Processing Of Shape Information Research Articles

Delayed processing of global shape information in developmental prosopagnosia.

There is accumulating evidence suggesting that a central deficit in developmental prosopagnosia (DP), a disorder characterized by profound and lifelong difficulties with face recognition, concerns impaired holistic processing. Some of this evidence comes from studies using Navon’s paradigm where individuals with DP show a greater local or reduced global bias compared with controls. However, it has not been established what gives rise to this altered processing bias. Is it a reduced global precedence effect, changes in susceptibility to interference effects or both? By analyzing the performance of 10 individuals with DP in Navon’s paradigm we find evidence of a reduced global precedence effect: The DPs are slower than controls to process global but not local shape information. Importantly, and in contrast to previous studies, we demonstrate that the DPs perform normally in a comprehensive test of visual attention, showing normal: visual short-term memory capacity, speed of visual processing, efficiency of top-down selectivity, and allocation of attentional resources. Hence, we conclude that the reduced global precedence effect reflects a perceptual rather than an attentional deficit. We further show that this reduced global precedence effect correlates both with the DPs’ face recognition abilities, as well as their ability to recognize degraded (non-face) objects. We suggest that the DPs’ impaired performance in all three domains (Navon, face and object recognition) may be related to the same dysfunction; delayed derivation of global relative to local shape information.

Serotonin Decreases the Gain of Visual Responses in Awake Macaque V1.

Serotonin, an important neuromodulator in the brain, is implicated in affective and cognitive functions. However, its role even for basic cortical processes is controversial. For example, in the mammalian primary visual cortex (V1), heterogenous serotonergic modulation has been observed in anesthetized animals. Here, we combined extracellular single-unit recordings with iontophoresis in awake animals. We examined the role of serotonin on well-defined tuning properties (orientation, spatial frequency, contrast, and size) in V1 of two male macaque monkeys. We find that in the awake macaque the modulatory effect of serotonin is surprisingly uniform: it causes a mainly multiplicative decrease of the visual responses and a slight increase in the stimulus-selective response latency. Moreover, serotonin neither systematically changes the selectivity or variability of the response, nor the interneuronal correlation unexplained by the stimulus (“noise-correlation”). The modulation by serotonin has qualitative similarities with that for a decrease in stimulus contrast, but differs quantitatively from decreasing contrast. It can be captured by a simple additive change to a threshold-linear spiking nonlinearity. Together, our results show that serotonin is well suited to control the response gain of neurons in V1 depending on the animal's behavioral or motivational context, complementing other known state-dependent gain-control mechanisms.SIGNIFICANCE STATEMENT Serotonin is an important neuromodulator in the brain and a major target for drugs used to treat psychiatric disorders. Nonetheless, surprisingly little is known about how it shapes information processing in sensory areas. Here we examined the serotonergic modulation of visual processing in the primary visual cortex of awake behaving macaque monkeys. We found that serotonin mainly decreased the gain of the visual responses, without systematically changing their selectivity, variability, or covariability. This identifies a simple computational function of serotonin for state-dependent sensory processing, depending on the animal's affective or motivational state.

Novel method of extracting motion from natural movies

BackgroundThe visual system in primates can be segregated into motion and shape pathways. Interaction occurs at multiple stages along these pathways. Processing of shape-from-motion and biological motion is considered to be a higher-order integration process involving motion and shape information. However, relatively limited types of stimuli have been used in previous studies on these integration processes. New methodWe propose a new algorithm to extract object motion information from natural movies and to move random dots in accordance with the information. The object motion information is extracted by estimating the dynamics of local normal vectors of the image intensity projected onto the x-y plane of the movie. ResultsAn electrophysiological experiment on two adult common marmoset monkeys (Callithrix jacchus) showed that the natural and random dot movies generated with this new algorithm yielded comparable neural responses in the middle temporal visual area. Comparison with existing methodsIn principle, this algorithm provided random dot motion stimuli containing shape information for arbitrary natural movies. This new method is expected to expand the neurophysiological and psychophysical experimental protocols to elucidate the integration processing of motion and shape information in biological systems. ConclusionsThe novel algorithm proposed here was effective in extracting object motion information from natural movies and provided new motion stimuli to investigate higher-order motion information processing.

Spatial dispersal of bacterial colonies induces a dynamical transition from local to global quorum sensing.

Bacteria communicate using external chemical signals called autoinducers (AI) in a process known as quorum sensing (QS). QS efficiency is reduced by both limitations of AI diffusion and potential interference from neighboring strains. There is thus a need for predictive theories of how spatial community structure shapes information processing in complex microbial ecosystems. As a step in this direction, we apply a reaction-diffusion model to study autoinducer signaling dynamics in a single-species community as a function of the spatial distribution of colonies in the system. We predict a dynamical transition between a local quorum sensing (LQS) regime, with the AI signaling dynamics primarily controlled by the local population densities of individual colonies, and a global quorum sensing (GQS) regime, with the dynamics being dependent on collective intercolony diffusive interactions. The crossover between LQS to GQS is intimately connected to a trade-off between the signaling network's latency, or speed of activation, and its throughput, or the total spatial range over which all the components of the system communicate.

Early differential sensitivity of evoked-potentials to local and global shape during the perception of three-dimensional objects

Here we investigated the time course underlying differential processing of local and global shape information during the perception of complex three-dimensional (3D) objects. Observers made shape matching judgments about pairs of sequentially presented multi­part novel objects. Event-related potentials (ERPs) were used to measure perceptual sensitivity to 3D shape differences in terms of local part structure and global shape configuration – based on predictions derived from hierarchical structural description models of object recognition. There were three types of different object trials in which stimulus pairs (1) shared local parts but differed in global shape configuration; (2) contained different local parts but shared global configuration or (3) shared neither local parts nor global configuration. Analyses of the ERP data showed differential amplitude modulation as a function of shape similarity as early as the N1 component between 146–215ms post-stimulus onset. These negative amplitude deflections were more similar between objects sharing global shape configuration than local part structure. Differentiation among all stimulus types was reflected in N2 amplitude modulations between 276–330ms. sLORETA inverse solutions showed stronger involvement of left occipitotemporal areas during the N1 for object discrimination weighted towards local part structure. The results suggest that the perception of 3D object shape involves parallel processing of information at local and global scales. This processing is characterised by relatively slow derivation of ‘fine-grained’ local shape structure, and fast derivation of ‘coarse-grained’ global shape configuration. We propose that the rapid early derivation of global shape attributes underlies the observed patterns of N1 amplitude modulations.

Modality-specific spectral dynamics in response to visual and tactile sequential shape information processing tasks: An MEG study using multivariate pattern classification analysis

Brain regions that respond to more than one sensory modality are characterized as multisensory regions. Studies on the processing of shape or object information have revealed recruitment of the lateral occipital cortex, posterior parietal cortex, and other regions regardless of input sensory modalities. However, it remains unknown whether such regions show similar (modality-invariant) or different (modality-specific) neural oscillatory dynamics, as recorded using magnetoencephalography (MEG), in response to identical shape information processing tasks delivered to different sensory modalities. Modality-invariant or modality-specific neural oscillatory dynamics indirectly suggest modality-independent or modality-dependent participation of particular brain regions, respectively. Therefore, this study investigated the modality-specificity of neural oscillatory dynamics in the form of spectral power modulation patterns in response to visual and tactile sequential shape-processing tasks that are well-matched in terms of speed and content between the sensory modalities. Task-related changes in spectral power modulation and differences in spectral power modulation between sensory modalities were investigated at source-space (voxel) level, using a multivariate pattern classification (MVPC) approach. Additionally, whole analyses were extended from the voxel level to the independent-component level to take account of signal leakage effects caused by inverse solution. The modality-specific spectral dynamics in multisensory and higher-order brain regions, such as the lateral occipital cortex, posterior parietal cortex, inferior temporal cortex, and other brain regions, showed task-related modulation in response to both sensory modalities. This suggests modality-dependency of such brain regions on the input sensory modality for sequential shape-information processing.

Towards Predictive Modeling of Information Processing in Microbial Ecosystems with Quorum Sensing Interactions

Bacteria communicate using external chemical signals in a process known as quorum sensing. However, the efficiency of this communication is reduced by both limitations on the rate of diffusion over long distances and potential interference from neighboring strains. Therefore, having a framework to quantitatively predict how spatial structure and biodiversity shape information processing in bacterial colonies is important, both for understanding the evolutionary dynamics of natural microbial ecosystems, and for the rational design of synthetic ecosystems with desired computational properties.As a first step towards these goals, we implement a reaction-diffusion model to study the dynamics of a LuxI/LuxR quorum sensing circuit in a growing bacterial population. The spatiotemporal concentration profile of acyl-homoserine lactone (AHL) signaling molecules is analyzed, and used to define a measure of physical and functional signaling network connectivity. From this, we systematically investigate how different initial distributions of bacterial populations influence the subsequent efficiency of collective long-range signal propagation in the population. We compare our results with known experimental data, and discuss limitations and extensions to our modeling framework.

Online processing of shape information for control of grasping.

When picking up objects, we tend to grasp at contact points that minimize slippage and torsion, which depend on the particular shape. Normally, grasp points could be planned before initiating movement. We tested whether grasp points can be determined during online control. Subjects reached to grasp virtual planar objects with varied shapes. On some trials, the object was changed during movement, either rotated by 45° or replaced with a different object. In all conditions, grasp axes were well adapted to the target shape, passing near the center of mass with low force closure angles. On perturbed trials, corrective adjustments were detectable within 320ms and were toward the same grasp axes observed on unperturbed trials. Perturbations had little effect on either kinematics or the optimality of final grasp points. Our results demonstrate that the visuomotor system is capable of online processing of shape information to determine appropriate contact points for grasping.

The Prototype of Indicators of a Responsive Partner Shapes Information Processing: A False Recognition Study

ABSTRACTWhen judging whether a relationship partner can be counted on to “be there” when needed, people may draw upon knowledge structures to process relevant information. We examined one such knowledge structure using the prototype methodology: indicators of a partner who is likely to be there when needed. In the first study (N = 91), the structure, content, and reliability of the prototype of indicators were examined. Then, using a false recognition study (N = 77), we demonstrated that once activated, the prototype of indicators of a partner who is likely to be there when needed affects information processing. Thus, the prototype of indicators may shape how people process support-relevant information in everyday life, affecting relationship outcomes. Using this knowledge structure may help a person process relevant information quickly and with cognitive economy. However, it may also lead to biases in judgments in certain situations.

Can we simulate an action that we temporarily cannot perform?

The scope of individuals' motor repertoire and expertise influences the way they perceive the actions of others. When observing skilled actions, experts recruit the cortical network subserving action perception (action observation network, AON) to a greater extent than non-experts. However, it remains unknown whether and how a temporary motor injury affects activation within the AON. To investigate this issue, brain hemodynamic activity was recorded twice in thirteen national female gymnasts suffering from a lower extremity injury at the onset of the experiment. The gymnasts were scanned one month after the injury and were shown gymnastics routines they were able and temporarily unable to perform. Six months later, after complete recovery, they were scanned again and shown the same routines they were now able to practice. Results showed: first, that the level of activity within the inferior parietal lobule and MT/V5/EBA (extrastriate body area), areas constitutive of the AON, was independent of the gymnasts' physical condition. Second, when gymnasts were hurt (vs. when recovered), higher activity in the cerebellum was detected. The equal contribution of MT/V5/EBA and inferior parietal lobule during the observation of movements the gymnasts were able or unable to practice suggests respectively that physical provisional incapacity does not interfere with the perceptual processing of body shape and motion information, and that motor expertise may prevent the decay of sensorimotor representations. Higher activations in the cerebellum may suggest that this structure plays a role in dissociating perceived physically feasible movements from those that are provisionally unfeasible.

Fast Processing of Shape Information for Online Control of Grasping

The graph plots mean grasp axis angle as a function of time after reaching the point 20cm away from the object, which corresponds to the onset of perturbations. Grasp axes were normalized by subtracting the average of the unperturbed 0° and 45° conditions for each object. The graph plots mean grasp axis angle as a function of time after the perturbation onset. Grasp axes were normalized and scaled by mapping the mean nal grasp axis of the original object to -1.0 and the post-perturbation object to 1.0. 1.0

Powerful inhibitory action of mu opioid receptors (MOR) on cholinergic interneuron excitability in the dorsal striatum

Cholinergic interneurons (ChIs) of dorsal striatum play a key role in motor control and in behavioural learning. Neuropeptides regulate cholinergic transmission and mu opioid receptor (MOR) activation modulates striatal acetylcholine release. However, the mechanisms underlying this effect are yet uncharacterized. Here, we examined the electrophysiological responses of ChIs to the selective MOR agonist, DAMGO {[D-Ala2-MePhe4-Gly(ol)5] enkephalin}. We observed a robust, dose-dependent inhibition of spontaneous firing activity (0.06–3 μM) which was reversible upon drug washout and blocked by the selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) (1 μM). Voltage-clamp analysis of the reversal potential of the DAMGO effect did not provide univocal results, indicating the involvement of multiple membrane conductances. The MOR-dependent effect persisted in the presence of GABAA and ionotropic glutamate receptor antagonists, ruling out an indirect effect. Additionally, it depended upon G-protein activation, as it was prevented by intrapipette GDP-β-S. Because D2 dopamine receptors (D2R) and MOR share a common post-receptor signalling pathway, occlusion experiments were performed with maximal doses of both D2R and MOR agonists. The D2R agonist quinpirole decreased spike discharge, which was further reduced by adding DAMGO. Then, D2R or MOR antagonists were used to challenge the response to the respective agonists, DAMGO or quinpirole. No cross-effect was observed, suggesting that the two receptors act independently.Our findings demonstrate a postsynaptic inhibitory modulation by MOR on ChIs excitability. Such opioidergic regulation of cholinergic transmission might contribute to shape information processing in basal ganglia circuits, and represent a potential target for pharmacological intervention.

High and low performers differ in the use of shape information for face recognition

Previous findings demonstrated that increasing facial distinctiveness by means of spatial caricaturing improves face learning and results in modulations of event-related-potential (ERP) components associated with the processing of typical shape information (P200) and with face learning and recognition (N250). The current study investigated performance-based differences in the effects of spatial caricaturing: a modified version of the Bielefelder famous faces test (BFFT) was applied to subdivide a non-clinical group of 28 participants into better and worse face recognizers. Overall, a learning benefit was seen for caricatured compared to veridical faces. In addition, for learned faces we found larger caricaturing effects in response times, inverse efficiency scores as well as in P200 and N250 amplitudes in worse face recognizers, indicating that these individuals profited disproportionately from exaggerated idiosyncratic face shape. During learning and for novel faces at test, better and worse recognizers showed similar caricaturing effects. We suggest that spatial caricaturing helps better and worse face recognizers accessing critical idiosyncratic shape information that supports identity processing and learning of unfamiliar faces. For familiarized faces, better face recognizers might depend less on exaggerated shape and make better use of texture information than worse recognizers. These results shed light on the transition from unfamiliar to familiar face processing and may also be relevant for developing training-programmes for people with difficulties in face recognition.

The role of semantic abstractness and perceptual category in processing speech accompanied by gestures

Space and shape are distinct perceptual categories. In language, perceptual information can also be used to describe abstract semantic concepts like a “rising income” (space) or a “square personality” (shape). Despite being inherently concrete, co-speech gestures depicting space and shape can accompany concrete or abstract utterances. Here, we investigated the way that abstractness influences the neural processing of the perceptual categories of space and shape in gestures. Thus, we tested the hypothesis that the neural processing of perceptual categories is highly dependent on language context. In a two-factorial design, we investigated the neural basis for the processing of gestures containing shape (SH) and spatial information (SP) when accompanying concrete (c) or abstract (a) verbal utterances. During fMRI data acquisition participants were presented with short video clips of the four conditions (cSP, aSP, cSH, aSH) while performing an independent control task. (a) as opposed to concrete (c) utterances activated temporal lobes bilaterally and the left inferior frontal gyrus (IFG) for both shape-related (SH) and space-related (SP) utterances. An interaction of perceptual category and semantic abstractness in a more anterior part of the left IFG and inferior part of the posterior temporal lobe (pTL) indicates that abstractness strongly influenced the neural processing of space and shape information. Despite the concrete visual input of co-speech gestures in all conditions, space and shape information is processed differently depending on the semantic abstractness of its linguistic context.

Further evidence that local cues to shape in RF patterns are integrated globally

Radial frequency (RF) patterns, paths deformed from circular by a sinusoidal modulation of radius, have proved valuable stimuli for investigation of visual shape processing. Their utility relies upon evidence that thresholds for detection of modulation decrease, as cycles of modulation are added, at a rate that cannot be accounted for by the improving probability of detection of any single cycle (probability summation). This has been interpreted as indicative of global processing. Recently Mullen, Beaudot, and Ivanov (2011), using low contrast RF patterns viewed in cosine phase through a Gaussian window, demonstrated the existence of a local cue to modulation that was more salient than the global shape cue present in sectors of RF patterns. The experiments reported here investigate why this cue has not previously obscured global integration of shape information in RF patterns. Using stimuli modulated in sine phase, Experiment 1 showed that the presence of a circular sector of path, used to complete a partially modulated RF pattern, does not raise thresholds, contrary to the suggestion of Mullen et al. (2011). Experiment 2 demonstrated integration for high and low contrast RF patterns viewed in sine phase through a Gaussian window and Experiment 3 showed the same for patterns in cosine phase if the use of a local phase specific curvature cue was precluded. Effective use of local curvature in the test comparison, then, requires knowledge of pattern orientation to define the sign of curvature. Experiment 4 demonstrated global processing of shape information for a range of radial frequencies and also showed that the local maximum gradient with respect to circular within an RF pattern covaries with threshold. This implies that it is this cue, or one that covaries linearly with it, that is integrated across cycles of modulation by the global processing mechanism.

Resting-State Connectivity Identifies Distinct Functional Networks in Macaque Cingulate Cortex

Subregions of the cingulate cortex represent prominent intersections in the structural networks of the primate brain. The relevance of the cingulate to the structure and dynamics of large-scale networks ultimately requires a link to functional connectivity. Here, we map fine-grained functional connectivity across the complete extent of the macaque (Macaca fascicularis) cingulate cortex and delineate subdivisions pertaining to distinct identifiable networks. In particular, we identified 4 primary networks representing the functional spectrum of the cingulate: somatomotor, attention-orienting, executive, and limbic. The cingulate nodes of these networks originated from separable subfields along the rostral-to-caudal axis and were characterized by positive and negative correlations of spontaneous blood oxygen level-dependent activity. These findings represent a critical component for understanding how the anterior and midcingulate cortices integrate and shape information processing during task performance. The connectivity patterns also suggest future electrophysiological targets that may reveal new functional representations including those involved in conflict monitoring.

The Effects of NMDA Subunit Composition on Calcium Influx and Spike Timing-Dependent Plasticity in Striatal Medium Spiny Neurons

Calcium through NMDA receptors (NMDARs) is necessary for the long-term potentiation (LTP) of synaptic strength; however, NMDARs differ in several properties that can influence the amount of calcium influx into the spine. These properties, such as sensitivity to magnesium block and conductance decay kinetics, change the receptor's response to spike timing dependent plasticity (STDP) protocols, and thereby shape synaptic integration and information processing. This study investigates the role of GluN2 subunit differences on spine calcium concentration during several STDP protocols in a model of a striatal medium spiny projection neuron (MSPN). The multi-compartment, multi-channel model exhibits firing frequency, spike width, and latency to first spike similar to current clamp data from mouse dorsal striatum MSPN. We find that NMDAR-mediated calcium is dependent on GluN2 subunit type, action potential timing, duration of somatic depolarization, and number of action potentials. Furthermore, the model demonstrates that in MSPNs, GluN2A and GluN2B control which STDP intervals allow for substantial calcium elevation in spines. The model predicts that blocking GluN2B subunits would modulate the range of intervals that cause long term potentiation. We confirmed this prediction experimentally, demonstrating that blocking GluN2B in the striatum, narrows the range of STDP intervals that cause long term potentiation. This ability of the GluN2 subunit to modulate the shape of the STDP curve could underlie the role that GluN2 subunits play in learning and development.

Eye movement patterns during the recognition of three-dimensional objects: Preferential fixation of concave surface curvature minima

This study used eye movement patterns to examine how high-level shape information is used during 3D object recognition. Eye movements were recorded while observers either actively memorized or passively viewed sets of novel objects, and then during a subsequent recognition memory task. Fixation data were contrasted against different algorithmically generated models of shape analysis based on: (1) regions of internal concave or (2) convex surface curvature discontinuity or (3) external bounding contour. The results showed a preference for fixation at regions of internal local features during both active memorization and passive viewing but also for regions of concave surface curvature during the recognition task. These findings provide new evidence supporting the special functional status of local concave discontinuities in recognition and show how studies of eye movement patterns can elucidate shape information processing in human vision.

The computational power of astrocyte mediated synaptic plasticity

Research in the last two decades has made clear that astrocytes play a crucial role in the brain beyond their functions in energy metabolism and homeostasis. Many studies have shown that astrocytes can dynamically modulate neuronal excitability and synaptic plasticity, and might participate in higher brain functions like learning and memory. With the plethora of astrocyte mediated signaling processes described in the literature today, the current challenge is to identify, which of these processes happen under what physiological condition, and how this shapes information processing and, ultimately, behavior. To answer these questions will require a combination of advanced physiological, genetical, and behavioral experiments. Additionally, mathematical modeling will prove crucial for testing predictions on the possible functions of astrocytes in neuronal networks, and to generate novel ideas as to how astrocytes can contribute to the complexity of the brain. Here, we aim to provide an outline of how astrocytes can interact with neurons. We do this by reviewing recent experimental literature on astrocyte-neuron interactions, discussing the dynamic effects of astrocytes on neuronal excitability and short- and long-term synaptic plasticity. Finally, we will outline the potential computational functions that astrocyte-neuron interactions can serve in the brain. We will discuss how astrocytes could govern metaplasticity in the brain, how they might organize the clustering of synaptic inputs, and how they could function as memory elements for neuronal activity. We conclude that astrocytes can enhance the computational power of neuronal networks in previously unexpected ways.

Crisis decision theory: Decisions in the face of negative events.

How do people respond to negative life events? Crisis decision theory combines the strengths of coping theories with research on decision making to predict the responses people choose under negative circumstances. The theory integrates literatures on coping, health behavior, and decision making, among others, into 3 stages that describe the process of responding to negative events: (a) assessing the severity of the negative event, (b) determining response options, and (c) evaluating response options. The author reviews and organizes the relevant research on factors that shape information processing at each stage and that ultimately predict decisions in the face of negative events. Finally, the author presents a critique of crisis decision theory and discusses areas for future research.