Methods to assess binocular rivalry with periodic stimuli

This is the final version. Available on open access from SpringerOpen via the DOI in this recordAvailability of data and materials: Source code for the model is available in the GitHub repository farzaneh-darki/Darki2020_methods: https://github.com/farzaneh-darki/Darki2020_methods.Binocular rivalry occurs when the two eyes are presented with incompatible stimuli and perception alternates between these two stimuli. This phenomenon has been investigated in two types of experiments: (1) Traditional experiments where the stimulus is fixed, (2) eye-swap experiments in which the stimulus periodically swaps between eyes many times per second (Logothetis et al. in Nature 380(6575):621–624, 1996). In spite of the rapid swapping between eyes, perception can be stable for many seconds with specific stimulus parameter configurations. Wilson introduced a two-stage, hierarchical model to explain both types of experiments (Wilson in Proc. Natl. Acad. Sci. 100(24):14499–14503, 2003). Wilson’s model and other rivalry models have been only studied with bifurcation analysis for fixed inputs and different types of dynamical behavior that can occur with periodically forcing inputs have not been investigated. Here we report (1) a more complete description of the complex dynamics in the unforced Wilson model, (2) a bifurcation analysis with periodic forcing. Previously, bifurcation analysis of the Wilson model with fixed inputs has revealed three main types of dynamical behaviors: Winner-takes-all (WTA), Rivalry oscillations (RIV), Simultaneous activity (SIM). Our results have revealed richer dynamics including mixed-mode oscillations (MMOs) and a period-doubling cascade, which corresponds to low-amplitude WTA (LAWTA) oscillations. On the other hand, studying rivalry models with numerical continuation shows that periodic forcing with high frequency (e.g. 18 Hz, known as flicker) modulates the three main types of behaviors that occur with fixed inputs with forcing frequency (WTA-Mod, RIV-Mod, SIM-Mod). However, dynamical behavior will be different with low frequency periodic forcing (around 1.5 Hz, so-called swap). In addition to WTA-Mod and SIM-Mod, cycle skipping, multi-cycle skipping and chaotic dynamics are found. This research provides a framework for either assessing binocular rivalry models to check consistency with empirical results, or for better understanding neural dynamics and mechanisms necessary to implement a minimal binocular rivalry model.Engineering and Physical Sciences Research Council (EPSRC

Assessment of extreme productivity of microalgae cultivated in the open air around neighborhoods of Isfahan City

The widespread use of microalgae in various fields of human activity including fishery generated a need of highly productive technologies of industrial production of microalgae biomass. In present paper, extreme productivity values of microalgae culturing system were assessed around neighborhoods of the Isfahan City in theory. It will amount to 37.90 g of dry weight (g. d. w.) per 1 m^2 of the illuminated reactor surface under condition that efficiency factor of photobiosynthesis equals to 5%. When photobiosynthetic efficiency is 15%, maximum values of productivity will be 113.71 g. d. w. per 1 m^2. Productivity of microalgae culturing system for its various orientations relative to the Sun at different photobiosynthetic efficiency was calculated on basis of simple model understandings regarding average caloric content of 1 g.d.w. of microalgae and the daily distribution of solar radiation which arrives at the surface of the Earth. If it is drown a curve of the third order (spline) through the points corresponding to days of the vernal (21 March) and autumnal (21 September) equinoxes and a summer solstice (22 June), the extreme (ideal) value of the yield will be 18.5 kg of dry biomass per square meter of illuminated surface (at photobiosynthetic efficiency of 0.15)

Neural dynamics of perceptual competition

This research aims to understand the neural dynamics and mechanisms underlying perceptual bistability. In perceptual rivalry, ambiguous sensory information leads to dynamic changes in the perceptual interpretation of fixed stimuli. This phenomenon occurs when participants receive sensory stimuli that support two or more distinct interpretations; this results in spontaneous alternations between possible perceptual interpretations. Perceptual rivalry has been widely studied across different sensory modalities including vision, audition, and to a limited extent, in the tactile domain. Common features of perceptual rivalry across various ambiguous visual and auditory paradigms characterise the randomness of switching times and their dependence on input strength manipulations (Levelt's propositions). Binocular rivalry occurs when the two eyes are presented with incompatible stimuli and perception alternates between these two stimuli. This phenomenon has been investigated in two types of experiments: 1) Traditional experiments where the stimulus is fixed, 2) Eye-swap experiments in which stimulus periodically swaps between eyes many times per second~\citep{logothetis1996rivalling}. In spite of the rapid swapping between eyes, perception can be stable for many seconds with specific stimulus parameter configurations. Wilson introduced a two-stage, hierarchical model to explain both types of experiments~\citep{wilson2003computationala}. Wilson's model and other rivalry models have been only studied with bifurcation analysis for fixed inputs and different dynamical behaviours that can occur with periodic forcing have yet to be explored. Here I report 1) a more complete description of the complex dynamics in the unforced Wilson model, 2) a bifurcation analysis with periodic forcing. Previously, bifurcation analysis of the Wilson model with fixed inputs has revealed three main types of dynamical behaviours: Winner-take-all (WTA), Rivalry oscillations (RIV), Simultaneous activity (SIM). The results presented here reveal richer dynamics including mixed-mode oscillations (MMOs) and period-doubling cascade which corresponds to low amplitude WTA (LAWTA) oscillations. On the other hand, studying rivalry models with numerical continuation shows that periodic forcing with high frequency (e.g. 18 Hz, known as flicker) modulates the three main types of behaviours that occur with fixed inputs by the forcing frequency (WTA-Mod, RIV-Mod, SIM-Mod). However, the dynamical behaviour will be different with low frequency periodic forcing (around 1.5Hz, so-called swap), and in addition to WTA-Mod and SIM-Mod, cycle skipping and multi-cycle skipping behaviour exist, which can also lead to chaotic dynamics. This research provides a framework for either assessing binocular rivalry models for consistency checks against empirical results, or for better understanding neural dynamics and the mechanisms necessary to implement a minimal binocular rivalry model.\\ At present, it remains unclear whether the general characteristics of perceptual rivalry are preserved with tactile stimuli. I introduce a simple tactile stimulus capable of generating perceptual rivalry and explore whether general features of perceptual rivalry from other modalities extend to the tactile domain. In these experiments, vibrotactile stimuli consisted of anti-phase sequences of high and low intensity high-frequency pulses, each followed by a silent interval, delivered to the right and left index fingers. Participants perceived the stimulus as either one simultaneous pattern of vibration on both hands (SIM), or patterns of vibration that jumped from one hand to the other hand, giving a sensation of apparent movement (AM). For long stimulus presentations, perception switches back and forth between these two percepts. Furthermore, my results confirm that Levelt's proposition II extends to tactile bistability, and that the stochastic characteristics of irregular perceptual alternations agree with non-tactile modalities. An analysis of correlations between subsequent perceptual phases reveals a significant positive correlation at lag 1 (as found in visual bistability), and a negative correlation for lag 2 (in contrast with visual bistability). In this study, a mathematical model of tactile rivalry is developed that focuses on accurately reproducing the dynamics of the perceptual alternations. The model of tactile rivalry presented here consists of two processing stages; first stage for producing perceptual alternations; and a second stage for encoding the percept types (SIM and AM). Putative neural populations of the first stage could be located early in the somatosensory pathway at brainstem nuclei, and the neural populations of the second stage could be located within area 3b of the primary somatosensory cortex, based on excitatory and lagged inhibitory components of their receptive fields. The powerful combination of bifurcation analysis along with optimisation tools have been used to tune certain features of the model, resulting in a good qualitative and quantitative match to my experimental data. As well as capturing the dynamical characteristics specific to the perceptual interpretations in tactile rivalry, the model presented here is able to produce the general characteristics of perceptual rivalry including Levelt's proposition, short-tailed skewness of reversal time distributions and a scaling property of this distribution's first three moments.Engineering and Physical Sciences Research Council (EPSRC

White matter connections : developmental neuroimaging studies of the associations between genes, brain and behavior

Development of cognitive abilities across childhood and adulthood parallels brain maturation in typically developing samples. Cognitive abilities such as reading and working memory have been linked to neuroimaging measures in relevant brain regions. Though the correlations between inter-individual brain differences and their related cognitive abilities are well established, the cause of this inter-individual variability is still not fully known. This thesis aims to understand the neural bases of the inter-individual variability in reading ability by studying the associations between dyslexia susceptibility genes and white and gray matter brain structures, and determine whether the measures of associated regions correlate with variability in reading ability. Moreover, it aims to identify the brain measures that correlate with concurrent measures of working memory and those that are predictive of future working memory, using a longitudinal cohort of typically developing children and young adults. Studies I and II: Three genes, DYX1C1, DCDC2 and KIAA0319, have been previously associated with dyslexia, neuronal migration, and ciliary function. We investigated whether the polymorphisms within these genes would affect variability in white and gray matter brain structures. Rs3743204 (DYX1C1), rs793842 (DCDC2), and rs6935076 (KIAA0319) were associated with left temporo-parietal white matter volume connecting middle temporal cortex to angular and supramarginal gyri as well as lateral occipital cortex. Rs793842 was significantly associated with thickness of left parietal areas and the lateral occipital cortex. Both white and gray matter measures correlated with current reading ability, but only white matter predicted future reading. Study III: We aimed to investigate whether MRPL19/C2ORF3 dyslexia genes, found to be correlated with verbal and non-verbal IQ, have a significant influence on white matter brain structures. Rs917235 showed a significant association with white matter volume in bilateral posterior parts of the corpus callosum and the cingulum, with connections to parietal, occipital and temporal cortices that are involved in both language and general cognitive abilities. Study IV: ROBO1 is a dyslexia gene that has been associated with axonal guidance and midline crossing. We assessed whether the polymorphisms within this gene have an influence on structure of the corpus callosum. Rs7631357 was associated with probability of connections within the fibers extending through the body of corpus callosum to parietal brain regions. The results fit well with previous reports on the role of Robo1 in axonal path finding in mice. Study V: Working memory has been associated with greater brain activity, thinner cortex, and white matter maturation in cross-sectional studies of children and young adults. Here, we aimed to investigate the role of differences in brain structure and function in the development of working memory. We assessed the concurrent and predictive relationships between working memory performance and neuroimaging measures in the fronto-parietal and fronto-striatal networks important for working memory. Working memory performance correlated with brain activity in frontal and parietal regions, cortical thickness in parietal cortex, and white matter volume of fronto-parietal and fronto-striatal tracts. White matter microstructure and brain activity in the caudate predicted future working memory. This work highlights the impact of imaging genetics research, revealing important associations between genes, brain and behavior. The results identify the neural mechanism underlying two cognitive abilities, reading and working memory. Specifically, the findings identify the important role of white matter in driving the development of working memory and reading ability, connecting the related cortical areas, as well as bridging the gap between genes and behavior

Perceptual rivalry with vibrotactile stimuli

This is the final version. Available on open access from Springer via the DOI in this recordAvailability of data and materials: The datasets generated and analyzed during the current study are available in the GitHub repository farzaneh-darki/Darki2021_perceptual: https://github.com/farzaneh-darki/Darki2021_perceptual.In perceptual rivalry, ambiguous sensory information leads to dynamic changes in the perceptual interpretation of fixed stimuli. This phenomenon occurs when participants receive sensory stimuli that support two or more distinct interpretations; this results in spontaneous alternations between possible perceptual interpretations. Perceptual rivalry has been widely studied across different sensory modalities including vision, audition, and to a limited extent, in the tactile domain. Common features of perceptual rivalry across various ambiguous visual and auditory paradigms characterize the randomness of switching times and their dependence on input strength manipulations (Levelt’s propositions). It is still unclear whether the general characteristics of perceptual rivalry are preserved with tactile stimuli. This study aims to introduce a simple tactile stimulus capable of generating perceptual rivalry and explores whether general features of perceptual rivalry from other modalities extend to the tactile domain. Our results confirm that Levelt’s proposition II extends to tactile bistability, and that the stochastic characteristics of irregular perceptual alternations agree with non-tactile modalities. An analysis of correlations between subsequent perceptual phases reveals a significant positive correlation at lag 1 (as found in visual bistability), and a negative correlation for lag 2 (in contrast with visual bistability).Engineering and Physical Sciences Research Council (EPSRC

Analysis of the tube piercing process types in terms of final product properties

The rotary tube piercing (RTP) is the first process of making seamless tube after producing the desired alloy ingot. There are several ways to make a seamless tube, one of the most common being RTP. This approach covers a wide range of processes that are categorized according to the number and shape of the rollers. On the other hand, each of these types has designed guides in the output and input of the piercing process. In this article, a new design of input and output guide for all types of rollers have been examined and simulated. Thus, three specimens including Diescher and Conical rollers were considered with 3 and 2 numbers, respectively. Results including torque, total force, temperature distribution and strain were extracted using FEM simulation. The results obtained through simulation are more in line with the experimental results obtained from previous research. While showing the successful performance of the output and input guides of the RTP process, the results indicate that the 3-roller Diescher type RTP has the most suitable arrangement for seamless tube production. © 2021 DAAAM International. All rights reserved

Human ROBO1 regulates white matter structure in corpus callosum

The axon guidance receptor, Robo1, controls the pathfinding of callosal axons in mice. To determine whether the orthologous ROBO1 gene is involved in callosal development also in humans, we studied polymorphisms in the ROBO1 gene and variation in the white matter structure in the corpus callosum using both structural magnetic resonance imaging and diffusion tensor magnetic resonance imaging. We found that five polymorphisms in the regulatory region of ROBO1 were associated with white matter density in the posterior part of the corpus callosum pathways. One of the polymorphisms, rs7631357, was also significantly associated with the probability of connections to the parietal cortical regions. Our results demonstrate that human ROBO1 may be involved in the regulation of the structure and connectivity of posterior part of corpus callosum.Peer reviewe

Utility of Blood Cellular Indices in the Risk Stratification of Patients Presenting with Acute Pulmonary Embolism.

Pulmonary embolism (PE) clinical manifestations vary widely, and that scope is not fully captured by current all-cause mortality risk models. PE is associated with inflammatory, coagulation, and hemostatic imbalances so blood cellular indices may be prognostically useful. Complete blood count (CBC) data may improve current risk models like the simplified pulmonary embolism severity index (sPESI) for all-cause mortality, offering greater accuracy and analytic ability. Acute PE patients (n = 228) with confirmatory diagnostic imaging were followed for all-cause mortality. Blood cellular indices were assessed for association to all-cause mortality and were supplemented into sPESI using multivariate logistic regression. Multiple blood cellular indices were found to be significantly associated with all-cause mortality in acute PE. sPESI including red cell distribution width, hematocrit and neutrophil-lymphocyte ratio had better predictive ability as compared to sPESI alone (AUC: 0.852 vs 0.754). Blood cellular indices contribute an inflammatory and hemodynamic perspective not currently included in sPESI. CBC with differential is a widely used, low-cost test that can augment current risk stratification tools for all-cause mortality in acute PE patients

Mutation in CEP63 co-segregating with developmental dyslexia in a Swedish family

Developmental dyslexia is the most common learning disorder in children. Problems in reading and writing are likely due to a complex interaction of genetic and environmental factors, resulting in reduced power of studies of the genetic factors underlying developmental dyslexia. Our approach in the current study was to perform exome sequencing of affected and unaffected individuals within an extended pedigree with a familial form of developmental dyslexia. We identified a two-base mutation, causing a p.R229L amino acid substitution in the centrosomal protein 63 kDa (CEP63), co-segregating with developmental dyslexia in this pedigree. This mutation is novel, and predicted to be highly damaging for the function of the protein. 3D modelling suggested a distinct conformational change caused by the mutation. CEP63 is localised to the centrosome in eukaryotic cells and is required for maintaining normal centriole duplication and control of cell cycle progression. We found that a common polymorphism in the CEP63 gene had a significant association with brain white matter volume. The brain regions were partly overlapping with the previously reported region influenced by polymorphisms in the dyslexia susceptibility genes DYX1C1 and KIAA0319. We hypothesise that CEP63 is particularly important for brain development and might control the proliferation and migration of cells when those two events need to be highly coordinated.Peer reviewe