39 research outputs found
A predictive coding account of bistable perception - a model-based fMRI study
In bistable vision, subjective perception wavers between two interpretations
of a constant ambiguous stimulus. This dissociation between conscious
perception and sensory stimulation has motivated various empirical studies on
the neural correlates of bistable perception, but the neurocomputational
mechanism behind endogenous perceptual transitions has remained elusive. Here,
we recurred to a generic Bayesian framework of predictive coding and devised a
model that casts endogenous perceptual transitions as a consequence of
prediction errors emerging from residual evidence for the suppressed percept.
Data simulations revealed close similarities between the model’s predictions
and key temporal characteristics of perceptual bistability, indicating that
the model was able to reproduce bistable perception. Fitting the predictive
coding model to behavioural data from an fMRI-experiment on bistable
perception, we found a correlation across participants between the model
parameter encoding perceptual stabilization and the behaviourally measured
frequency of perceptual transitions, corroborating that the model successfully
accounted for participants’ perception. Formal model comparison with
established models of bistable perception based on mutual inhibition and
adaptation, noise or a combination of adaptation and noise was used for the
validation of the predictive coding model against the established models. Most
importantly, model-based analyses of the fMRI data revealed that prediction
error time-courses derived from the predictive coding model correlated with
neural signal time-courses in bilateral inferior frontal gyri and anterior
insulae. Voxel-wise model selection indicated a superiority of the predictive
coding model over conventional analysis approaches in explaining neural
activity in these frontal areas, suggesting that frontal cortex encodes
prediction errors that mediate endogenous perceptual transitions in bistable
perception. Taken together, our current work provides a theoretical framework
that allows for the analysis of behavioural and neural data using a predictive
coding perspective on bistable perception. In this, our approach posits a
crucial role of prediction error signalling for the resolution of perceptual
ambiguities
Die Entstehung eindeutiger bewusster Wahrnehmung aus doppeldeutigen sensorischen Informationen
The research presented in this habilitation treatise seeks to understand the construction of unambiguous conscious experiences from ambiguous sensory information. Our work builds on the idea that the brain applies predictive processes to resolve the ambiguity inherent in sensory information. We developed a predictive coding algorithm that models the interaction of internal predictions with prediction errors driven by ambiguous sensory information. We combined model-based fMRI and TMS-induced virtual lesions to demonstrate that the processing of sensory ambiguity is not limited to feature-selective regions in sensory corteces, but involves supra-modal brain regions of the frontoparietal network. Our work proposes a key role for the inferior frontal cortex in regulating the access of conflicting information into conscious experience. Finally, we show that the interaction of internal predictions with external sensory information correlates with the severity of hallucinatory experiences in patients diagnosed with paranoid schizophrenia. In sum, the research presented in this habilitation treatise explains how the brain transforms ambiguous sensory data into unambiguous conscious experiences and suggests how alterations in this process may lead to hallucinations. Our computational and lesion-based approach advances the scientific understanding at two of the most important frontiers in contemporary neuroscience: the biology of consciousness and neurocomputational theories of psychosis
Perzeptuelle Wechsel bei bistabiler Wahrnehmung werden durch den Frontoparietalen Kortex mediiert
In bistable perception, ambiguous stimuli elicit spontaneous (endogenous)
transitions between two mutually exclusive percepts while sensory stimulation
remains constant. Such endogenous perceptual transitions have been studied in
comparison with stimulus-induced changes in perception generated in a so-
called “replay” condition. In the replay condition, perceptual transitions are
created by a disambiguated version of the stimulus and designed to be as
similar as possible to their ambiguous counterparts with respect to quality
and timing. In a number of studies using functional magnetic resonance imaging
(fMRI), the statistical comparison between endogenous and stimulus-induced
perceptual transitions has shown that significantly higher “Blood Oxygen Level
Dependent” (BOLD) responses in right hemispheric frontal and parietal brain
areas are associated with endogenous perceptual transitions. The functional
role of this frontoparietal network has remained controversial, however. On
the one hand, it has been argued that this enhanced activity might reflect
causal influences of regions in frontal and parietal cortex on the processing
in sensory brain areas and thus point to the importance of “top-down”
processes for bistable perception. On the other hand, it has been proposed
that differences in the BOLD signals measured might result from discrepancies
in the perceptual quality of transitions between the two conditions. This
“bottom–up” explanation focuses above all on possibly longer durations of
perceptual transitions in the bistable as compared to the replay condition,
being reflected by differences in frontoparietal activity. The goal of this
experiment was to disentangle these two hypotheses in a fMRI experiment on 15
healthy human participants. Using a rotating Lissajous figure, we elicited
endogenous and stimulus-induced changes in perception, whereby participants
rated the perceived duration of these events. Furthermore, we used
“Statistical Parametric Mapping” (SPM) to test the BOLD activity associated
with perceptual transitions in the bistable condition against the replay
condition. Finally, we applied “Dynamic Causal Modeling” (DCM) in order to
determine the neural model that most readily explains the observed BOLD signal
in terms of effective connectivity. We replicated previous findings of
enhanced activity in frontoparietal brain regions for endogeneous perceptual
transitions whilst controlling for potential confounds of differences in
transition duration between the two conditions. Our DCM results indicated that
enhanced activity for perceptual transitions during bistability is associated
with a modulation of “top-down” connectivity from frontal to visual cortex.
Taken together, these findings suggest that activity in frontoparietal brain
areas is crucially involved in perceptual transitions during bistable
perception in terms of “top–down” connectivity.Während bistabiler Wahrnehmung rufen ambige Stimuli bei konstanter
sensorischer Stimulation spontane (endogene) Wechsel zwischen zwei distinkten
Wahrnehmungsinhalten hervor. Eine Möglichkeit der Erforschung dieser
perzeptuellen Ereignisse besteht darin, endogene Wahrnehmungswechsel mit
Stimulus-induzierten Ă„nderungen der Wahrnehmungsinhalte zu vergleichen, welche
in einer sogenannten „Replay“ Bedingung erzeugt werden. Diese experimentelle
Bedingung versucht, durch eine disambiguierte Version des Stimulus die
perzeptuellen Eigenschaften von Wahrnehmungswechseln der bistabilen Bedingung
in Qualität und zeitlicher Abfolge möglichst genau nachzubilden. Der
statistische Vergleich zwischen den mit endogenen und Stimulus–induzierten
Wahrnehmungswechseln assoziierten „Blood Oxygen Level Dependent“ (BOLD)
Signalen der funktionellen Magnetresonanztomographie (fMRT) erbrachte in einer
Reihe von Studien eine signifikant höhere Aktivität in rechtshemisphärisch
lokalisierten frontalen und parietalen Gehirnarealen fĂĽr endogene perzeptuelle
Wechsel. Die funktionelle Bedeutung dieses frontoparietalen Netzwerks blieb
bislang jedoch umstritten. Einerseits wird angenommen, die erhöhte Aktivität
von Regionen im frontalen und parietalen Kortex spiegele deren kausale
Beteiligung an der Verarbeitung des ambigen Stimulus in sensorischen
Gehirnarealen wider und liefere damit einen Hinweis auf die Bedeutung von
„top–down“ Prozessen für die bistabile Wahrnehmung. Andererseits wird
argumentiert, eine solche frontoparietale Aktivität resultiere aus den
unterschiedlichen perzeptuellen Eigenschaften der Wahrnehmungswechsel in
beiden Bedingungen. Dieser „bottom–up“ Ansatz verwies insbesondere auf die im
Vergleich zur „Replay“ Bedingung möglicherweise längere zeitliche Ausdehnung
von Wahrnehmungswechseln in der bistabilen Bedingung, welche sich in einer
erhöhten frontoparietalen Aktivität niederschlagen könne. Das Ziel der
vorliegenden Untersuchung war es, diese beiden Hypothesen in einem fMRT
Experiment an 15 gesunden Probanden voneinander abzugrenzen. Hierzu haben wir
mit Hilfe einer rotierenden Lissajous–Figur spontane und Stimulus–induzierte
Wahrnehmungswechsel erzeugt und die zeitliche Ausdehnung dieser Ereignisse von
den Studienteilnehmern bewerten lassen. Des Weiteren haben wir die mit den
Wahrnehmungswechseln assoziierten BOLD Signale in beiden Bedingungen unter
Verwendung von „Statistical Parametric Mapping“ (SPM) gegeneinander getestet.
Schließen haben wir mit Hilfe von „Dynamic Causal Modeling“ (DCM) dasjenige
neuronale Modell identifiziert, welches den Zeitverlauf des BOLD Signales
während unseres Experiments im Sinne effektiver Konnektivität am besten
erklärt. Im Gegensatz zu früheren Studien konnten wir potentielle Störfaktoren
im Sinne einer unterschiedlichen zeitlichen Ausdehnung der Wahrnehmungswechsel
zwischen beiden Bedingungen ausschließen. Eine erhöhte frontoparietale
Aktivität für endogene Wahrnehmungswechsel konnten wir hingegen bestätigen.
Die Ergebnisse unserer DCM Analyse zeigten, dass die erhöhte BOLD Aktivität
für bistabile Wahrnehmungswechsel mit einer Modulation der Konnektivität vom
frontalen zum visuellen Kortex einhergeht. Zusammenfassend legen diese Befunde
nahe, dass die Aktivität in frontoparietalen Gehirnarealen im Sinne einer
„top–down“ Konnektivität entscheidend an perzeptuellen Wechseln der bistabilen
Wahrnehmung beteiligt ist
Bistable perception alternates between internal and external modes of sensory processing
Perceptual history can exert pronounced effects on the contents of conscious experience: when confronted with completely ambiguous stimuli, perception does not waver at random between diverging stimulus interpretations but sticks with recent percepts for prolonged intervals. Here, we investigated the relevance of perceptual history in situations more similar to everyday experience, where sensory stimuli are usually not completely ambiguous. Using partially ambiguous visual stimuli, we found that the balance between past and present is not stable over time but slowly fluctuates between two opposing modes. For time periods of up to several minutes, perception was either largely determined by perceptual history or driven predominantly by disambiguating sensory evidence. Computational modeling suggested that the construction of unambiguous conscious experiences is modulated by slow fluctuations between internally and externally oriented modes of sensory processing
Perceptual stability of the Lissajous figure is modulated by the speed of illusory rotation (Weilnhammer et al. 2016)
This fileset contains the raw Matlab data files (*.mat) and the corresponding Matlab script (*.m) for the analysis. It also contains data (*.csv) which were submitted to the rm-ANOVA.<br
Perceptual Stability of the Lissajous Figure Is Modulated by the Speed of Illusory Rotation.
Lissajous figures represent ambiguous structure-from-motion stimuli rotating in depth and have proven to be a versatile tool to explore the cognitive and neural mechanisms underlying bistable perception. They are generated by the intersection of two sinusoids with perpendicular axes and increasing phase-shift whose frequency determines the speed of illusory 3D rotation. Recently, we found that Lissajous figures of higher shifting frequencies elicited longer perceptual phase durations and tentatively proposed a "representational momentum" account. In this study, our aim was twofold. First, we aimed to gather more behavioral evidence related to the perceptual dynamics of the Lissajous figure by simultaneously varying its shifting frequency and size. Using a conventional analysis, we investigated the effects of our experimental manipulations on transition probability (i.e., the probability that the current percept will change at the next critical stimulus configuration). Second, we sought to test the impact of our experimental factors on the occurrence of transitions in bistable perception by means of a Bayesian approach that can be used to directly quantify the impact of contextual cues on perceptual stability. We thereby estimated the implicit prediction of perceptual stability and how it is modulated by experimental manipulations
Correction: Psychotic Experiences and Overhasty Inferences Are Related to Maladaptive Learning.
[This corrects the article DOI: 10.1371/journal.pcbi.1005328.]
Lissajous figure and distribution of perceptual phase durations.
<p>(A) Lissajous are generated by the intersection of two sinusoids with perpendicular axes and increasing phase-shift whose frequency determines the speed of illusory 3D rotation. Following their introduction to experimental psychology, Lissajous figures were originally studied by means of twin-oscillators and analog cathode ray oscillographs in the 1940s and 1950s [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0160772#pone.0160772.ref006" target="_blank">6</a>]. (B) Perceptual phase duration across all participants, runs and conditions. Distributions with a sharp rise and a long tail are typical of bistable perception.</p