Bistable Perception Research Articles

Differential effects of stimulus strength and volitional control in bistable perception

Bistable perception has been widely studied in the visual system where ambiguity in sensory information coming from, for example, binocular, depth or motion cues leads to spontaneous shifts in perception. Indeed, modeling of rivalrous dynamics induced by ambiguity in these visual sensory cues led to a generalized Levelt’s proposition II that describes the effect of stimulus strength manipulations around equidominance: ``the mean dominance duration of the stronger percept changes more than that of the weaker percept'' [1]. In [2] it was shown that auditory and visual bistability share the common traits of perceptual bistability using ambiguous auditory streaming and visual motion stimuli. In each modality there are alternations between a grouped percept and a split percept. They further investigated the effect of volitional control at equidominance and found that attending to one percept (grouped or split) reduced mean dominance durations of the unattended (weaker) percept. These findings are incompatible with the generalized Levelt’s Proposition II if one assumes that volition increases the strength of the targeted percept. We propose a volitional mechanism with state-dependent inputs in order to resolve this apparent conflict. We work with a widely used competition model (Fig ​(Fig1A)1A) for bistable dynamics that incorporates mutual inhibition and slow adaptation [3]. We incorporate input normalization as proposed in [1]. Symmetry is assumed between the competing percepts such that when input to each population is balanced the alternations generated by the model are at equidominance. When the input is increased to population #1, more time is spent with #1 active (Fig ​(Fig1B).1B). Furthermore, #1’s percept duration changes the most given more input, which is consistent with generalized Levelt's II. Figure 1 A Model schematic: u1 and u2 are competing populations with inputs I1, I2 and adaptation variables a1, a2. Volitional bias Iv with strength K is active when u2 active (controlled by a threshold function S). B Durations for u1 active (T1) and for u2 active ... The underlying concept of our proposed mechanism for volitional control is that when, say, percept #1 is given a bias, population #1 will receive additional input, but only when the competing #2 is active (Fig ​(Fig1A,1A, red). We assume that this volitional bias is active only when the competing population’s activity is above some threshold. We find a qualitatively different relationship (than in Levelt II) between volitional bias and the durations. Notably durations for the percept receiving volitional bias are unchanged, whereas, the durations for the weaker percept drop significantly.These results are consistent with [2] for experimental conditions where subjects exert volitional towards a particular percept.

Critical slowing down and noise-induced intermittency in bistable perception: bifurcation analysis.

Stochastic dynamics and critical slowing down were studied experimentally and numerically near the onset of dynamical bistability in visual perception under the influence of noise. Exploring the Necker cube as the essential example of an ambiguous figure, and using its wire contrast as a control parameter, we measured dynamical hysteresis in two coexisting percepts as a function of both the velocity of the parameter change and the background luminance. The bifurcation analysis allowed us to estimate the level of cognitive noise inherent to brain neural cells activity, which induced intermittent switches between different perception states. The results of numerical simulations with a simple energy model are in good qualitative agreement with psychological experiments.

Multisensory constraints on awareness

Given that multiple senses are often stimulated at the same time, perceptual awareness is most likely to take place in multisensory situations. However, theories of awareness are based on studies and models established for a single sense (mostly vision). Here, we consider the methodological and theoretical challenges raised by taking a multisensory perspective on perceptual awareness. First, we consider how well tasks designed to study unisensory awareness perform when used in multisensory settings, stressing that studies using binocular rivalry, bistable figure perception, continuous flash suppression, the attentional blink, repetition blindness and backward masking can demonstrate multisensory influences on unisensory awareness, but fall short of tackling multisensory awareness directly. Studies interested in the latter phenomenon rely on a method of subjective contrast and can, at best, delineate conditions under which individuals report experiencing a multisensory object or two unisensory objects. As there is not a perfect match between these conditions and those in which multisensory integration and binding occur, the link between awareness and binding advocated for visual information processing needs to be revised for multisensory cases. These challenges point at the need to question the very idea of multisensory awareness.

Methods to explore the influence of top-down visual processes on motor behavior.

Kinesthetic awareness is important to successfully navigate the environment. When we interact with our daily surroundings, some aspects of movement are deliberately planned, while others spontaneously occur below conscious awareness. The deliberate component of this dichotomy has been studied extensively in several contexts, while the spontaneous component remains largely under-explored. Moreover, how perceptual processes modulate these movement classes is still unclear. In particular, a currently debated issue is whether the visuomotor system is governed by the spatial percept produced by a visual illusion or whether it is not affected by the illusion and is governed instead by the veridical percept. Bistable percepts such as 3D depth inversion illusions (DIIs) provide an excellent context to study such interactions and balance, particularly when used in combination with reach-to-grasp movements. In this study, a methodology is developed that uses a DII to clarify the role of top-down processes on motor action, particularly exploring how reaches toward a target on a DII are affected in both deliberate and spontaneous movement domains.

Revisiting the Lissajous figure as a tool to study bistable perception

During bistable vision perception spontaneously "switches" between two mutually exclusive percepts despite constant sensory input. The endogenous nature of these perceptual transitions has motivated extensive research aimed at the underlying mechanisms, since spontaneous perceptual transitions of bistable stimuli should in principle allow for a dissociation of processes related to sensory stimulation from those related to conscious perception. However, transitions from one conscious percept to another are often not instantaneous, and participants usually report a considerable amount of mixed or unclear percepts. This feature of bistable vision makes it difficult to isolate transition-related visual processes. Here, we revisited an ambiguous depth-from-motion stimulus which was first introduced to experimental psychology more than 80 years ago. This rotating Lissajous figure might prove useful in complementing other bistable stimuli, since its perceptual transitions only occur at critical stimulus configurations and are virtually instantaneous, thus facilitating the construction of a perceptually equivalent replay condition. We found that three parameters of the Lissajous figure - complexity, line width, and rotational speed - differentially modulated its perceptual dominance durations and transition probabilities, thus providing experimenters with a versatile tool to study the perceptual dynamics of bistable vision.

Performance-based and subjective measures of perceptual organization in humans

Measures of auditory perceptual organization in humans have traditionally relied on subjective reports from subjects. For instance, in alternating tone sequences, subjects might be asked to report whether they hear one or two streams. In order to investigate perceptual organization in non-human species, it can be useful to devise tests that are more objective, in that they have a right and a wrong answer and do not rely on introspection. Recent studies from our laboratory have employed various objective and subjective tasks to provide converging evidence in the search for the underlying principles of auditory perceptual organization. It is suggested that different tasks can bias potentially multi-stable percepts in one way or another, which in turn may be useful in uncovering neural correlates of perceptual organization that can vary even when the acoustic stimuli remain the same. [Work supported by NIH grant R01DC007657.]

Noise and adaptation in multistable perception: Noise drives when to switch, adaptation determines percept choice

We study the dynamics of perceptual switching in ambiguous visual scenes that admit more than two interpretations/percepts to gain insight into the dynamics of perceptual multistability and its underlying neural mechanisms. We focus on visual plaids that are tristable and we present both experimental and computational results. We develop a firing-rate model based on mutual inhibition and adaptation that involves stochastic dynamics of multiple-attractor systems. The model can account for the dynamic properties (transition probabilities, distributions of percept durations, etc.) observed in the experiments. Noise and adaptation have both been shown to play roles in the dynamics of bistable perception. Here, tristable perception allows us to specify the roles of noise and adaptation in our model. Noise is critical in considering the time of a switch. On the other hand, adaptation mechanisms are critical in considering perceptual choice (in tristable perception, each time a percept ends, there is a possible choice between two new percepts).

Binocular Rivalry: Frontal Activity Relates to Introspection and Action But Not to Perception

When two dissimilar stimuli are presented to the eyes, perception alternates between multiple interpretations, a phenomenon dubbed binocular rivalry. Numerous recent imaging studies have attempted to unveil neural substrates underlying multistable perception. However, these studies had a conceptual constraint: access to observers' perceptual state relied on their introspection and active report. Here, we investigated to what extent neural correlates of binocular rivalry in healthy humans are confounded by this subjective measure and by action. We used the optokinetic nystagmus and pupil size to objectively and continuously map perceptual alternations for binocular-rivalry stimuli. Combining these two measures with fMRI allowed us to assess the neural correlates of binocular rivalry time locked to the perceptual alternations in the absence of active report. When observers were asked to actively report their percept, our objective measures matched the report. In this active condition, objective measures and subjective reporting revealed that occipital, parietal, and frontal areas underlie the processing of binocular rivalry, replicating earlier findings. Furthermore, objective measures provided additional statistical power due to their continuous nature. Importantly, when observers passively experienced rivalry without reporting perceptual alternations, a different picture emerged: differential neural activity in frontal areas was absent, whereas activation in occipital and parietal regions persisted. Our results question the popular view of a driving role of frontal areas in the initiation of perceptual alternations during binocular rivalry. Instead, we conclude that frontal areas are associated with active report and introspection rather than with rivalry per se.

In Search of Causal Mechanisms Underlying Bistable Perception

The visual system interprets most visual scenes according to a single best interpretation, thereby effectively disambiguating the inherently ambiguous information provided by retinal stimulation. The phenomenal instability of ambiguous figures like the Necker cube provides an especially dramatic and

The linear impact of concurrent working memory load on dynamics of Necker cube perceptual reversals

Ambiguous figures are visual stimuli that may be perceived in multistable interpretations. The role of attention in modulating perceptual reversals of ambiguous stimuli is not clear. We tested whether perceptual reversals depend on working memory by manipulating its load while the participants were viewing the Necker cube. Increasing working memory load delayed the latency and decreased the frequency of reversals. These effects followed a linear function of load. The findings imply shared resources of the mechanisms responsible for perceptual reversals and working memory maintenance. However, reversals were not completely abolished even with the hard seven-consonants load, suggesting that bottom-up processes continue to operate in the bistable perception dynamics when top-down mechanisms are attenuated.

Stable individual characteristics in the perception of multiple embedded patterns in multistable auditory stimuli

The ability of the auditory system to parse complex scenes into component objects in order to extract information from the environment is very robust, yet the processing principles underlying this ability are still not well understood. This study was designed to investigate the proposal that the auditory system constructs multiple interpretations of the acoustic scene in parallel, based on the finding that when listening to a long repetitive sequence listeners report switching between different perceptual organizations. Using the “ABA-” auditory streaming paradigm we trained listeners until they could reliably recognize all possible embedded patterns of length four which could in principle be extracted from the sequence, and in a series of test sessions investigated their spontaneous reports of those patterns. With the training allowing them to identify and mark a wider variety of possible patterns, participants spontaneously reported many more patterns than the ones traditionally assumed (Integrated vs. Segregated). Despite receiving consistent training and despite the apparent randomness of perceptual switching, we found individual switching patterns were idiosyncratic; i.e., the perceptual switching patterns of each participant were more similar to their own switching patterns in different sessions than to those of other participants. These individual differences were found to be preserved even between test sessions held a year after the initial experiment. Our results support the idea that the auditory system attempts to extract an exhaustive set of embedded patterns which can be used to generate expectations of future events and which by competing for dominance give rise to (changing) perceptual awareness, with the characteristics of pattern discovery and perceptual competition having a strong idiosyncratic component. Perceptual multistability thus provides a means for characterizing both general mechanisms and individual differences in human perception.

Rotating goblet and talking profiles: does a rotating goblet increase the figural dominance of profiles in Rubin's type of figure-ground reversal patterns?

We present a novel three-dimensional (3-D) version of Rubin's classical bistable goblet-profiles figure. An actual goblet sculpture was produced and rotated on a turntable in front of a white background. As the goblet rotates about its central axis, small circular asymmetries around the lips and chin region give a clear impression of two white profiles talking to each other. Although the profiles actually correspond to empty space or white background, they are more likely to be perceived as 'figure' than the 3-D goblet itself. Four experiments that presented the actual goblet (experiment 1) or two-dimensional (2-D) movies of it (experiments 2-4) were designed to verify these observations. We measured perceptual dominance of profiles as 'figure' and rate of reversal as a function of three factors: motion (static vs rotating), orientation (upright vs inverted), and configuration (face-to-face vs back-to-back). Results for the rotating goblet showed a statistically reliable preference for perceiving the talking profiles as 'figure'. Deforming the profiles by manipulating the vertex angle of the mouth region produced an inverted U-shaped curve with the peak representing the stimulus condition in which the profiles perception was most remarkable. We discussed a number of 3-D and 2-D figure-ground factors that might apply to this rather complex stimulus situation.

A more realistic quantum mechanical model of conscious perception during binocular rivalry

A more realistic quantum mechanical model of conscious perception during binocular rivalry

Neural substrates of perceptual integration during bistable object perception

The way we perceive an object depends both on feedforward, bottom-up processing of its physical stimulus properties and on top-down factors such as attention, context, expectation, and task relevance. Here we compared neural activity elicited by varying perceptions of the same physical image--a bistable moving image in which perception spontaneously alternates between dissociated fragments and a single, unified object. A time-frequency analysis of EEG changes associated with the perceptual switch from object to fragment and vice versa revealed a greater decrease in alpha (8-12 Hz) accompanying the switch to object percept than to fragment percept. Recordings of event-related potentials elicited by irrelevant probes superimposed on the moving image revealed an enhanced positivity between 184 and 212 ms when the probes were contained within the boundaries of the perceived unitary object. The topography of the positivity (P2) in this latency range elicited by probes during object perception was distinct from the topography elicited by probes during fragment perception, suggesting that the neural processing of probes differed as a function of perceptual state. Two source localization algorithms estimated the neural generator of this object-related difference to lie in the lateral occipital cortex, a region long associated with object perception. These data suggest that perceived objects attract attention, incorporate visual elements occurring within their boundaries into unified object representations, and enhance the visual processing of elements occurring within their boundaries. Importantly, the perceived object in this case emerged as a function of the fluctuating perceptual state of the viewer.

Priming effects under continuous flash suppression: An examination on subliminal bottom‐up processing

AbstractBinocular rivalry is a bistable perception that occurs when two dissimilar stimuli are presented to each eye. Recent studies have demonstrated that the reaction time to target words under binocular rivalry was shortened when semantically related prime words were presented supraliminally (Costello, Jiang, Baartman, McGlennen, & He, 2009). We investigated whether three types of priming (repetition, semantic, and cross‐script) occurred from the prime words presented under binocular rivalry, by using continuous flash suppression paradigm (Tsuchiya, Koch, Gilroy, & Blake, 2006). The prime words presented to the suppressed eye invoked repetition and cross‐script priming, but not semantic priming. The results suggested that the stimuli presented to the suppressed eye underwent shape and phonological level processing, but not semantic level processing.

To adapt or not to adapt: The question of domain-general cognitive control

What do perceptually bistable figures, sentences vulnerable to misinterpretation and the Stroop task have in common? Although seemingly disparate, they all contain elements of conflict or ambiguity. Consequently, in order to monitor a fluctuating percept, reinterpret sentence meaning, or say “blue” when the word RED is printed in blue ink, individuals must regulate attention and engage cognitive control. According to the Conflict Monitoring Theory (Botvinick, Braver, Barch, Carter, & Cohen, 2001), the detection of conflict automatically triggers cognitive control mechanisms, which can enhance resolution of subsequent conflict, namely, “conflict adaptation.” If adaptation reflects the recruitment of domain-general processes, then conflict detection in one domain should facilitate conflict resolution in an entirely different domain. We report two novel findings: (i) significant conflict adaptation from a syntactic to a non-syntactic domain and (ii) from a perceptual to a verbal domain, providing strong evidence that adaptation is mediated by domain-general cognitive control.

Frontoparietal Cortex Mediates Perceptual Transitions in Bistable Perception

During bistable vision, perception oscillates between two mutually exclusive percepts despite constant sensory input. Greater BOLD responses in frontoparietal cortex have been shown to be associated with endogenous perceptual transitions compared with "replay" transitions designed to closely match bistability in both perceptual quality and timing. It has remained controversial, however, whether this enhanced activity reflects causal influences of these regions on processing at the sensory level or, alternatively, an effect of stimulus differences that result in, for example, longer durations of perceptual transitions in bistable perception compared with replay conditions. Using a rotating Lissajous figure in an fMRI experiment on 15 human participants, we controlled for potential confounds of differences in transition duration and confirmed previous findings of greater activity in frontoparietal areas for transitions during bistable perception. In addition, we applied dynamic causal modeling to identify the neural model that best explains the observed BOLD signals in terms of effective connectivity. We found that enhanced activity for perceptual transitions is associated with a modulation of top-down connectivity from frontal to visual cortex, thus arguing for a crucial role of frontoparietal cortex in perceptual transitions during bistable perception.

The Necker–Zeno Model for Bistable Perception

A novel conceptual framework for theoretical psychology is presented and illustrated for the example of bistable perception. A basic formal feature of this framework is the non-commutativity of operations acting on mental states. A corresponding model for the bistable perception of ambiguous stimuli, the Necker-Zeno model, is sketched and some empirical evidence for it so far is described. It is discussed how a temporal non-locality of mental states, predicted by the model, can be understood and tested.

Bifurcation study of a neural field competition model with an application to perceptual switching in motion integration.

Perceptual multistability is a phenomenon in which alternate interpretations of a fixed stimulus are perceived intermittently. Although correlates between activity in specific cortical areas and perception have been found, the complex patterns of activity and the underlying mechanisms that gate multistable perception are little understood. Here, we present a neural field competition model in which competing states are represented in a continuous feature space. Bifurcation analysis is used to describe the different types of complex spatio-temporal dynamics produced by the model in terms of several parameters and for different inputs. The dynamics of the model was then compared to human perception investigated psychophysically during long presentations of an ambiguous, multistable motion pattern known as the barberpole illusion. In order to do this, the model is operated in a parameter range where known physiological response properties are reproduced whilst also working close to bifurcation. The model accounts for characteristic behaviour from the psychophysical experiments in terms of the type of switching observed and changes in the rate of switching with respect to contrast. In this way, the modelling study sheds light on the underlying mechanisms that drive perceptual switching in different contrast regimes. The general approach presented is applicable to a broad range of perceptual competition problems in which spatial interactions play a role.

The influence of dopamine‐related genes on perceptual stability

Bistable perception is the spontaneous and automatic alternation between two different perceptual states that occurs when sensory information is ambiguous. Perceptual alternation rates are robust within individuals but vary substantially between individuals. Slowed perceptual switching has been consistently reported in patients with bipolar disorder (BPD) and has been suggested as a trait marker for this disease. Although genetic factors have been implicated in both BPD and bistable perception, the underlying biological mechanisms that mediate the observed perceptual stability in BPD remain elusive. Here, we tested the effect of two variable number tandem repeat (VNTR) polymorphisms in DRD4 and DAT1 (SLC6A3), both candidate genes for BPD with functional impact on dopaminergic neurotransmission, on bistable perception in a cohort of 108 healthy human subjects. The BPD risk allele DRD4-2R was significantly associated with slow perceptual switching. There was no effect of DAT1 genotype on bistable perception. Our findings indicate that genetic differences in dopaminergic neurotransmission linked to BPD also account for interindividual variability in bistable perception, thus providing a genetic basis for perceptual stability as a trait marker of BPD.