167 research outputs found
Can synchronization explain representational content? : A reply to Caspar M. Schwiedrzik
Multivariate decoding provides an important tool for studying the representation and transformation of mental contents in the human brain. Specifically, decoding can be used to identify the neural correlates of contents of consciousness (NCCCs). Decoding of functional magnetic resonance imaging (fMRI) signals has so far mostly revealed content-selectivity in sensory brain regions, but not in prefrontal cortex. The limitations of fMRI-decoding only permit cautious conclusions because fMRI signals are only indirectly related to neural coding. However, the role of prefrontal cortex in visual awareness is also questioned by other findings, reviewed in Schwiedrzik (this collection). Neural synchronization might offer an alternative to solving the binding problem by providing a computational means of integrating information encoded in distributed brain regions. However, it is unclear whether synchronization in itself serves as a coding dimension for visual features. Furthermore, other alternatives to synchronization, especially the role of spatial codes, need to be considered as potential solutions to the feature binding problem
An information-based approach to consciousness : mental state decoding
The debate on the neural correlates of visual consciousness often focuses on the question of which additional processing has to happen for a visual representation to enter consciousness. However, a related question that has only rarely been addressed is which brain regions directly encodespecific contents of consciousness. The search for these core neural correlates of contents of consciousness (NCCCs) requires establishing a mapping between sensory experiences and population measures of brain activity in specific brain regions. One approach for establishing this mapping is multivariate decoding. Using this technique, several properties of NCCCs have been investigated. Masking studies have revealed that information about sensory stimuli can be decoded from the primary visual cortex, even if the stimuli cannot be consciously identified by a subject. This suggests that information that does not reach awareness can be encapsulated in early visual stages of processing. Visual imagery representations and veridical perception share similar neural representations in higher-level visual regions, suggesting that these regions are directly related to the encoding of conscious visual experience. But population signals in these higher-level visual regions cannot be the sole carriers of visual experiences because they are invariant to low-level visual features. We found no evidence for increased encoding of sensory information in the prefrontal cortex when a stimulus reaches awareness. In general, we found no role of the prefrontal cortex in encoding sensory experiences at all. However, the improved discrimination of sensory information during perceptual learning could be explained by an improved read-out by the prefrontal cortex. One possible implication is that prefrontal cortical regions do not participate in the encoding of sensory features per se. Instead they may be relevant in making decisions about sensory features, without exhibiting a re-representation of sensory information
Neural Correlates of Conscious Perception. The Role of Primary Visual Cortex in Visual Awareness.
This study investigates which neural populations represent low-level dimensions of conscious perception. First, a general framework is presented that will allow the separation of different aspects of visual awareness. A set of six criteria is developed that allows one to assess whether a neural population could in principle represent a dimension of conscious perception. These criteria are then applied to previous studies on the neurophysiology and neuropsychology of conscious perception. In the following empirical section a study on the relationship between perceived contrast and activity in primary visual cortex is performed using a combination of EEG, MEG and psychophysics. Lateral masking was used to dissociate the physical and the perceived contrast of a target grating. Transient potentials and magnetic fields evoked by the flashed target gratings were recorded and compared to psychophysical judgements of perceived contrast. At all investigated contrast levels, the amplitudes of electrophysiological transients correlated better with perceived than with physical target contrast. This held especially for the late transient. Source localisation indicated that the transients in question are likely to originate in primary visual cortex. The study presented here is the first ever to study perceptual constancy by recording psychophysics and physiological responses synchronously. The results identify the activity of primary visual cortex as the most likely neural basis of perceived contrast
Free will beliefs are better predicted by dualism than determinism beliefs across different cultures
Most people believe in free will. Whether this belief is warranted or not, free will beliefs
(FWB) are foundational for many legal systems and reducing FWB has effects on behavior
from the motor to the social level. This raises the important question as to which specific
FWB people hold. There are many different ways to conceptualize free will, and some might
see physical determinism as a threat that might reduce FWB, while others might not. Here,
we investigate lay FWB in a large, representative, replicated online survey study in the US
and Singapore (n = 1800), assessing differences in FWB with unprecedented depth within
and between cultures. Specifically, we assess the relation of FWB, as measured using the
Free Will Inventory, to determinism, dualism and related concepts like libertarianism and
compatibilism. We find that libertarian, compatibilist, and dualist, intuitions were related to
FWB, but that these intuitions were often logically inconsistent. Importantly, direct comparisons
suggest that dualism was more predictive of FWB than other intuitions. Thus, believing
in free will goes hand-in-hand with a belief in a non-physical mind. Highlighting the importance
of dualism for FWB impacts academic debates on free will, which currently largely
focus on its relation to determinism. Our findings also shed light on how recent (neuro)scientific
findings might impact FWB. Demonstrating physical determinism in the brain need not
have a strong impact on FWB, due to a wide-spread belief in dualism
The Decoding Toolbox (TDT): a versatile software package for multivariate analyses of functional imaging data
The multivariate analysis of brain signals has recently sparked a great amount of interest, yet accessible and versatile tools to carry out decoding analyses are scarce. Here we introduce The Decoding Toolbox (TDT) which represents a user-friendly, powerful and flexible package for multivariate analysis of functional brain imaging data. TDT is written in Matlab and equipped with an interface to the widely used brain data analysis package SPM. The toolbox allows running fast whole-brain analyses, region-of-interest analyses and searchlight analyses, using machine learning classifiers, pattern correlation analysis, or representational similarity analysis. It offers automatic creation and visualization of diverse cross-validation schemes, feature scaling, nested parameter selection, a variety of feature selection methods, multiclass capabilities, and pattern reconstruction from classifier weights. While basic users can implement a generic analysis in one line of code, advanced users can extend the toolbox to their needs or exploit the structure to combine it with external high-performance classification toolboxes. The toolbox comes with an example data set which can be used to try out the various analysis methods. Taken together, TDT offers a promising option for researchers who want to employ multivariate analyses of brain activity patterns.DFG, GRK 1589, Verarbeitung sensorischer Informationen in neuronalen SystemenBMBF, 01GQ1006, Modulation von Bewertungsprozessen beim menschlichen Entscheidungsverhalten: ein neurocomputationaler Ansat
Neocortical substrates of feelings evoked with music in the ACC, insula, and somatosensory cortex
Neurobiological models of emotion focus traditionally on limbic/paralimbic regions as neural substrates of emotion generation, and insular cortex (in conjunction with isocortical anterior cingulate cortex, ACC) as the neural substrate of feelings. An emerging view, however, highlights the importance of isocortical regions beyond insula and ACC for the subjective feeling of emotions. We used music to evoke feelings of joy and fear, and multivariate pattern analysis (MVPA) to decode representations of feeling states in functional magnetic resonance (fMRI) data of n = 24 participants. Most of the brain regions providing information about feeling representations were neocortical regions. These included, in addition to granular insula and cingulate cortex, primary and secondary somatosensory cortex, premotor cortex, frontal operculum, and auditory cortex. The multivoxel activity patterns corresponding to feeling representations emerged within a few seconds, gained in strength with increasing stimulus duration, and replicated results of a hypothesis-generating decoding analysis from an independent experiment. Our results indicate that several neocortical regions (including insula, cingulate, somatosensory and premotor cortices) are important for the generation and modulation of feeling states. We propose that secondary somatosensory cortex, which covers the parietal operculum and encroaches on the posterior insula, is of particular importance for the encoding of emotion percepts, i.e., preverbal representations of subjective feeling.publishedVersio
Switch-independent task representations in frontal and parietal cortex
Alternating between two tasks is effortful and impairs performance. Previous fMRI studies have found increased activity in frontoparietal cortex when task switching is required. One possibility is that the additional control demands for switch trials are met by strengthening task representations in the human brain. Alternatively, on switch trials, the residual representation of the previous task might impede the buildup of a neural task representation. This would predict weaker task representations on switch trials, thus also explaining the performance costs. To test this, male and female participants were cued to perform one of two similar tasks, with the task being repeated or switched between successive trials. Multivoxel pattern analysis was used to test which regions encode the tasks and whether this encoding differs between switch and repeat trials. As expected, we found information about task representations in frontal and parietal cortex, but there was no difference in the decoding accuracy of task-related information between switch and repeat trials. Using cross-classification, we found that the frontoparietal cortex encodes tasks using a generalizable spatial pattern in switch and repeat trials. Therefore, task representations in frontal and parietal cortex are largely switch independent. We found no evidence that neural information about task representations in these regions can explain behavioral costs usually associated with task switching
Encoding of continuous perceptual choices in human early visual cortex
IntroductionResearch on the neural mechanisms of perceptual decision-making has typically focused on simple categorical choices, say between two alternative motion directions. Studies on such discrete alternatives have often suggested that choices are encoded either in a motor-based or in an abstract, categorical format in regions beyond sensory cortex.MethodsIn this study, we used motion stimuli that could vary anywhere between 0° and 360° to assess how the brain encodes choices for features that span the full sensory continuum. We employed a combination of neuroimaging and encoding models based on Gaussian process regression to assess how either stimuli or choices were encoded in brain responses.ResultsWe found that single-voxel tuning patterns could be used to reconstruct the trial-by-trial physical direction of motion as well as the participants’ continuous choices. Importantly, these continuous choice signals were primarily observed in early visual areas. The tuning properties in this region generalized between choice encoding and stimulus encoding, even for reports that reflected pure guessing.DiscussionWe found only little information related to the decision outcome in regions beyond visual cortex, such as parietal cortex, possibly because our task did not involve differential motor preparation. This could suggest that decisions for continuous stimuli take can place already in sensory brain regions, potentially using similar mechanisms to the sensory recruitment in visual working memory
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