Publications by authors named "Michael H Herzog"

188 Publications

Serial dependence does not originate from low-level visual processing.

Cognition 2021 Apr 7;212:104709. Epub 2021 Apr 7.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Perception depends not only on the current sensory input but also on the preceding history of stimuli. In serial dependence (SD), for example, the orientation of a Gabor patch is mistakenly reported as more similar to previous trials than it actually is. This bias is typically observed for moderate orientation differences (<45°) and extends over a few trials in the past. It is hotly debated whether SD originates at perceptual or post-perceptual, e.g., decisional, stages. Here, we provide evidence for the latter hypothesis. We presented Gabor patches with different spatial frequencies or Gabors intermingled with dot patterns. Even though stimuli were perceptually clearly dissimilar, we found robust SD effects arguing against any perceptual account. These findings suggest a re-evaluation of current models and theoretical accounts of SD.
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http://dx.doi.org/10.1016/j.cognition.2021.104709DOI Listing
April 2021

Response to commentaries on 'hard criteria for empirical theories of consciousness'.

Cogn Neurosci 2021 Jan-Jan;12(2):99-101. Epub 2020 Nov 29.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale De Lausanne (EPFL), Lausanne, Switzerland.

In consciousness research, we have a very large number of theories, which exceeds by far the number of theories in other fields. We recently presented a set of criteria for evaluating and comparing theories of consciousness, and then applied the criteria to a number of different theories. Our publication sparked strong responses as evident by the many comments published in (this issue). Overall, there seems to be consensus that a theory of consciousness (ToC) needs to have an unconscious alternative, but other criteria sparked controversy. The hottest debate is to what extent consciousness needs to work with purely 1 person data, containing information not available in 3 person reports. We would like to thank all the commentators for their lively input and we look forward to continued dialog as theories evolve and compete.
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http://dx.doi.org/10.1080/17588928.2020.1853086DOI Listing
November 2020

Electrophysiological correlates of visual backward masking in patients with bipolar disorder.

Psychiatry Res Neuroimaging 2021 01 14;307:111206. Epub 2020 Oct 14.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.

In visual backward masking (VBM), a target is followed by a mask that decreases target discriminability. Schizophrenia patients (SZ) show strong and reproducible masking impairments, which are associated with reduced EEG amplitudes. Patients with bipolar disorder (BP) show masking deficits, too. Here, we investigated the neural EEG correlates of VBM in BP. 122 SZ, 94 unaffected controls, and 38 BP joined a standard VBM experiment. 123 SZ, 94 unaffected controls and 16 BP joined a corresponding EEG experiment, analyzed in terms of global field power. As in previous studies, SZ and BP show strong masking deficits. Importantly and similarly to SZ, BP show decreased global field power amplitudes at approximately 200 ms after the target onset, compared to controls. These results suggest that VBM deficits are not specific for schizophrenia but for a broader range of functional psychoses. Potentially, both SZ and BP show deficient target enhancement.
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http://dx.doi.org/10.1016/j.pscychresns.2020.111206DOI Listing
January 2021

All in Good Time: Long-Lasting Postdictive Effects Reveal Discrete Perception.

Trends Cogn Sci 2020 10 3;24(10):826-837. Epub 2020 Sep 3.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Is consciousness a continuous stream of percepts or is it discrete, occurring only at certain moments in time? This question has puzzled philosophers, psychologists, and neuroscientists for centuries. Both hypotheses have fallen repeatedly in and out of favor. Here, we review recent studies exploring long-lasting postdictive effects and show that the results favor a two-stage discrete model, in which substantial periods of continuous unconscious processing precede discrete conscious percepts. We propose that such a model marries the advantages of both continuous and discrete models and resolves centuries old debates about perception and consciousness.
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http://dx.doi.org/10.1016/j.tics.2020.07.001DOI Listing
October 2020

When illusions merge.

J Vis 2020 08;20(8):12

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

We recently found only weak correlations between the susceptibility to various visual illusions. However, we observed strong correlations among different variants of an illusion, suggesting that the visual space of illusions includes several illusion-specific factors. Here, we specifically examined how factors for the vertical-horizontal, Müller-Lyer, and Ponzo illusions relate to each other. We measured the susceptibility to each illusion separately and to combinations of two illusions, which we refer to as a merged illusion; for example, we tested the Müller-Lyer illusion and the vertical-horizontal illusion, as well as a merged version of both illusions. We used an adjustment procedure in two experiments with 306 and 98 participants, respectively. Using path analyses, correlations, and exploratory factor analyses, we found that the susceptibility to a merged illusion is well predicted from the susceptibilities to the individual illusions. We suggest that there are illusion-specific factors that, by independent combinations, represent the whole visual structure underlying illusions.
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http://dx.doi.org/10.1167/jov.20.8.12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7438631PMC
August 2020

Perceptual grouping leads to objecthood effects in the Ebbinghaus illusion.

J Vis 2020 08;20(8):11

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.

The Ebbinghaus illusion is argued to be a product of low-level contour interactions or a higher cognitive comparison process. We examined the effect of grouping on the illusion by manipulating objecthood, i.e., the degree to which an object is a cohesive perceptual entity. We hypothesized that reduced objecthood would decrease the illusion magnitude, because the objects become less efficient in the comparison process. To test this hypothesis, we used a version of the illusion where the target and flanking objects were squares that were composed from their corners or sides. Degree of objecthood was manipulated by changing the gap size or rotation angle of the elements constructing the objects, so that larger gaps and angles produced less cohesive objects than smaller. Participants performed an adjustment procedure on the test target to match a control target in size. In addition, subjective reports of the objects' shape were collected as a measure of perceived shape. Our results show decreased illusion magnitude with increasing gap size and rotation angle. Surprisingly, the perceived shape of the objects did not correlate with illusion magnitude. These results provide novel evidence of the role of mid-level processes in the Ebbinghaus illusion and point to a dissociation between subjective and objective measures of objecthood.
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http://dx.doi.org/10.1167/jov.20.8.11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7438686PMC
August 2020

Object identity determines trans-saccadic integration.

J Vis 2020 07;20(7):33

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Humans make two to four rapid eye movements (saccades) per second, which, surprisingly, does not lead to abrupt changes in vision. To the contrary, we perceive a stable world. Hence, an important question is how information is integrated across saccades. To investigate this question, we used the sequential metacontrast paradigm (SQM), where two expanding streams of lines are presented. When one line is spatially offset, the other lines are perceived as being offset, too. When more lines are offset, all offsets integrate mandatorily; that is, observers cannot report the individual offsets but perceive one integrated offset. Here, we asked observers to make a saccade during the SQM. Even though the saccades caused a highly disrupted motion trajectory on the retina, offsets presented before and after the saccade integrated mandatorily. When observers made no saccade and the streams were displaced on the screen so that a similarly disrupted retinal image occurred as in the previous condition, no integration occurred. We suggest that trans-saccadic integration and perception are determined by object identity in spatiotopic coordinates and not by the retinal image.
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http://dx.doi.org/10.1167/jov.20.7.33DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7424110PMC
July 2020

Capsule networks as recurrent models of grouping and segmentation.

PLoS Comput Biol 2020 07 21;16(7):e1008017. Epub 2020 Jul 21.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Classically, visual processing is described as a cascade of local feedforward computations. Feedforward Convolutional Neural Networks (ffCNNs) have shown how powerful such models can be. However, using visual crowding as a well-controlled challenge, we previously showed that no classic model of vision, including ffCNNs, can explain human global shape processing. Here, we show that Capsule Neural Networks (CapsNets), combining ffCNNs with recurrent grouping and segmentation, solve this challenge. We also show that ffCNNs and standard recurrent CNNs do not, suggesting that the grouping and segmentation capabilities of CapsNets are crucial. Furthermore, we provide psychophysical evidence that grouping and segmentation are implemented recurrently in humans, and show that CapsNets reproduce these results well. We discuss why recurrence seems needed to implement grouping and segmentation efficiently. Together, we provide mutually reinforcing psychophysical and computational evidence that a recurrent grouping and segmentation process is essential to understand the visual system and create better models that harness global shape computations.
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http://dx.doi.org/10.1371/journal.pcbi.1008017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7394447PMC
July 2020

Hard criteria for empirical theories of consciousness.

Cogn Neurosci 2021 Jan-Jan;12(2):41-62. Epub 2020 Jul 14.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale De Lausanne (EPFL), Lausanne, Switzerland.

Consciousness is now a well-established field of empirical research. A large body of experimental results has been accumulated and is steadily growing. In parallel, many Theories of Consciousness (ToCs) have been proposed. These theories are diverse in nature, ranging from computational to neurophysiological and quantum theoretical approaches. This contrasts with other fields of natural science, which host a smaller number of competing theories. We suggest that one reason for this abundance of extremely different theories may be the lack of stringent criteria specifying how empirical data constrains ToCs. First, we argue that consciousness is a well-defined topic from an empirical point of view and motivate a purely empirical stance on the quest for consciousness. Second, we present a checklist of criteria that, we propose, empirical ToCs need to cope with. Third, we review 13 of the most influential ToCs and subject them to the criteria. Our analysis helps to situate these different ToCs in the theoretical landscapeand sheds light on their strengths and weaknesses from a strictly empirical point of view.
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http://dx.doi.org/10.1080/17588928.2020.1772214DOI Listing
July 2020

EEG microstates are a candidate endophenotype for schizophrenia.

Nat Commun 2020 06 18;11(1):3089. Epub 2020 Jun 18.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Electroencephalogram microstates are recurrent scalp potential configurations that remain stable for around 90 ms. The dynamics of two of the four canonical classes of microstates, commonly labeled as C and D, have been suggested as a potential endophenotype for schizophrenia. For endophenotypes, unaffected relatives of patients must show abnormalities compared to controls. Here, we examined microstate dynamics in resting-state recordings of unaffected siblings of patients with schizophrenia, patients with schizophrenia, healthy controls, and patients with first episodes of psychosis (FEP). Patients with schizophrenia and their siblings showed increased presence of microstate class C and decreased presence of microstate class D compared to controls. No difference was found between FEP and chronic patients. Our findings suggest that the dynamics of microstate classes C and D are a candidate endophenotype for schizophrenia.
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http://dx.doi.org/10.1038/s41467-020-16914-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303216PMC
June 2020

Individual differences in the Müller-Lyer and Ponzo illusions are stable across different contexts.

J Vis 2020 06;20(6)

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Vision scientists have attempted to classify visual illusions according to certain aspects, such as brightness or spatial features. For example, Piaget proposed that visual illusion magnitudes either decrease or increase with age. Subsequently, it was suggested that illusions are segregated according to their context: real-world contexts enhance and abstract contexts inhibit illusion magnitudes with age. We tested the effects of context on the Müller-Lyer and Ponzo illusions with a standard condition (no additional context), a line-drawing perspective condition, and a real-world perspective condition. A mixed-effects model analysis, based on data from 76 observers with ages ranging from 6 to 66 years, did not reveal any significant interaction between context and age. Although we found strong intra-illusion correlations for both illusions, we found only weak inter-illusion correlations, suggesting that the structure underlying these two spatial illusions includes several specific factors.
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http://dx.doi.org/10.1167/jov.20.6.4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7416885PMC
June 2020

Non-retinotopic adaptive center-surround modulation in motion processing.

Vision Res 2020 09 4;174:10-21. Epub 2020 Jun 4.

Perceptual and Cognitive Dynamics Laboratory, Department of Electrical & Computer Engineering, University of Denver, Denver, CO 80208, USA. Electronic address:

The early visual system is organized retinotopically. However, under ecological viewing conditions, motion perception occurs in non-retinotopic coordinates. Even though many studies revealed the central role of non-retinotopic processes, very little is known about their mechanisms and neural correlates. Tadin and colleagues found that increasing the spatial size of a high-contrast drifting-Gabor deteriorates motion-direction discrimination, whereas the opposite occurs with a low-contrast stimulus. The results were proposed to reflect an adaptive center-surround antagonism, whereby at low-contrast the excitatory center dominates whereas at high-contrast suppressive-surround mechanisms become more effective. Because ecological vision is non-retinotopic, we tested the hypothesis that the non-retinotopic system also processes motion information by means of an adaptive center-surround mechanism. We used the Ternus-Pikler display designed to provide either a retinotopic or a non-retinotopic reference-frame. Our results suggest that the non-retinotopic processes underlying motion perception are also mediated by an adaptive center-surround mechanism.
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http://dx.doi.org/10.1016/j.visres.2020.05.007DOI Listing
September 2020

Bayesian regression explains how human participants handle parameter uncertainty.

PLoS Comput Biol 2020 05 18;16(5):e1007886. Epub 2020 May 18.

Department of Physiology, University of Bern, Bern, Switzerland.

Accumulating evidence indicates that the human brain copes with sensory uncertainty in accordance with Bayes' rule. However, it is unknown how humans make predictions when the generative model of the task at hand is described by uncertain parameters. Here, we tested whether and how humans take parameter uncertainty into account in a regression task. Participants extrapolated a parabola from a limited number of noisy points, shown on a computer screen. The quadratic parameter was drawn from a bimodal prior distribution. We tested whether human observers take full advantage of the given information, including the likelihood of the quadratic parameter value given the observed points and the quadratic parameter's prior distribution. We compared human performance with Bayesian regression, which is the (Bayes) optimal solution to this problem, and three sub-optimal models, which are simpler to compute. Our results show that, under our specific experimental conditions, humans behave in a way that is consistent with Bayesian regression. Moreover, our results support the hypothesis that humans generate responses in a manner consistent with probability matching rather than Bayesian decision theory.
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http://dx.doi.org/10.1371/journal.pcbi.1007886DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7259793PMC
May 2020

Risk prediction error signaling: A two-component response?

Neuroimage 2020 07 2;214:116766. Epub 2020 Apr 2.

Geneva Finance Research Institute and Center for Affective Sciences, University of Geneva, Switzerland. Electronic address:

Organisms use rewards to navigate and adapt to (uncertain) environments. Error-based learning about rewards is supported by the dopaminergic system, which is thought to signal reward prediction errors to make adjustments to past predictions. More recently, the phasic dopamine response was suggested to have two components: the first rapid component is thought to signal the detection of a potentially rewarding stimulus; the second, slightly later component characterizes the stimulus by its reward prediction error. Error-based learning signals have also been found for risk. However, whether the neural generators of these signals employ a two-component coding scheme like the dopaminergic system is unknown. Here, using human high density EEG, we ask whether risk learning, or more generally speaking surprise-based learning under uncertainty, is similarly comprised of two temporally dissociable components. Using a simple card game, we show that the risk prediction error is reflected in the amplitude of the P3b component. This P3b modulation is preceded by an earlier component, that is modulated by the stimulus salience. Source analyses are compatible with the idea that both the early salience signal and the later risk prediction error signal are generated in insular, frontal, and temporal cortex. The identified sources are parts of the risk processing network that receives input from noradrenergic cells in the locus coeruleus. Finally, the P3b amplitude modulation is mirrored by an analogous modulation of pupil size, which is consistent with the idea that both the P3b and pupil size indirectly reflect locus coeruleus activity.
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http://dx.doi.org/10.1016/j.neuroimage.2020.116766DOI Listing
July 2020

How stable is perception in #TheDress and #TheShoe?

Vision Res 2020 04 18;169:1-5. Epub 2020 Feb 18.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.

#TheDress is perceived by some people as black and blue while others perceive it as white and gold. We have previously shown that the first encounter with #TheDress strongly biases its perception. This percept remained stable during the experiment, suggesting a role of one-shot learning. #TheShoe is another image that elicits similar bimodal color percepts. Here, we investigated how percepts change over time in both #TheShoe and #TheDress. First, we show that the important role of one-shot learning, which we found for #TheDress extends to #TheShoe. Similarly to our previous results with the dress, hiding large parts of the image with occluders biased the percept of the shoe. The percept did not change for the majority of observers when the occluders were removed. Second, we investigated if and how percepts switch over a time course of 14 days. We found that although some observers experienced percept switches, the percept was largely stable for most observers.
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http://dx.doi.org/10.1016/j.visres.2020.01.007DOI Listing
April 2020

Neural Compensation Mechanisms of Siblings of Schizophrenia Patients as Revealed by High-Density EEG.

Schizophr Bull 2020 07;46(4):1009-1018

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Visual backward masking (VBM) deficits are candidate endophenotypes of schizophrenia indexing genetic liability of the disorder. In VBM, a target is followed by a mask that deteriorates target perception. Schizophrenia patients and, to a lesser extent, their unaffected relatives show strong and reproducible VBM deficits. In patients, VBM deficits are associated with strongly decreased amplitudes in the evoked-related potentials (ERPs). Here, to unveil the neural mechanisms of VBM in schizophrenia, circumventing illness-specific confounds, we investigated the electroencephalogram correlates of VBM in unaffected siblings of schizophrenia patients. We tested 110 schizophrenia patients, 60 siblings, and 83 healthy controls. As in previous studies, patients showed strong behavioral deficits and decreased ERP amplitudes compared to controls. Surprisingly, the ERP amplitudes of siblings were even higher than the ones of controls, while their performances were similar. ERP amplitudes in siblings were found to correlate with performance. These results suggest that VBM is deteriorated in patients and siblings. However, siblings, unlike patients, can partially compensate for the deficits by over-activating a network of brain regions.
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http://dx.doi.org/10.1093/schbul/sbz133DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7345810PMC
July 2020

Factors underlying visual illusions are illusion-specific but not feature-specific.

J Vis 2019 12;19(14):12

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Common factors are ubiquitous. For example, there is a common factor, g, for intelligence. In vision, there is much weaker evidence for such common factors. For example, visual illusion magnitudes correlate only weakly with each other. Here, we investigated whether illusions are hyper-specific as in perceptual learning. First, we tested 19 variants of the Ebbinghaus illusion that differed in color, shape, or texture. Correlations between the illusion magnitudes of the different variants were mostly significant. Second, we reanalyzed a dataset from a previous experiment where 10 illusions were tested under four conditions of luminance and found significant correlations between the different luminance conditions of each illusion. However, there were only very weak correlations between the 10 different illusions. Third, five visual illusions were tested with four orientations. Again, there were significant correlations between the four orientations of each illusion, but not across different illusions. The weak inter-illusion correlations suggest that there is no unique common mechanism for the tested illusions. We suggest that most illusions make up their own factor.
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http://dx.doi.org/10.1167/19.14.12DOI Listing
December 2019

One-shot learning and behavioral eligibility traces in sequential decision making.

Elife 2019 11 11;8. Epub 2019 Nov 11.

Swiss Center for Affective Sciences, University of Geneva, Geneva, Switzerland.

In many daily tasks, we make multiple decisions before reaching a goal. In order to learn such sequences of decisions, a mechanism to link earlier actions to later reward is necessary. Reinforcement learning (RL) theory suggests two classes of algorithms solving this credit assignment problem: In classic temporal-difference learning, earlier actions receive reward information only after multiple repetitions of the task, whereas models with eligibility traces reinforce entire sequences of actions from a single experience (one-shot). Here, we show one-shot learning of sequences. We developed a novel paradigm to observe which actions and states along a multi-step sequence are reinforced after a single reward. By focusing our analysis on those states for which RL with and without eligibility trace make qualitatively distinct predictions, we find direct behavioral (choice probability) and physiological (pupil dilation) signatures of reinforcement learning with eligibility trace across multiple sensory modalities.
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http://dx.doi.org/10.7554/eLife.47463DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6897511PMC
November 2019

Electrophysiological correlates of visual backward masking in patients with major depressive disorder.

Psychiatry Res Neuroimaging 2019 12 28;294:111004. Epub 2019 Oct 28.

Institute of Cognitive Neurosciences, Agricultural University of Georgia, Tbilisi, Georgia; Department of Psychiatry, Tbilisi State Medical University, Tbilisi, Georgia.

Depression and schizophrenia are two psychiatric diseases with high co-morbidity. For this reason, it is important to find sensitive endophenotypes, which may disentangle the two disorders. The Shine-Through paradigm, a visual backward masking task, is a potential endophenotype for schizophrenia. Masking is strongly deteriorated in schizophrenia patients, which is reflected in reduced EEG amplitudes. Here, we tested whether masking deficits and associated EEG changes are also found in patients with major depressive disorder. First, we replicated previous findings showing that depressive patients exhibit, at most, only weak masking deficits. Second, we found that the EEG amplitudes of depressive patients were reduced compared to controls and slightly increased compared to schizophrenia patients. As a secondary analysis, we compared the performance in the masking paradigm with three cognitive tasks, namely: the Wisconsin card sorting test, a verbal fluency test and a degraded continuous performance test. Performance in all but the verbal fluency test could discriminate schizophrenia from depression.
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http://dx.doi.org/10.1016/j.pscychresns.2019.111004DOI Listing
December 2019

Feature integration within discrete time windows.

Nat Commun 2019 10 25;10(1):4901. Epub 2019 Oct 25.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), EPFL SV BMI LPSY, Station 19 CH-1015, Lausanne, Switzerland.

Sensory information must be integrated over time to perceive, for example, motion and melodies. Here, to study temporal integration, we used the sequential metacontrast paradigm in which two expanding streams of lines are presented. When a line in one stream is offset observers perceive all other lines to be offset too, even though they are straight. When more lines are offset the offsets integrate mandatorily, i.e., observers cannot report the individual offsets. We show that mandatory integration lasts for up to 450 ms, depending on the observer. Importantly, integration occurs only when offsets are presented within a discrete window of time. Even stimuli that are in close spatio-temporal proximity do not integrate if they are in different windows. A window of integration starts with stimulus onset and integration in the next window has similar characteristics. We present a two-stage computational model based on discrete time windows that captures these effects.
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http://dx.doi.org/10.1038/s41467-019-12919-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6814726PMC
October 2019

Reference-frames in vision: Contributions of attentional tracking to nonretinotopic perception in the Ternus-Pikler display.

J Vis 2019 10;19(12)

Faculté de Psychologie et des Sciences de l'Éducation, Université de Genève, Geneva, Switzerland.

Perception depends on reference frames. For example, the "true" cycloidal motion trajectory of a reflector on a bike's wheel is invisible because we perceive the reflector motion relative to the bike's motion trajectory, which serves as a reference frame. To understand such an object-based motion perception, we suggested a "two-stage" model in which first reference frames are computed based on perceptual grouping (bike) and then features are attributed (reflector motion) based on group membership. The overarching goal of this study was to investigate how multiple features (i.e., motion, shape, and color) interact with attention to determine retinotopic or nonretinotopic reference frames. We found that, whereas tracking by focal attention can generate nonretinotopic reference-frames, the effect is rather small compared with motion-based grouping. Combined, our results support the two-stage model and clarify how various features and cues can work in conjunction or in competition to determine prevailing groups. These groups in turn establish reference frames according to which features are processed and bound together.
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http://dx.doi.org/10.1167/19.12.7DOI Listing
October 2019

Associations between genetic variations and global motion perception.

Exp Brain Res 2019 Oct 20;237(10):2729-2734. Epub 2019 Aug 20.

Laboratory of Psychophysics, Brain Mind Institute, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland.

The cholinergic system is known to strongly modulate perceptual and cognitive processes, and the alpha7 subunit of the cholinergic nicotinic receptor (CHRNA7) is broadly expressed within the visual system. Here, we assessed whether genetic variations of CHRNA7 affect coherent motion perception. Motion perception has been shown to decline with age, and it has previously been suggested that the effects of genetic variations are magnified by age. Therefore, we tested both older (n = 62) and younger adults (n = 63). We found that motion coherence thresholds were significantly higher for older compared to younger adults, which is in accordance with previous studies. Interestingly, there was a strong relationship between variants of the SNP rs2337980 of the CHRNA7 and motion direction discrimination. In particular, participants carrying the TC genotype had considerably lower motion coherence thresholds than CC carriers. The effect of genotype did not interact with age. Our results show that genetic variations are associated with perceptual performance, but are unlikely to explain age-related changes.
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http://dx.doi.org/10.1007/s00221-019-05627-7DOI Listing
October 2019

Exploring the Extent in the Visual Field of the Honeycomb and Extinction Illusions.

Iperception 2019 Jul-Aug;10(4):2041669519854784. Epub 2019 Jul 4.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.

There are situations in which what is perceived in central vision is different to what is perceived in the periphery, even though the stimulus display is uniform. Here, we studied two cases, known as the Extinction illusion and the Honeycomb illusion, involving small disks and lines, respectively, presented over a large extent of the visual field. Disks and lines are visible in the periphery on their own, but they become invisible when they are presented as part of a pattern (grid). Observers ( = 56) adjusted a circular probe to report the size of the region in which they had seen the lines or the disks. Different images had black or white lines/disks, and we included control stimuli in which these features were spatially separated from the regular grid of squares. We confirmed that the illusion was experienced by the majority of observers and is dependent on the interaction between the elements (i.e., the lines/disks have to be near the squares). We found a dissociation between the two illusions in the dependence on contrast polarity suggesting different mechanisms. We analysed the variability between individuals with respect to schizotypical and autistic-spectrum traits (short version of the Oxford-Liverpool Inventory of Feelings and Experiences [O-LIFE] questionnaire and the Autistic Quotient, respectively) but found no significant relationships. We discuss how illusions relative to what observers are aware of in the periphery may offer a unique tool to study visual awareness.
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http://dx.doi.org/10.1177/2041669519854784DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6611042PMC
July 2019

Dopaminergic modulation of motor network compensatory mechanisms in Parkinson's disease.

Hum Brain Mapp 2019 10 10;40(15):4397-4416. Epub 2019 Jul 10.

Laboratory for Research in Neuroimaging (LREN), Department of Clinical Neuroscience, Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland.

The dopaminergic system has a unique gating function in the initiation and execution of movements. When the interhemispheric imbalance of dopamine inherent to the healthy brain is disrupted, as in Parkinson's disease (PD), compensatory mechanisms act to stave off behavioral changes. It has been proposed that two such compensatory mechanisms may be (a) a decrease in motor lateralization, observed in drug-naïve PD patients and (b) reduced inhibition - increased facilitation. Seeking to investigate the differential effect of dopamine depletion and subsequent substitution on compensatory mechanisms in non-drug-naïve PD, we studied 10 PD patients and 16 healthy controls, with patients undergoing two test sessions - "ON" and "OFF" medication. Using a simple visually-cued motor response task and fMRI, we investigated cortical motor activation - in terms of laterality, contra- and ipsilateral percent BOLD signal change and effective connectivity in the parametric empirical Bayes framework. We found that decreased motor lateralization persists in non-drug-naïve PD and is concurrent with decreased contralateral activation in the cortical motor network. Normal lateralization is not reinstated by dopamine substitution. In terms of effective connectivity, disease-related changes primarily affect ipsilaterally-lateralized homotopic cortical motor connections, while medication-related changes affect contralaterally-lateralized homotopic connections. Our findings suggest that, in non-drug-naïve PD, decreased lateralization is no longer an adaptive cortical mechanism, but rather the result of maladaptive changes, related to disease progression and long-term dopamine replacement. These findings highlight the need for the development of noninvasive therapies, which would promote the adaptive mechanisms of the PD brain.
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http://dx.doi.org/10.1002/hbm.24710DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6865418PMC
October 2019

No evidence for a common factor underlying visual abilities in healthy older people.

Dev Psychol 2019 Aug 13;55(8):1775-1787. Epub 2019 Jun 13.

Laboratory of Psychophysics.

The world's population is aging at an increasing rate. Even in the absence of neurodegenerative disorders, healthy aging affects perception and cognition. In the context of cognition, common factors are well established. Much less is known about common factors for vision. Here, we tested 92 healthy older and 104 healthy younger participants in 19 visual tests (including visual search and contrast sensitivity) and three cognitive tests (including verbal fluency and digit span). Unsurprisingly, younger participants performed better than older participants in almost all tests. Surprisingly, however, the performance of older participants was mostly uncorrelated between visual tests, and we found no evidence for a common factor. (PsycINFO Database Record (c) 2019 APA, all rights reserved).
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http://dx.doi.org/10.1037/dev0000740DOI Listing
August 2019

Running Large-Scale Simulations on the Neurorobotics Platform to Understand Vision - The Case of Visual Crowding.

Front Neurorobot 2019 29;13:33. Epub 2019 May 29.

Department of Psychological Sciences, Purdue University, West Lafayette, IN, United States.

Traditionally, human vision research has focused on specific paradigms and proposed models to explain very specific properties of visual perception. However, the complexity and scope of modern psychophysical paradigms undermine the success of this approach. For example, perception of an element strongly deteriorates when neighboring elements are presented in addition (visual crowding). As it was shown recently, the magnitude of deterioration depends not only on the directly neighboring elements but on almost all elements and their specific configuration. Hence, to fully explain human visual perception, one needs to take large parts of the visual field into account and combine all the aspects of vision that become relevant at such scale. These efforts require sophisticated and collaborative modeling. The Neurorobotics Platform (NRP) of the Human Brain Project offers a unique opportunity to connect models of all sorts of visual functions, even those developed by different research groups, into a coherently functioning system. Here, we describe how we used the NRP to connect and simulate a segmentation model, a retina model, and a saliency model to explain complex results about visual perception. The combination of models highlights the versatility of the NRP and provides novel explanations for inward-outward anisotropy in visual crowding.
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http://dx.doi.org/10.3389/fnbot.2019.00033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6549494PMC
May 2019

Motor response specificity in perceptual learning and its release by double training.

J Vis 2019 06;19(6)

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.

Perceptual learning is usually feature-specific. Recently, we showed that perceptual learning is even specific for the motor response type. In a three-line bisection task, participants indicated whether the central line was offset either to the left or right by pressing a left or a right button, respectively. We found no transfer when the same participants adjusted the offset by using a computer mouse. Here, we first show that perceptual learning with mouse adjustments transfers to the untrained hand, but only for the trained adjustment condition. There was no transfer to the button press conditions, neither for the trained nor the untrained hand. Second, we show that a double training procedure enables transfer from the mouse adjustment to the button press condition. Hence, the specificity of perceptual learning to the motor response type can be overcome by double training as it is the case for visual features. Our results suggest that during perceptual learning, perceptuo-decisional signals are encoded together with the corresponding actions.
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http://dx.doi.org/10.1167/19.6.4DOI Listing
June 2019

The unfolding argument: Why IIT and other causal structure theories cannot explain consciousness.

Conscious Cogn 2019 07 9;72:49-59. Epub 2019 May 9.

Laboratory of Psychophysics, Brain Mind Institute, EPFL, Switzerland.

How can we explain consciousness? This question has become a vibrant topic of neuroscience research in recent decades. A large body of empirical results has been accumulated, and many theories have been proposed. Certain theories suggest that consciousness should be explained in terms of brain functions, such as accessing information in a global workspace, applying higher order to lower order representations, or predictive coding. These functions could be realized by a variety of patterns of brain connectivity. Other theories, such as Information Integration Theory (IIT) and Recurrent Processing Theory (RPT), identify causal structure with consciousness. For example, according to these theories, feedforward systems are never conscious, and feedback systems always are. Here, using theorems from the theory of computation, we show that causal structure theories are either false or outside the realm of science.
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http://dx.doi.org/10.1016/j.concog.2019.04.002DOI Listing
July 2019

Beyond Bouma's window: How to explain global aspects of crowding?

PLoS Comput Biol 2019 05 10;15(5):e1006580. Epub 2019 May 10.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

In crowding, perception of an object deteriorates in the presence of nearby elements. Although crowding is a ubiquitous phenomenon, since elements are rarely seen in isolation, to date there exists no consensus on how to model it. Previous experiments showed that the global configuration of the entire stimulus must be taken into account. These findings rule out simple pooling or substitution models and favor models sensitive to global spatial aspects. In order to investigate how to incorporate global aspects into models, we tested a large number of models with a database of forty stimuli tailored for the global aspects of crowding. Our results show that incorporating grouping like components strongly improves model performance.
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http://dx.doi.org/10.1371/journal.pcbi.1006580DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6530878PMC
May 2019

Schizophrenia patients using atypical medication perform better in visual tasks than patients using typical medication.

Psychiatry Res 2019 05 6;275:31-38. Epub 2019 Mar 6.

Department of Psychiatry, Tbilisi State Medical University, Tbilisi, Georgia.

Schizophrenia (SCZ) patients show deficits in many domains, including cognition and perception. However, results are often mixed. One reason for mixed results may be differences in medication. Very little is known about the role of medication in visual processing. Here, we investigated the effects of typical vs. atypical medication on contrast sensitivity (spatial frequencies ranging from 0.2 to 20 cycles per degree), vernier acuity, and visual backward masking. From a large pool of patients, we selected 50 patients (Study 1, conducted in Brazil) and 97 patients (Study 2, conducted in Georgia) taking either only typical or atypical medication. Patients with atypical medication performed significantly better than patients with typical medication for contrast sensitivity, vernier duration, and backward masking. As a secondary result, we found similar, but not significant, trends for the cognitive tasks (Stroop, Flanker, Trail-Making Test-B, Wisconsin Card Sorting Test and Continuous Performance Test) in the same patients. No correlations were found between demographics, psychopathology, chlorpromazine equivalents and visual processing. A conclusion of our study is that one needs to be careful comparing studies when medication is not comparable.
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http://dx.doi.org/10.1016/j.psychres.2019.03.008DOI Listing
May 2019