Does binding of synesthetic color to the evoking grapheme require attention?

The official published version can be accessed from the link below.The neural mechanisms involved in binding features such as shape and color are a matter of some debate. Does accurate binding rely on spatial attention functions of the parietal lobe or can it occur without attentional input? One extraordinary phenomenon that may shed light on this question is that of chromatic-graphemic synesthesia, a rare condition in which letter shapes evoke color perceptions. A popular suggestion is that synesthesia results from cross-activation between different functional regions (e.g., between shape and color areas of the ventral pathway). Under such conditions binding may not require parietal involvement and could occur preattentively. We tested this hypothesis in two synesthetes who perceived grayscale letters and digits in color. We found no evidence for preattentive binding using a visual search paradigm in which the target was a synesthetic inducer. In another experiment involving color judgments, we show that the congruency of target color and the synesthetic color of irrelevant digits modulates performance more when the digits are included within the attended region of space. We propose that the mechanisms giving rise to this type of synesthesia appear to follow at least some principles of normal binding, and even synesthetic binding seems to require attention.This work has been supported by a Veterans Administration Senior Research Career Scientist Award and NINDS grant #MH62331 to LCR and the Elizabeth Roboz Einstein fellowship in Neuroscience and Human Development to NS

Probing the Magnetic Field Structure in Gamma-Ray Bursts through Dispersive Plasma Effects on the Afterglow Polarization

(Abr) The origin and structure of magnetic fields in Gamma-Ray Burst (GRB) fireball plasmas are two of the most important open questions in all GRB models. We show that the structure and strength of the magnetic field may be constrained by radio and IR observations of the early afterglow, where plasma effects on the polarization of propagating radiation are significant. We calculate these propagation effects for cold and relativistic plasmas, and find that in the presence of a uniform equipartition field the degree of linear polarization is suppressed, and circular polarization prevails at low frequencies, nu < 1-3 GHz, (2x10^11 Hz < nu < few x 10^14 Hz) in the forward (reverse) shock. At higher frequencies linear polarization dominates. At the frequency of the transition between circular and linear polarization, the net level of polarization is minimal, ~10-20%. These features are nearly independent of the circumburst density. The transition frequency is smaller by a factor of ~10 when the uniform field is much weaker than equipartition. The dependence of these results on viewing geometry, outflow collimation and magnetic field orientation is discussed. When the configuration of the field is entangled over length scales much smaller than the extent of the emitting plasma, the aforementioned effects should not be observed and a linear polarization at the few % level is expected. Polarimetric observations during the early afterglow, and particularly of the reverse shock emission, may therefore place strong constraints on the structure and strength of the magnetic field within the fireball plasma.Comment: 12 pages, 6 figures. Accepted for publication in ApJ. Revised version includes improved discussion of viewing and fireball geometry, with implications to resulting polarizatio

Neural fate of seen and unseen faces in visuospatial neglect: A combined event-related functional MRI and event-related potential study

This is a post print version of the article. The official published version can be obtained from the link below.To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perceived, the same stimuli produced greater activity in a distributed network of areas including right V1 and cuneus, bilateral fusiform gyri, and left parietal cortex. Also, effective connectivity between visual, parietal, and frontal areas increased during perception of faces. These results suggest that activity can occur in V1 and ventral temporal cortex without awareness, whereas coupling with dorsal parietal and frontal areas may be critical for such activity to afford conscious perception. Right parietal damage may cause a loss of awareness for contralateral (left) sensory inputs, such as hemispatial neglect and extinction (1–3). Visual extinction is the failure to perceive a stimulus in the contralesional field when presented together with an ipsilesional stimulus (bilateral simultaneous stimulation, BSS), even though occipital visual areas are intact and unilateral contralesional stimuli can be perceived when presented alone. It reflects a deficit of spatial attention toward the contralesional side, excluding left inputs from awareness in the presence of competing stimuli (2, 3). Spatial attention involves a complex neural network centered on the right parietal lobe (4, 5), but how parietal and related areas interact with sensory processing in distant cortices is largely unknown. Here we combined event-related functional MRI (fMRI) and event-related potentials (ERPs) to study the regional pattern and temporal course of brain activity produced by seen and unseen stimuli in a patient with chronic neglect and extinction caused by parietal damage. In keeping with intact early visual areas in such patients, behavioral studies suggest that some residual processing may still occur for contralesional stimuli without attention, or without awareness, including “preattentive” grouping (e.g., refs. 6 and 7) and semantic priming (e.g., ref. 8). It has been speculated (3, 9) that such effects might relate to separate cortical visual streams, with temporal areas extracting object features for identification, and parietal areas encoding spatial locations and parameters for action (10). Because neglect and extinction follow parietal damage, residual perceptual and semantic processing still might occur in occipital and temporal cortex without awareness, in the absence of normal integration with concomitant processing in parietal regions. Our study tested this hypothesis by using event-related imaging and electrophysiology measures, which are widely used to study mechanisms of normal attention (11, 12). There have been few imaging (e.g., ref. 13) or ERP (e.g., ref. 14) studies in neglect, and most examined activity at rest or during passive unilateral visual stimulation, rather than in relation to awareness or extinction on bilateral stimulation. However, a recent ERP study (15) found signals evoked by perceived, but not extinguished, visual stimuli in a parietal patient. By contrast, functional imaging in another patient (16) showed activation of striate cortex by extinguished stimuli, although severe extinction on all bilateral stimuli precluded any comparison with normal perception. In our patient we used both fMRI and ERPs during a similar extinction task to determine the neural correlates of two critical conditions: (i) when contralesional stimuli are extinguished, and (ii) when the same stimuli are seen. Stimulus presentation was arranged so as to obtain a balanced number of extinguished and seen contralesional events across all bilateral trials. Like Rees et al. (16), we used face stimuli to exploit previous knowledge that face processing activates fusiform areas in temporal cortex (e.g., refs. 17 and 18), and elicits characteristic potentials 170–200 ms after stimulus onset (e.g., refs. 19–21) in addition to other visual components such as P1 and N1 (e.g., ref. 11). We reasoned that such responses might help trace the neural fate of contralesional stimuli (seen or extinguished) at both early and later processing stages in the visual system

Specificity prediction of adenylation domains in nonribosomal peptide synthetases (NRPS) using transductive support vector machines (TSVMs)

We present a new support vector machine (SVM)-based approach to predict the substrate specificity of subtypes of a given protein sequence family. We demonstrate the usefulness of this method on the example of aryl acid-activating and amino acid-activating adenylation domains (A domains) of nonribosomal peptide synthetases (NRPS). The residues of gramicidin synthetase A that are 8 Å around the substrate amino acid and corresponding positions of other adenylation domain sequences with 397 known and unknown specificities were extracted and used to encode this physico-chemical fingerprint into normalized real-valued feature vectors based on the physico-chemical properties of the amino acids. The SVM software package SVM(light) was used for training and classification, with transductive SVMs to take advantage of the information inherent in unlabeled data. Specificities for very similar substrates that frequently show cross-specificities were pooled to the so-called composite specificities and predictive models were built for them. The reliability of the models was confirmed in cross-validations and in comparison with a currently used sequence-comparison-based method. When comparing the predictions for 1230 NRPS A domains that are currently detectable in UniProt, the new method was able to give a specificity prediction in an additional 18% of the cases compared with the old method. For 70% of the sequences both methods agreed, for <6% they did not, mainly on low-confidence predictions by the existing method. None of the predictive methods could infer any specificity for 2.4% of the sequences, suggesting completely new types of specificity

The Man Who Mistook His Neuropsychologist For a Popstar: When Configural Processing Fails in Acquired Prosopagnosia

We report the case of an individual with acquired prosopagnosia who experiences extreme difficulties in recognizing familiar faces in everyday life despite excellent object recognition skills. Formal testing indicates that he is also severely impaired at remembering pre-experimentally unfamiliar faces and that he takes an extremely long time to identify famous faces and to match unfamiliar faces. Nevertheless, he performs as accurately and quickly as controls at identifying inverted familiar and unfamiliar faces and can recognize famous faces from their external features. He also performs as accurately as controls at recognizing famous faces when fracturing conceals the configural information in the face. He shows evidence of impaired global processing but normal local processing of Navon figures. This case appears to reflect the clearest example yet of an acquired prosopagnosic patient whose familiar face recognition deficit is caused by a severe configural processing deficit in the absence of any problems in featural processing. These preserved featural skills together with apparently intact visual imagery for faces allow him to identify a surprisingly large number of famous faces when unlimited time is available. The theoretical implications of this pattern of performance for understanding the nature of acquired prosopagnosia are discussed.DY, Avery Braun, Jacob Waite, and Nadine Wanke, Bruno Rossion, Thomas Busigny and the grant awarded by AJ by the Experimental Psychology Society (EPS

On The Power of Tree Projections: Structural Tractability of Enumerating CSP Solutions

The problem of deciding whether CSP instances admit solutions has been deeply studied in the literature, and several structural tractability results have been derived so far. However, constraint satisfaction comes in practice as a computation problem where the focus is either on finding one solution, or on enumerating all solutions, possibly projected to some given set of output variables. The paper investigates the structural tractability of the problem of enumerating (possibly projected) solutions, where tractability means here computable with polynomial delay (WPD), since in general exponentially many solutions may be computed. A general framework based on the notion of tree projection of hypergraphs is considered, which generalizes all known decomposition methods. Tractability results have been obtained both for classes of structures where output variables are part of their specification, and for classes of structures where computability WPD must be ensured for any possible set of output variables. These results are shown to be tight, by exhibiting dichotomies for classes of structures having bounded arity and where the tree decomposition method is considered

Dance Across Cultures: Joint Action Aesthetics in Japan and the UK

Copyright © The Author(s) 2021. Western European and East Asian cultures show marked differences in aesthetic appreciation of the visual arts. East Asian aesthetics are often associated with a holistic focus on balance and harmony, in contrast to Western aesthetics, which often focus on the expression of the individual. In this study, we examined whether cultural differences also exist in relation to the aesthetics of dance. Japanese and British participants completed an online survey in which they evaluated synchronous and asynchronous dance video clips on eight semantic differential scales. We observed that the aesthetics of group dance depend on cultural background. Specifically, British participants preferred asynchronous over synchronous dance whereas Japanese participants equally liked synchronous and asynchronous dance movement. For both cultures, preferences were based on distinct semantic associations with movement synchrony. We argue that cultural differences in aesthetic perception of group dance relate to the culturally specific social signals conveyed by unison movement.ESRC transformative research grant (ES/M000680/2) on “Synchronous movement, cooperation, and the Performing Arts”; Colombian Administrative Department of Science, Technology and Innovation (Colciencias); Universidad del Norte

Collective processes in relativistic plasma and their implications for gamma-ray burst afterglows

We consider the effects of collective plasma processes on synchrotron emission from highly relativistic electrons. We find, in agreement with Sazonov (1970), that strong effects are possible also in the absence of a non-relativistic plasma component, due to the relativistic electrons (and protons) themselves. In contrast with Sazonov, who infers strong effects only in cases where the ratio of plasma frequency to cyclotron frequency is much larger than the square of the characteristic electron Lorentz factor, nu_p/nu_B >> gamma^2, we find strong effects also for 1 << nu_p/nu_B << gamma^2. The modification of the spectrum is prominent at frequencies nu < nu_{R*} = nu_p min[gamma, (nu_p/nu_B)^(1/2)], where nu_{R*} generalizes the Razin-Tsytovich frequency, nu_R = gamma nu_p, to the regime nu_p/nu_B << gamma^2. Applying our results to gamma-ray burst (GRB) plasmas, we predict a strong modification of the radio spectrum on minute time scale following the GRB, at the onset of fireball interaction with its surrounding medium, in cases where the ratio of the energy carried by the relativistic electrons to the energy carried by the magnetic field exceeds ~ 10^5. Plausible electron distribution functions may lead to negative synchrotron reabsorption, i.e to coherent radio emission, which is characterized by a low degree of circular polarization. Detection of these effects would constrain the fraction of energy in the magnetic field, which is currently poorly determined by observations, and, moreover, would provide a novel handle on the properties of the environment into which the fireball expands.Comment: 28 pages, 1 figure, submitted to Ap

Interprocedural shape analysis for effectively cutpoint-free programs

Abstract. We present a framework for local interprocedural shape analysis that computes procedure summaries as transformers of procedure-local heaps (the parts of the heap that the procedure may reach). A main challenge in procedurelocal shape analysis is the handling of cutpoints, objects that separate the input heap of an invoked procedure from the rest of the heap, which-from the viewpoint of that invocation-is non-accessible and immutable. In this paper, we limit our attention to effectively cutpoint-free programsprograms in which the only objects that separate the callee&apos;s heap from the rest of the heap, when considering live reference fields, are the ones pointed to by the actual parameters of the invocation. This limitation (and certain variations of it, which we also describe) simplifies the local-reasoning about procedure calls because the analysis needs not track cutpoints. Furthermore, our analysis (conservatively) verifies that a program is effectively cutpoint-free