Multistable Perception

Multistable perception is produced by stimuli that are consistent with two or more different comparably likely perceptual interpretations. After the initial perception is resolved in favor of one of the interpretations, continued viewing leads to fluctuating subjective experience, as perception spontaneously switches between alternative states. Multistable perception occurs for different modalities, including visual, auditory, tactile, olfactory perception and proprioception, and various conflicting sensory representations, such as eye dominance, depth, motion, or meaning. Despite large differences, multistable stimuli produce quantitatively similar perceptual experience with stereotypical distribution of durations of dominance phases, similar dependence on the absolute and relative strength of competing perceptual interpretations, prior perceptual history, presentation method, attention, and volitional control, and so on. Taken together, this shows that multistable perception reflects the action of general canonical perceptual mechanisms whose purpose is to resolve the conflicting evidence and ensure a single dominant perception that can be used for action. Thus, it informs us about mechanisms of perceptual decision making, including the importance of feedback mechanisms in resolving perceptual ambiguity and the role of parietal and frontal regions in facilitating changes in perception. Multistable perception provides useful constraints for models, inspiring a plethora of models of perception that combine neurally plausible mechanisms, such as neural adaptation and inhibition, or are based on the idea of predictive coding. The sensitive nature of multistable perception makes a valuable experimental tool that can reveal even minor differences due to low- or high-level influences, including genetic or clinical cases. As such, it is an important tool in studying neural and behavioral correlates of consciousness as it dissociates perception from the stimulus.

Binocular rivalry reveals an out-of-equilibrium neural dynamics suited for decision-making

In ambiguous or conflicting sensory situations, perception is often ‘multistable’ in that it perpetually changes at irregular intervals, shifting abruptly between distinct alternatives. The interval statistics of these alternations exhibits quasi-universal characteristics, suggesting a general mechanism. Using binocular rivalry, we show that many aspects of this perceptual dynamics are reproduced by a hierarchical model operating out of equilibrium. The constitutive elements of this model idealize the metastability of cortical networks. Independent elements accumulate visual evidence at one level, while groups of coupled elements compete for dominance at another level. As soon as one group dominates perception, feedback inhibition suppresses supporting evidence. Previously unreported features in the serial dependencies of perceptual alternations compellingly corroborate this mechanism. Moreover, the proposed out-of-equilibrium dynamics satisfies normative constraints of continuous decision-making. Thus, multistable perception may reflect decision-making in a volatile world: integrating evidence over space and time, choosing categorically between hypotheses, while concurrently evaluating alternatives.

Multistable Perception in Older Adults: Constructing a Whole from Fragments

Visual perception is constructive in nature; that is, a coherent whole is generated from ambiguous fragments that are encountered in dynamic visual scenes. Creating this coherent whole from fragmented sensory inputs requires one to detect, identify, distinguish and organize sensory input. The organization of fragments into a coherent whole is facilitated by the continuous interactions between lower level sensory inputs and higher order processes. However, age-related declines are found in both neural structures and cognitive processes (e.g., attention and inhibition). The impact of these declines on the constructive nature of visual processing was the focus of this study. Here we asked younger adults, young-old (65–79 years), and old-old adults (80+ years) to view a multistable figure (i.e., Necker cube) under four conditions (free, priming, volition, and adaptation) and report, via a button press, when percepts spontaneously changed. The oldest-olds, unlike young-olds and younger adults, were influenced by priming, had less visual stability during volition and showed less ability to adapt to multistable stimuli. These results suggest that the ability to construct a coherent whole from fragments declines with age. More specifically, vision is constructed differently in the old-olds, which might influence environmental interpretations and navigational abilities in this age group.

Multistable Perception in Older Adults: Constructing a Whole from Fragments

Visual perception is constructive in nature; that is, a coherent whole is generated from ambiguous fragments that are encountered in dynamic visual scenes. Creating this coherent whole from fragmented sensory inputs requires one to detect, identify, distinguish and organize sensory input. The organization of fragments into a coherent whole is facilitated by the continuous interactions between lower level sensory inputs and higher order processes. However, age-related declines are found in both neural structures and cognitive processes (e.g., attention and inhibition). The impact of these declines on the constructive nature of visual processing was the focus of this study. Here we asked younger adults, young-old (65–79 years), and old-old adults (80+ years) to view a multistable figure (i.e., Necker cube) under four conditions (free, priming, volition, and adaptation) and report, via a button press, when percepts spontaneously changed. The oldest-olds, unlike young-olds and younger adults, were influenced by priming, had less visual stability during volition and showed less ability to adapt to multistable stimuli. These results suggest that the ability to construct a coherent whole from fragments declines with age. More specifically, vision is constructed differently in the old-olds, which might influence environmental interpretations and navigational abilities in this age group.

Separable pupillary signatures of perception and action during perceptual multistability

The pupil provides a rich, non-invasive measure of the neural bases of perception and cognition. It can particularly inform about the role of arousal-linked neuromodulation, which alters both cortical processing and pupil size. But a multitude of factors influence pupil size, which complicates interpretation. We measured pupil signals accompanying changes in multistable perception, i.e. accompanying endogenously-generated perceptual changes in the face of inconclusive sensory input. Perceptual changes were marked by a complex pupil response that could be decomposed into two components: a dilation tied to task execution and plausibly reflecting arousal-linked noradrenaline, and an overlapping constriction tied to the perceptual transient and plausibly reflecting altered cortical responses. Constriction, but not dilation, amplitude depended on the timing of perceptual changes, possibly providing an index of neural adaptation. We conclude that pupil size reflects several dissociable processes during perceptual multistability, and that arousal-linked neuromodulation shapes action but not perception in these circumstances.

History-dependent changes of Gamma distribution in multistable perception

Multistable perception – spontaneous switches of perception when viewing a stimulus compatible with several distinct interpretations – is often characterized by the distribution of durations of individual dominance phases. For continuous viewing conditions, these distributions look remarkably similar for various multistable displays and are typically described using Gamma distribution. Moreover, durations of individual dominance phases show a subtle but consistent dependence on prior perceptual experience with longer dominance phases tending to increase the duration of the following ones, whereas the shorter dominance leads to similarly shorter durations. One way to generate similar switching behavior in a model is by using a combination of cross-inhibition, self-adaptation, and neural noise with multiple useful models being built on this principle. Here, we take a closer look at the history-dependent changes in the distribution of durations of dominance phases. Specifically, we used Gamma distribution and allowed both its parameters – shape and scale – to be linearly dependent on the prior perceptual experience at two timescales. We fit a hierarchical Bayesian model to five datasets that included binocular rivalry, Necker cube, and kinetic-depth effects displays, as well as data on binocular rivalry in children and on binocular rivalry with modulated contrast. For all datasets, we found a consistent change of the distribution shape with higher levels of perceptual history, which can be viewed as a proxy for perceptual adaptation, leading to a more normal-like shape of the Gamma distribution. When comparing real observers to matched simulated dominance phases generated by a spiking neural model of bistability, we found that although it matched the positive history-dependent shift in the shape parameter, it also predicted a negative change of scale parameter that did not match empirical data. We argue that our novel analysis method, the implementation is available freely at the online repository, provides additional constraints for computational models of multistability.Author SummaryMultistable perception occurs when one continuously views a figure that can be seen in two distinct ways. A classic old-young woman painting, a face-vase figure, or a Necker cube are examples easy to find online. The endless spontaneous switches of your perception between the alternatives inform us about the interplay of various forces that shape it. One way to characterize these switches is by looking at their timing: How long was a particular image dominant, how did that reflect what you have seen previously, the focus of your attention, or the version of the figure that we showed you? This knowledge allows us to build models of perception and test them against the data we collected. As models grow more elaborate, we need to make tests more elaborate as well and for this, we require more precise and specific ways to characterize your perception. Here, we demonstrate how your recent perceptual experience – which of the alternative images did you see and for how long – predicts subtle but consistent changes in the shape of the distribution that describes perceptual switching. We believe it to be a more stringent test by demonstrating how a classical model of bistability fails on it.

Instability with a purpose: how the visual brain makes decisions in a volatile world

In ambiguous or conflicting sensory situations, perception is often ‘multistable’ in that it changes abruptly at irregular intervals, shifting perpetually between distinct alternatives. Intriguingly, the interval statistics of these alternations exhibits quasi-universal characteristics, suggesting a general mechanism. Here we show that the stereotypical features of multistable perception, exemplified by binocular rivalry, are reproduced in detail by a hierarchical dynamics operating out of equilibrium. Its constitutive elements are discretely stochastic and idealize the metastability of cortical networks. Independent elements accumulate visual evidence at one level, while groups of coupled elements compete for dominance at another level. As soon as one group dominates perception, feedback inhibition suppresses supporting evidence. This mechanism is corroborated compellingly by unexpected serial dependencies of perceptual alternations. Moreover, it satisfies normative constraints of continuous decision-making. We conclude that multistable perception reflects decision-making in a volatile world: integrating evidence over space and time, choosing categorically between hypotheses, while concurrently evaluating alternatives.

Decoding the contents of consciousness from prefrontal ensembles

ABSTRACTMultiple theories attribute to the primate prefrontal cortex a critical role in conscious perception. However, opposing views caution that prefrontal activity could reflect other cognitive variables during paradigms investigating consciousness, such as decision-making, monitoring and motor reports. To resolve this ongoing debate, we recorded from prefrontal ensembles of macaque monkeys during a no-report paradigm of binocular rivalry that instigates internally driven transitions in conscious perception. We could decode the contents of consciousness from prefrontal ensemble activity during binocular rivalry with an accuracy similar to when these stimuli were presented without competition. Oculomotor signals, used to infer conscious content, were not the only source of these representations since visual input could be significantly decoded when eye movements were suppressed. Our results suggest that the collective dynamics of prefrontal cortex populations reflect internally generated changes in the content of consciousness during multistable perception.One sentence summaryNeural correlates of conscious perception can be detected and perceptual contents can be reliably decoded from the spiking activity of prefrontal populations.