Spatiotemporal Integration Research Articles

Spatiotemporal integration for tactile localization during arm movements: a probabilistic approach

It has been shown that people make systematic errors in the localization of a brief tactile stimulus that is delivered to the index finger while they are making an arm movement. Here we modeled these spatial errors with a probabilistic approach, assuming that they follow from temporal uncertainty about the occurrence of the stimulus. In the model, this temporal uncertainty converts into a spatial likelihood about the external stimulus location, depending on arm velocity. We tested the prediction of the model that the localization errors depend on arm velocity. Participants (n = 8) were instructed to localize a tactile stimulus that was presented to their index finger while they were making either slow- or fast-targeted arm movements. Our results confirm the model's prediction that participants make larger localization errors when making faster arm movements. The model, which was used to fit the errors for both slow and fast arm movements simultaneously, accounted very well for all the characteristics of these data with temporal uncertainty in stimulus processing as the only free parameter. We conclude that spatial errors in dynamic tactile perception stem from the temporal precision with which tactile inputs are processed.

Robust shape perception of static and rotating objects revealed by spatiotemporal form integration

Robust shape perception of static and rotating objects revealed by spatiotemporal form integration

Robust shape perception of static and rotating objects revealed by spatiotemporal form integration

Robust shape perception of static and rotating objects revealed by spatiotemporal form integration

The supplementation of spatial information improves coordination

Vision plays an important role in allowing the development of coordinated movements and often acts as the dominant perceptual modality for every day movements. This visual information is often presented in the spatio-temporal domain but the specific role of spatio-temporal information has not been specifically assessed in the literature. This experiment used two visual stimuli to assess the reliance on spatio-temporal integration and the effect of supplementing spatial information to a temporal stimulus on coordination. Participants manipulated a hand held pendulum at three frequencies in coordination with these stimuli. The results revealed that the supplementation of spatial information significantly improved coordination. Interestingly, the absence of spatial information still produced good levels of coordination indicating a resilience of motor coordination to adapt to changes in the environment.

Surround Modulation Characteristics of Local Field Potential and Spiking Activity in Primary Visual Cortex of Cat

In primary visual cortex, spiking activity that evoked by stimulus confined in receptive field can be modulated by surround stimulus. This center-surround interaction is hypothesized to be the basis of visual feature integration and segregation. Spiking output has been extensively reported to be surround suppressive. However, less is known about the modulation properties of the local field potential (LFP), which generally reflects synaptic inputs. We simultaneously recorded spiking activity and LFP in the area 17 of anesthetized cats to examine and compare their modulation characteristics. When the stimulus went beyond the classical receptive field, LFP exhibited decreased power along the gamma band (30–100 Hz) in most of our recording sites. Further investigation revealed that suppression of the LFP gamma mean power (gLFP) depended on the angle between the center and surround orientations. The strongest suppression was induced when center and surround orientations were parallel. Moreover, the surround influence of the gLFP exhibited an asymmetric spatial organization. These results demonstrate that the gLFP has similar but not identical surround modulation properties, as compared to the spiking activity. The spatiotemporal integration of LFP implies that the oscillation and synchronization of local synaptic inputs may have important functions in surround modulation.

Visual Crowding at a Distance during Predictive Remapping

When we move our eyes, images of objects are displaced on the retina, yet the visual world appears stable. Oculomotor activity just prior to an eye movement contributes to perceptual stability by providing information about the predicted location of a relevant object on the retina following a saccade. It remains unclear, however, whether an object's features are represented at the remapped location. Here, we exploited the phenomenon of visual crowding to show that presaccadic remapping preserves the elementary features of objects at their predicted postsaccadic locations. Observers executed an eye movement and identified a letter probe flashed just before the saccade. Flanking stimuli were flashed around the location that would be occupied by the probe immediately following the saccade. Despite being positioned in the opposite visual field to the probe, these flankers disrupted observers' ability to identify the probe. Crucially, this "remapped crowding" interference was stronger when the flankers were visually similar to the probe than when the flanker and probe stimuli were distinct. Our findings suggest that visual processing at remapped locations is featurally dependent, providing a mechanism for achieving perceptual continuity of objects across saccades.

Trawling bats exploit an echo-acoustic ground effect

A water surface acts not only as an optic mirror but also as an acoustic mirror. Echolocation calls emitted by bats at low heights above water are reflected away from the bat, and hence the background clutter is reduced. Moreover, targets on the surface create an enhanced echo. Here, we formally quantified the effect of the surface and target height on both target detection and -discrimination in a combined laboratory and field approach with Myotis daubentonii. In a two-alternative, forced-choice paradigm, the bats had to detect a mealworm and discriminate it from an inedible dummy (20 mm PVC disc). Psychophysical performance was measured as a function of height above either smooth surfaces (water or PVC) or above a clutter surface (artificial grass). At low heights above the clutter surface (10, 20, or 35 cm), the bats' detection performance was worse than above a smooth surface. At a height of 50 cm, the surface structure had no influence on target detection. Above the clutter surface, also target discrimination was significantly impaired with decreasing target height. A detailed analysis of the bats' echolocation calls during target approach shows that above the clutter surface, the bats produce calls with significantly higher peak frequency. Flight-path reconstruction revealed that the bats attacked an target from below over water but from above over a clutter surface. These results are consistent with the hypothesis that trawling bats exploit an echo-acoustic ground effect, in terms of a spatio-temporal integration of direct reflections with indirect reflections from the water surface, to optimize prey detection and -discrimination not only for prey on the water but also for some range above.

Kalman-filter based spatio-temporal disparity integration

Vision-based applications usually have as input a continuous stream of data. Therefore, it is possible to use the information generated in previous frames to improve the analysis of the current one. In the context of video-based driver-assistance systems, objects present in a scene typically perform a smooth motion through the image sequence. By considering a motion model for the ego-vehicle, it is possible to take advantage of previously processed data when analysing the current frame.This paper presents a Kalman filter-based approach that focuses on the reduction of the uncertainty in depth estimation (via stereo-vision algorithms) by using information from the temporal and spatial domains. For each pixel in the current disparity map, we refine the estimated value using the stereo data from a neighbourhood of pixels in previous and current frames. We aim at an improvement of existing methods that use data from the temporal domain by adding extra information from the spatial domain. To show the effectiveness of the proposed method, we analyse the performance on long synthetic sequences using different stereo matching algorithms, and compare the results obtained by the previous and the suggested approach.

Spatiotemporal Reconfiguration of Large-Scale Brain Functional Networks during Propofol-Induced Loss of Consciousness

Applying graph theoretical analysis of spontaneous BOLD fluctuations in functional magnetic resonance imaging (fMRI), we investigated whole-brain functional connectivity of 11 healthy volunteers during wakefulness and propofol-induced loss of consciousness (PI-LOC). After extraction of regional fMRI time series from 110 cortical and subcortical regions, we applied a maximum overlap discrete wavelet transformation and investigated changes in the brain's intrinsic spatiotemporal organization. During PI-LOC, we observed a breakdown of subcortico-cortical and corticocortical connectivity. Decrease of connectivity was pronounced in thalamocortical connections, whereas no changes were found for connectivity within primary sensory cortices. Graph theoretical analyses revealed significant changes in the degree distribution and local organization metrics of brain functional networks during PI-LOC: compared with a random network, normalized clustering was significantly increased, as was small-worldness. Furthermore we observed a profound decline in long-range connections and a reduction in whole-brain spatiotemporal integration, supporting a topological reconfiguration during PI-LOC. Our findings shed light on the functional significance of intrinsic brain activity as measured by spontaneous BOLD signal fluctuations and help to understand propofol-induced loss of consciousness.

The neural correlates of spatiotemporal form integration in object and motion perception

The neural correlates of spatiotemporal form integration in object and motion perception

Impaired Spatial-Temporal Integration of Touch in Xenomelia (Body Integrity Identity Disorder)

Body integrity identity disorder (BIID), or xenomelia, is a failure to integrate a fully functional limb into a coherent body schema. It manifests as the desire for amputation of the particular limb below an individually stable ‘demarcation line.’ Here we show, in five individuals with xenomelia, defective temporal order judgments to two tactile stimuli, one proximal, the other distal of the demarcation line. Spatio-temporal integration, known to be mediated by the parietal lobes, was biased towards the undesired body part, apparently capturing the individual's attention in a pathologically exaggerated way. This finding supports the view of xenomelia as a parietal lobe syndrome.

Identification of ZapD as a Cell Division Factor That Promotes the Assembly of FtsZ in Escherichia coli

The tubulin homolog FtsZ forms a polymeric membrane-associated ring structure (Z ring) at midcell that establishes the site of division and provides an essential framework for the localization of a multiprotein molecular machine that promotes division in Escherichia coli. A number of regulatory proteins interact with FtsZ and modulate FtsZ assembly/disassembly processes, ensuring the spatiotemporal integrity of cytokinesis. The Z-associated proteins (ZapA, ZapB, and ZapC) belong to a group of FtsZ-regulatory proteins that exhibit functionally redundant roles in stabilizing FtsZ-ring assembly by binding and bundling polymeric FtsZ at midcell. In this study, we report the identification of ZapD (YacF) as a member of the E. coli midcell division machinery. Genetics and cell biological evidence indicate that ZapD requires FtsZ but not other downstream division proteins for localizing to midcell, where it promotes FtsZ-ring assembly via molecular mechanisms that overlap with ZapA. Biochemical evidence indicates that ZapD directly interacts with FtsZ and promotes bundling of FtsZ protofilaments. Similarly to ZapA, ZapB, and ZapC, ZapD is dispensable for division and therefore belongs to the growing group of FtsZ-associated proteins in E. coli that aid in the overall fitness of the division process.

Postdictive Modulation of Visual Orientation

The present study investigated how visual orientation is modulated by subsequent orientation inputs. Observers were presented a near-vertical Gabor patch as a target, followed by a left- or right-tilted second Gabor patch as a distracter in the spatial vicinity of the target. The task of the observers was to judge whether the target was right- or left-tilted (Experiment 1) or whether the target was vertical or not (Supplementary experiment). The judgment was biased toward the orientation of the distracter (the postdictive modulation of visual orientation). The judgment bias peaked when the target and distracter were temporally separated by 100 ms, indicating a specific temporal mechanism for this phenomenon. However, when the visibility of the distracter was reduced via backward masking, the judgment bias disappeared. On the other hand, the low-visibility distracter could still cause a simultaneous orientation contrast, indicating that the distracter orientation is still processed in the visual system (Experiment 2). Our results suggest that the postdictive modulation of visual orientation stems from spatiotemporal integration of visual orientation on the basis of a slow feature matching process.

Instrumentation of a compact random-access photostimulator based on acousto-optic deflectors

Recently developed optogenetics provides a fast, non-invasive, and efficient method for cell activation. However, it is difficult for the optical stimulators used for optogenetics to realize selective multi-site fast activation. In this paper, we developed a random-access photostimulator based on a pair of perpendicularly oriented acousto-optic deflectors. Precise laser targeting in the x-y plane was verified, and the lateral spatial resolution of laser intensity after the objective was measured as ∼1.38 μm. Photostimulaton of ChETA-expressing astrocytes induced reliable inward currents only if the laser beam was directed onto the targeted cell. In the ChR2-expresing neuron, multiple locations along two dendrites were stimulated, and spatiotemporal integration was observed in the soma with fast multi-site activation. These results demonstrated that this random-access photostimulator would be a powerful tool for selective multi-site fast activation. The compact and modular design of this photostimulator makes it easily integrated with different commercial microscopes, and thus widely popularized in many laboratories.

Mental visualization of objects from cross-sectional images

We extended the classic anorthoscopic viewing procedure to test a model of visualization of 3D structures from 2D cross-sections. Four experiments were conducted to examine key processes described in the model, localizing cross-sections within a common frame of reference and spatiotemporal integration of cross sections into a hierarchical object representation. Participants used a hand-held device to reveal a hidden object as a sequence of cross-sectional images. The process of localization was manipulated by contrasting two displays, in situ vs. ex situ, which differed in whether cross sections were presented at their source locations or displaced to a remote screen. The process of integration was manipulated by varying the structural complexity of target objects and their components. Experiments 1 and 2 demonstrated visualization of 2D and 3D line-segment objects and verified predictions about display and complexity effects. In Experiments 3 and 4, the visualized forms were familiar letters and numbers. Errors and orientation effects showed that displacing cross-sectional images to a remote display (ex situ viewing) impeded the ability to determine spatial relationships among pattern components, a failure of integration at the object level.

Spatio-temporal Integration Method for Shop and Office Data with Location Information and Application for Urban and Regional Analysis

Spatio-temporal Integration Method for Shop and Office Data with Location Information and Application for Urban and Regional Analysis

Motion-based predictive coding is sufficient to solve the aperture problem

It is still unclear how information collected locally by low-level sensory neurons may give rise to a coherent global percept. This is well demonstrated in the aperture problem both in visual or haptic senses. Experimental findings on its biological solution in area MT show that local motion measures are integrated to see the dynamical emergence of global motion information [1]. We develop a theory of spatio-temporal integration defined as implementing motion-based predictive coding. This takes the form of an anisotropic, context-dependent diffusion of local information [2]. Here, we test this functional model for the aperture problem in the visual and haptic low-level sensory areas. In our model, spatial and motion information is represented in a probabilistic framework. Information is pooled using a Markov chain formulation, merging current information and measurement likelihood thanks to a prior on motion transition. This prior is defined so that it is adapted to smooth trajectories such as are observed in natural environments.This dynamical system favors temporally coherent features. Differently to neural approximations [3], we use a particle filtering method to implement this functional model. This generalizes Kalman filtering approaches that were used previously by allowing to represent non-gaussian and multimodal distributions. We observe the emergence of mechanisms that reflect observations made at psychophysical and behavioral levels. First, the dynamical system shows the emergence of the solution to the aperture problem and show dependence to line’s length [4]. Then,when presented with an object with a regular translation, the dynamical system grabs itsmotion independently of its shape and exhibits motion extrapolation. This shows that prediction is sufficient for the dynamical build-up of information from a local to a global scale. More generally it may give insights in the role of spatio-temporal integration on neural dynamics in the emergence of properties that are accredited to low-level sensory computations.

SH3BP1, an Exocyst-Associated RhoGAP, Inactivates Rac1 at the Front to Drive Cell Motility

The coordination of the several pathways involved in cell motility is poorly understood. Here, we identify SH3BP1, belonging to the RhoGAP family, as a partner of the exocyst complex and establish a physical and functional link between two motility-driving pathways, the Ral/exocyst and Rac signaling pathways. We show that SH3BP1 localizes together with the exocyst to the leading edge of motile cells and that SH3BP1 regulates cell migration via its GAP activity upon Rac1. SH3BP1 loss of function induces abnormally high Rac1 activity at the front, as visualized by in vivo biosensors, and disorganized and instable protrusions, as revealed by cell morphodynamics analysis. Consistently, constitutively active Rac1 mimics the phenotype of SH3BP1 depletion: slow migration and aberrant cell morphodynamics. Our finding that SH3BP1 downregulates Rac1 at the motile-cell front indicates that Rac1 inactivation in this location, as well as its activation by GEF proteins, is a fundamental requirement for cell motility.

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L.

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.

The Drosophila L1CAM homolog Neuroglian signals through distinct pathways to control different aspects of mushroom body axon development

The spatiotemporal integration of adhesion and signaling during neuritogenesis is an important prerequisite for the establishment of neuronal networks in the developing brain. In this study, we describe the role of the L1-type CAM Neuroglian protein (NRG) in different steps of Drosophila mushroom body (MB) neuron axonogenesis. Selective axon bundling in the peduncle requires both the extracellular and the intracellular domain of NRG. We uncover a novel role for the ZO-1 homolog Polychaetoid (PYD) in axon branching and in sister branch outgrowth and guidance downstream of the neuron-specific isoform NRG-180. Furthermore, genetic analyses show that the role of NRG in different aspects of MB axonal development not only involves PYD, but also TRIO, SEMA-1A and RAC1.