typically dichoptic or inter-modal, enforce perceptual exclusivity through mutual suppression, preventing co-occurrence of interpretations. Classification criteria emphasize stimulus ambiguity level, rivalry mechanisms, and perceptual exclusivity. Ambiguity level refers to the degree of interpretational uncertainty in the input, ranging from high in inherently vague patterns to moderate in conflicting signals across channels. Rivalry mechanisms include interocular suppression in visual , where input from one eye dominates while suppressing the other, or analogous inter-nostril suppression in olfactory cases. Perceptual exclusivity ensures that only one interpretation prevails at a time, a hallmark distinguishing multistability from stable multimodal integration. These criteria are often associated with observed switching rates of approximately 10-30 per minute in visual cases. Evolutionary and comparative perspectives highlight the prevalence of multistable perception in humans and non-human animals, suggesting conserved perceptual processes. For instance, monkeys exhibit binocular rivalry dynamics akin to humans, with perceptual alternations and neural correlates in early visual areas mirroring human patterns during ambiguous viewing. This cross-species similarity in visual rivalry indicates an adaptive role in resolving sensory ambiguity, though auditory and olfactory forms remain less explored in animals.

Underlying Mechanisms

Perceptual Dynamics

Multistable involves spontaneous perceptual reversals that exhibit a fundamentally nature, where the durations of dominance for each competing percept fluctuate irregularly over time. These dominance durations typically follow a , characterized by a that captures the and variability observed in empirical data. The reversal rate, denoted as λ\lambda, quantifies the of these switches and can be derived from the statistical properties of dominance periods as λ=1μ\lambda = \frac{1}{\mu}, where μ\mu represents the dominance duration, reflecting the stability of perceptual phases. Several behavioral factors modulate these reversal dynamics. Directing toward one percept can accelerate the onset of reversals, effectively shortening dominance durations by enhancing sensitivity to alternative interpretations. Prolonged practice with a multistable stimulus stabilizes perceptual phases, resulting in longer and more consistent dominance periods as observers become habituated to the ambiguity. Moreover, the process demonstrates history dependence, wherein a percept that has been briefly suppressed tends to exhibit extended dominance upon reemergence, suggesting a temporary bias favoring recovery from inhibition. To capture these temporal patterns, researchers rely on established measurement techniques that prioritize behavioral indicators. Verbal reports remain the primary method, with observers signaling switches via button presses or movements to log the timing and sequence of dominance changes. Eye-tracking complements this by monitoring fixation stability and subtle oculomotor shifts, such as microsaccades or alterations, which often correlate with perceptual transitions without requiring explicit reporting. Individual differences profoundly affect reversal dynamics, highlighting variability in perceptual processing. Older adults typically exhibit slower reversal rates, with reduced frequency of switches linked to age-related declines in . In clinical populations, such as those with , binocular rivalry displays notably reduced rates and lower variability, pointing to altered temporal organization in ambiguous .

Neural and Cognitive Basis

Multistable perception involves dynamic neural processes where ambiguous sensory inputs lead to alternating conscious experiences, with neural correlates identified across cortical hierarchies. In the early , particularly area V1, (fMRI) studies reveal that blood-oxygen-level-dependent (BOLD) signals alternate in strength corresponding to the dominant percept during binocular rivalry, indicating suppression of the non-dominant stimulus at low-level sensory stages. Higher cortical areas, such as the lateral intraparietal area (LIP) and frontal eye fields (FEF), contribute to attention-modulated perceptual switches, with fMRI evidence showing transient activations in these frontoparietal regions preceding spontaneous alternations. These findings underscore a distributed network where low-level adaptation interacts with high-level attentional control to resolve perceptual ambiguity. Cognitive factors exert top-down influence on multistability, modulating the stability and timing of perceptual states. The plays a causal role in initiating switches through inhibitory mechanisms, as demonstrated by disrupting alternations when targeting dorsolateral prefrontal regions. contributes to percept stabilization by maintaining representations of the current interpretation, with brief interruptions in stimulus presentation leading to prolonged dominance of the pre-interruption percept, reflecting a trace. further biases dominance durations, with voluntary shifts prolonging the attended percept's reign. Theoretical models frame multistability as an inferential process balancing sensory evidence and prior expectations. In the framework, higher-level predictions about the stimulus are continuously compared to bottom-up sensory inputs, with accumulating prediction errors from the suppressed percept triggering switches to restore perceptual consistency. dynamics, a core component, can be modeled by the dAdt=−kA+I,\frac{dA}{dt} = -kA + I, where AA represents the adaptation level of a neural population, II is the constant input strength, and kk is the decay rate, leading to gradual buildup that favors alternation after prolonged suppression. Pathological conditions reveal altered multistable dynamics linked to neural imbalances. In autism spectrum disorder, individuals exhibit slower perceptual switching rates, with studies on illusions showing significantly fewer reversals (median 1.8 per minute) compared to neurotypical controls (median 5 per minute), suggesting enhanced perceptual stability or reduced flexibility in top-down modulation. In depression, prolonged dominance periods and reduced alternation rates occur, indicative of biased , which can be partially reversed by treatments that normalize switch frequencies. These insights highlight how disruptions in frontoparietal and prefrontal networks impair the adaptive resolution of perceptual ambiguity.

Historical Development

Early Observations

The earliest observations of phenomena resembling multistable perception can be traced to , where described subjective visual experiences that shifted over time. In his work De Sensu et Sensibilibus (part of the Parva Naturalia), Aristotle documented illusions such as the , in which prolonged viewing of a moving object leads to the perception of opposite motion upon fixation, and afterimages, where a stared-at color appears complementary when the gaze shifts. These accounts highlight early recognition of how stable stimuli can evoke alternating perceptual states, laying groundwork for understanding perceptual instability. During the , interest in visual ambiguities grew through artistic and scientific inquiry into perspective. , in his notebooks, explored how linear perspective and optical effects could create deceptive depth and in paintings, noting that the eye could be "deceived" by arrangements of lines and shadows that suggested multiple spatial interpretations. For instance, da Vinci observed that certain configurations in art mimicked real scenes but allowed for perceptual reversals depending on viewpoint, influencing later studies of illusory space. Philosophical debates in further contextualized these observations by questioning the reliability of perception against objective . , in (1690), argued that sensory ideas form the basis of knowledge but can be erroneous due to the mind's interpretive role, suggesting perception as a fallible mediator between external objects and internal experience. extended this in A Treatise Concerning the Principles of Human Knowledge (1710), positing that existence depends on being perceived (esse est percipi), which implied that apparent contradictions in sensory input reveal the mind's constructive nature rather than true in . These empiricist views framed perceptual shifts as of subjective , influencing 19th-century scientific approaches. In the , empirical investigations advanced these ideas into formalized observations of multistability. Charles Wheatstone's invention of the in 1838 demonstrated binocular rivalry, where conflicting images presented to each eye alternate in dominance, producing spontaneous perceptual switches without stimulus change. built on this in his Handbuch der physiologischen Optik (1867), theorizing perceptual ambiguity as resulting from "unconscious inferences" where the brain resolves ambiguous sensory data through prior knowledge, often leading to alternating interpretations of the same input. Non-Western traditions also engaged with perceptual illusion philosophically. In ancient Indian philosophy, the concept of māyā—elaborated by Ādi Śaṅkara in the 8th century—described the perceived world as an illusory veil obscuring ultimate reality (), where sensory experiences mislead through apparent multiplicity and change. This notion parallels multistable perception by emphasizing how stable external forms yield deceptive, shifting apprehensions of truth.

Modern Advancements

In the early 20th century, Gestalt psychologists provided foundational analyses of multistable perception through their examination of ambiguous figures like the , originally described in 1832 but reinterpreted in the 1920s as evidence of perceptual organization principles such as figure-ground segregation and Prägnanz. Max Wertheimer's 1923 work highlighted how the cube's reversals demonstrated the brain's tendency to impose holistic structure on ambiguous stimuli, influencing subsequent theories of perceptual grouping. further advanced these ideas in the 1940s by integrating electrophysiological observations into Gestalt frameworks, proposing that multistability arises from dynamic neural field interactions rather than isolated sensory elements. Mid-20th-century developments built on Gestalt foundations by exploring rivalry mechanisms and early neurophysiological correlates. Gestalt psychology's emphasis on emergent properties informed rivalry theories, positing that perceptual alternations resolve competition between incompatible interpretations through global contextual integration, as elaborated in Köhler's 1940 synthesis of perceptual dynamics. In the , initial EEG studies revealed rhythmic correlates of multistable switches, such as alpha-band modulations during binocular rivalry, indicating cortical involvement in perceptual transitions beyond low-level . By the 1970s, empirical breakthroughs included Attneave's demonstrations of multistability in motion displays, where rotating patterns evoked alternating interpretations, underscoring the role of motion cues in perceptual ambiguity. This work highlighted how kinetic stimuli could sustain -like alternations, bridging static illusions with dynamic vision. In the 1990s, Logothetis pioneered primate studies on binocular , recording single-unit activity in visual cortex to show that neuronal responses in higher areas like IT and V4 correlate more closely with perceptual dominance than early V1 activity, challenging bottom-up models of . These findings established as a tool for probing conscious vision. Key figures shaped rivalry paradigms during this era: Köhler's Gestalt legacy influenced holistic theories; Randolph Blake refined binocular rivalry techniques in the late 20th century, developing adaptation models to localize suppression sites and demonstrating interocular grouping effects. Jan Brascamp extended these in the 2000s by quantifying noise-driven dynamics in rivalry time courses, revealing how stochastic fluctuations govern switch rates. Entering the early , neuroimaging integrations advanced the field, with fMRI studies in the identifying frontoparietal networks as key to rivalry resolution, showing increased BOLD signals in the and during perceptual switches. These activations suggested top-down modulation stabilizes multistable states. Concurrently, computational modeling proliferated, with frameworks by 2010 simulating rivalry as noisy transitions between stable neural states, where mutual inhibition and adaptation parameters predict alternation rates observed in human and primate data. Such models, often based on Wilson-Cowan equations, provided mechanistic explanations for empirical patterns without requiring precise anatomical details. In the and , Bayesian frameworks further integrated probabilistic into explanations of multistable dynamics, while optogenetic studies in animals confirmed causal roles of frontoparietal circuits in perceptual switches.

Examples and Phenomena

Visual Instances

Multistable perception manifests prominently in visual stimuli through ambiguous figures that elicit spontaneous alternations between competing interpretations. One of the earliest and most iconic examples is the , a wireframe line drawing of a transparent cube that alternates between two possible three-dimensional orientations: one where the lower-left face appears as the front (viewed from above) and another where the upper-right face appears as the front (viewed from below). First described by Swiss crystallographer Louis Albert Necker in 1832 while analyzing engravings of crystal lattices, the stimulus exploits the lack of explicit depth cues, allowing the to resolve the ambiguity by flipping between equally plausible 3D structures roughly every few seconds during prolonged viewing. Another classic figure-ground rivalry stimulus is Rubin's vase, which alternates between a central white vase silhouette against a dark background and two symmetrical black profiles of facing human heads against a light background. Developed by Danish Edgar Rubin in his 1915 doctoral on , the design relies on a shared contour that serves as the boundary for either the vase or the profiles, with perceptual dominance shifting involuntarily as the brain reassigns figure-ground organization. The alternation highlights how proximity, , and principles compete in determining which region is perceived as the foreground object. The present a depth in architectural form, depicted as a two-dimensional line drawing of a staircase that can be interpreted as ascending from left to right or descending from right to left. Introduced by German natural scientist Heinrich G. F. Schroeder in 1858 in the journal , the stimulus uses converging parallel lines to suggest perspective without specifying the viewpoint, leading to perceptual flips between the two orientations as the observer's interpretation of the implied changes. This bistable reversal underscores the role of incomplete depth cues in fostering multistability. Motion-based examples include the ambiguous cylinder illusion, where a rotating three-dimensional object constructed from black-and-white striped segments appears to transform between a horizontal cylinder rolling side-to-side and a vertical cylinder rolling up-and-down depending on the viewing angle. Created by Japanese mathematician Kokichi Sugihara and recognized in the 2016 Best Illusion of the Year contest, the design leverages specular highlights and luminance contrasts on the surfaces to create conflicting motion and shape interpretations that alternate as the object turns. Similarly, plaid motion stimuli consist of two overlapping sinusoidal gratings moving in different directions, perceived either as a single coherent pattern translating along their vector sum (coherent motion) or as two independent transparent surfaces sliding over each other (component motion). First systematically studied by Edward H. Adelson and J. Anthony Movshon in 1982, these stimuli reveal directional ambiguity resolved by integration mechanisms in the visual cortex, with switches occurring under conditions of low coherence or attention shifts. Figure-ground organization also drives multistability in variants of the Kanizsa triangle, where pac-man-shaped inducers arranged at the corners create illusory contours forming a central that can reverse such that the "white" triangle becomes the background and the surrounding disk fragments emerge as the figure. Originating from Gaetano Kanizsa's 1955 experiments on quasi-perceptual margins, these variants incorporate bistable boundaries by adjusting inducer sizes or contrasts, allowing the illusory shape to flip between occluded object and subjective surface interpretations. In real-world contexts, multistable perception arises with the moon's s, which can appear as concave depressions under typical earthshine illumination or as convex domes if the lighting direction is mentally inverted or shadowed differently. This shape-from- ambiguity, noted in perceptual studies since the , stems from the brain's default assumption of overhead lighting, leading to alternations when cues conflict, as demonstrated in psychophysical experiments with inverted crater images. Ambiguous wireframe objects extend this to polyhedral forms beyond the , such as wireframe tetrahedrons or dodecahedrons, where line junctions permit multiple valid 3D embeddings that flip between orientations lacking disambiguating textures or . These stimuli, explored in computational vision models since the , illustrate how sparse edge information alone suffices for perceptual in naturalistic wire sculptures or diagrams.

Non-Visual Instances

Multistable perception extends beyond vision to auditory modalities, where ambiguous stimuli presented dichotically to each can lead to alternating dominance of one auditory stream over the other. In paradigms, such as those involving competing tones or speech fragments, listeners experience spontaneous switches between perceiving a single integrated sound or segregated streams, akin to visual dynamics. For instance, in tonal rivalry tasks, two concurrent tone sequences of differing pitches (e.g., high-pitch at 1008 Hz versus low-pitch at 400 Hz) are presented, prompting observers to report alternations in which pitch sequence dominates as the foreground percept. These auditory multistabilities highlight competition between perceptual groupings, with switch rates influenced by factors like and stimulus coherence, paralleling visual multistability but adapted to temporal auditory processing. In the olfactory domain, binaral rivalry occurs when dissimilar odorants are simultaneously delivered to each nostril, resulting in perceptual alternations between the scents. Pioneering studies demonstrated this by presenting and odors binasally, where participants reported exclusive dominance of one odor at a time, with spontaneous reversals, reflecting rivalry at both peripheral (receptor) and central cortical levels. This phenomenon underscores olfactory multistability's reliance on mechanisms, similar to visual suppression, and has been shown to interact with other senses, such as modulating visual rivalry when odors are nostril-specific. Binaral rivalry thus provides a model for understanding how the resolves competing olfactory inputs in natural environments, like mixed scents. Tactile multistability manifests in paradigms inducing ambiguous apparent motion on the skin, where stimuli create between competing directional interpretations. A seminal demonstration used a tactile apparent-motion —four vibrotactile points sequentially activated on the fingertip—leading to spontaneous reversals between horizontal and vertical motion percepts, with average interswitch intervals of 31.9 seconds (SD = 14.6 seconds). These reversals occur without external cues, driven by internal neural , and can be biased by attentional focus or prior adaptation. Variants of the rubber hand illusion further illustrate tactile ownership multistability, where conflicting visuotactile synchrony on real and fake hands prompts alternating feelings of embodiment, though less spontaneously than pure setups. Such examples reveal tactile perception's capacity for bistable organization, emphasizing cross-modal parallels in sensory . Cross-modal multistability arises in audiovisual speech integration, where conflicting auditory and visual cues elicit perceptual alternations or fusions. Extensions of the , involving bistable speech stimuli like ambiguous syllables paired with incongruent lip movements (e.g., auditory /ba/ with visual /ga/), lead to switches between integrated illusions (e.g., perceiving /da/) and segregated auditory dominance. In rivalry scenarios, such as dichoptic presentation of competing facial articulations with binaural speech, observers experience dominance alternations favoring one modality, with visual cues often suppressing auditory percepts temporarily. These interactions demonstrate how multistability resolves sensory conflicts in communication, with neural correlates involving activity. Rare instances of multistability appear in language processing, particularly with semantic and syntactic that trigger perceptual flips between interpretations. This reanalysis involves between structural parses, with lingering effects from the initial ambiguity, and has been linked to broader semantic multistability in ambiguous words or phrases where multiple meanings alternate in awareness. Such linguistic phenomena illustrate how higher-level cognitive processes can exhibit multistable dynamics, bridging low-level sensory rivalry with interpretive .

Research and Applications

Experimental Methods

Experimental methods for studying multistable perception primarily rely on controlled presentations of ambiguous stimuli to elicit perceptual alternations, with techniques designed to measure switches objectively while minimizing confounds like verbal reporting. Core paradigms include binocular rivalry, where incompatible images are presented dichoptically to each eye, often using a to align the stimuli in a common and induce alternations between the two monocular views. Another key approach is continuous flash suppression (CFS), in which a dynamic, high-contrast Mondrian pattern presented to one eye suppresses a static stimulus to the other, allowing investigation of unconscious processing and no-report measures of breakthrough into awareness. Measurement tools encompass behavioral and neurophysiological techniques to track perceptual states. Forced-choice reporting requires participants to indicate their dominant percept via button presses or verbal responses at regular intervals or upon detected switches, providing a direct but subjective index of rivalry dynamics. Eye-tracking methods monitor saccades or microsaccades, which often precede or correlate with perceptual reversals, offering an objective, no-report proxy for switches without interrupting the viewing task. Electrophysiological tools like (EEG) and (MEG) capture neural correlates, such as event-related potentials or oscillatory changes in alpha or gamma bands, that align with perceptual transitions during rivalry. Advanced methods have emerged to address limitations of traditional reporting. No-report paradigms, developed in the 2020s, infer perceptual states from involuntary behavioral markers like fixation shifts or pupil dilations, reducing confounds from metacognitive processes and enabling purer . (VR) headsets facilitate immersive presentations of ambiguous scenes, such as rotating cylinders or depth-inverted stimuli, to study multistability in ecologically valid, three-dimensional contexts while maintaining precise control over dichoptic stimulation. To manipulate and isolate factors influencing perceptual dynamics, such as reversal rates, experiments control variables like stimulus duration—shorter exposures yield fewer alternations, while longer ones stabilize rates—and tasks, where directing focus to one percept via concurrent demands slows switches or prolongs dominance.

Implications and Recent Findings

Multistable serves as a key model for understanding , particularly through , where alternating percepts highlight the neural mechanisms underlying perceptual without changes in sensory input. Recent studies from 2021 to 2025 have emphasized 's role in revealing the dynamic selection processes that gate conscious experience, with theoretical models integrating recurrent processing and to explain how the brain resolves ambiguity. For instance, a 2025 review of bistable outlines how techniques in probe the neural correlates of , including challenges with no-report paradigms that may reflect conscious disengagement rather than direct correlates. Advancements in visualizing brain-wide patterns have further illuminated these processes, with a 2025 study from the applying geometric visualization techniques to map activity changes during tasks, revealing structured spatiotemporal dynamics that align with perceptual transitions. This approach highlights how distributed cortical networks synchronize to stabilize or alternate interpretations, offering insights into the global integration required for conscious vision. Such findings extend to 2021-2025 research showing that rivalry-induced conflicts engage the anterior insula to signal perceptual mismatches, linking multistability to broader cognitive control mechanisms. In clinical contexts, multistable perception has emerged as a potential biomarker for psychiatric disorders, with slower rivalry alternation rates observed in patients with , obsessive-compulsive disorder, major depression, and compared to healthy controls. A 2019 study, corroborated in subsequent research through 2024, attributes this slowing to shared neurochemical imbalances, such as reduced excitatory-inhibitory balance, enabling rivalry rate variability as a trait marker for vulnerability to mood and psychotic conditions, though findings vary across paradigms like structure-from-motion bi-stability. Therapeutically, perceptual training paradigms leveraging multistability have shown promise in enhancing , as demonstrated in a 2016 study extended by recent applications, where repeated exposure to rivalry stimuli improves top-down modulation and reduces fixation biases in attention-deficit contexts. In artificial intelligence and computational modeling, recent developments integrate adaptation mechanisms to mimic human multistability, with a 2024 neurocognitive model simulating rivalry through recurrent neural networks that account for sensory adaptation and noise-driven switches. This model bridges neuroscience and AI by reproducing behavioral patterns like history-dependent dominance periods, where prior percepts bias future alternations, as explored in 2025 research on layered cortical structures. A 2024 Nature study further links imagination to perception, showing that mental imagery can bias rivalry outcomes via shared representational spaces in visual cortex, informing hybrid AI systems that incorporate top-down priors. Broader implications suggest an evolutionary role for multistability in promoting flexible perception, allowing adaptive responses to ambiguous environments through value-based internal foraging, as posited in 2022 analyses. However, gaps persist in AI, with a 2025 Temple University study revealing that human visual object recognition, even in young children, vastly outperforms current models in data efficiency and handling perceptual ambiguity, underscoring the need for biologically inspired architectures to achieve human-like robustness.

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