Spatially Aligned Research Articles

Self-Supervised Learning across the Spectrum

Satellite image time series (SITS) segmentation is crucial for many applications, like environmental monitoring, land cover mapping, and agricultural crop type classification. However, training models for SITS segmentation remains a challenging task due to the lack of abundant training data, which requires fine-grained annotation. We propose S4, a new self-supervised pretraining approach that significantly reduces the requirement for labeled training data by utilizing two key insights of satellite imagery: (a) Satellites capture images in different parts of the spectrum, such as radio frequencies and visible frequencies. (b) Satellite imagery is geo-registered, allowing for fine-grained spatial alignment. We use these insights to formulate pretraining tasks in S4. To the best of our knowledge, S4 is the first multimodal and temporal approach for SITS segmentation. S4’s novelty stems from leveraging multiple properties required for SITS self-supervision: (1) multiple modalities, (2) temporal information, and (3) pixel-level feature extraction. We also curate m2s2-SITS, a large-scale dataset of unlabeled, spatially aligned, multimodal, and geographic-specific SITS that serves as representative pretraining data for S4. Finally, we evaluate S4 on multiple SITS segmentation datasets and demonstrate its efficacy against competing baselines while using limited labeled data. Through a series of extensive comparisons and ablation studies, we demonstrate S4’s ability as an effective feature extractor for downstream semantic segmentation.

Synchronized affect in shared experiences strengthens social connection

People structure their days to experience events with others. We gather to eat meals, watch TV, and attend concerts together. What constitutes a shared experience and how does it manifest in dyadic behavior? The present study investigates how shared experiences—measured through emotional, motoric, physiological, and cognitive alignment—promote social bonding. We recorded the facial expressions and electrodermal activity (EDA) of participants as they watched four episodes of a TV show for a total of 4 h with another participant. Participants displayed temporally synchronized and spatially aligned emotional facial expressions and the degree of synchronization predicted the self-reported social connection ratings between viewing partners. We observed a similar pattern of results for dyadic physiological synchrony measured via EDA and their cognitive impressions of the characters. All four of these factors, temporal synchrony of positive facial expressions, spatial alignment of expressions, EDA synchrony, and character impression similarity, contributed to a latent factor of a shared experience that predicted social connection. Our findings suggest that the development of interpersonal affiliations in shared experiences emerges from shared affective experiences comprising synchronous processes and demonstrate that these complex interpersonal processes can be studied in a holistic and multi-modal framework leveraging naturalistic experimental designs.

Electrospun gelatin-based biomimetic scaffold with spatially aligned and three-layer architectures for vascular tissue engineering

The spatial cellular alignment and multi-layer structure are vitally important for the physiological functions of natural blood vessels. However, the two features are difficult to be constructed in one scaffold simultaneously, especially in the small-diameter vascular scaffold. Here we report a general strategy to construct a gelatin-based biomimetic three-layer vascular scaffold with spatial alignment features mimicking the natural structure of blood vessels. By using a sequential electrospinning strategy combined with folding and rolling manipulation, a three-layer vascular scaffold with inner and middle layers spatially perpendicular to each other was obtained. The special features of this scaffold could fully mimic the natural multi-layer structures of blood vessels and also possess great potential for spatial arrangement guidance of corresponding cells in blood vessels.

Multi-Atlas Segmentation and Spatial Alignment of the Human Embryo in First Trimester 3D Ultrasound

Segmentation and spatial alignment of ultrasound imaging data acquired in the in first trimester are crucial for monitoring early human embryonic growth and development throughout this crucial period of life. Current approaches are either manual or semi-automatic and are therefore very time-consuming and prone to errors. To automate these tasks, we propose a multi-atlas framework for automatic segmentation and spatial alignment of the embryo using deep learning with minimal supervision. Our framework learns to register the embryo to an atlas, which consists of the ultrasound images acquired at a range of gestational ages, segmented and spatially aligned to a predefined standard orientation. From this, we can derive the segmentation of the embryo and put the embryo in standard orientation. Ultrasound images acquired at 8+0 till 12+6 weeks gestational age were used and eight pregnancies were selected as atlas images. We evaluated different fusion strategies to incorporate multiple atlases: 1) training the framework using atlas images from a single subject, 2) training the framework with data of all available atlases and 3) ensembling of the frameworks trained per subject. To evaluate the performance, we calculated the Dice score over the test set. We found that training the framework using all available atlases outperformed ensembling and gave similar results compared to the best of all frameworks trained on a single subject. Furthermore, we found that selecting images from the four atlases closest in gestational age out of all available atlases, regardless of the individual quality, gave the best results with a median Dice score of $0.72$. We conclude that our framework can accurately segment and spatially align the embryo in first trimester 3D ultrasound images and is robust for the variation in quality that existed in the available atlases. Our code is publicly available at: <a href='https://gitlab.com/radiology/prenatal-image-analysis/multi-atlas-seg-reg'>https://gitlab.com/radiology/prenatal-image-analysis/multi-atlas-seg-reg</a>

Spatial alignment between faces and voices improves selective attention to audio-visual speech.

The ability to see a talker's face improves speech intelligibility in noise, provided that the auditory and visual speech signals are approximately aligned in time. However, the importance of spatial alignment between corresponding faces and voices remains unresolved, particularly in multi-talker environments. In a series of online experiments, we investigated this using a task that required participants to selectively attend a target talker in noise while ignoring a distractor talker. In experiment 1, we found improved task performance when the talkers' faces were visible, but only when corresponding faces and voices were presented in the same hemifield (spatially aligned). In experiment 2, we tested for possible influences of eye position on this result. In auditory-only conditions, directing gaze toward the distractor voice reduced performance, but this effect could not fully explain the cost of audio-visual (AV) spatial misalignment. Lowering the signal-to-noise ratio (SNR) of the speech from +4 to -4 dB increased the magnitude of the AV spatial alignment effect (experiment 3), but accurate closed-set lipreading caused a floor effect that influenced results at lower SNRs (experiment 4). Taken together, these results demonstrate that spatial alignment between faces and voices contributes to the ability to selectively attend AV speech.

Automated segmentation of knee articular cartilage: Joint deep and hand-crafted learning-based framework using diffeomorphic mapping

Segmentation of knee articular cartilage tissue (ACT) from 3D magnetic resonance images (MRIs) is a fundamental task in assessing knee osteoarthritis (KOA). However, automated ACT segmentation of knee cartilage is complicated by (1) the variability of pathological structures in terms of shape, size, spatial resolution and (2) the uncertainties in delineating inter- and intra-cartilage boundaries (possibly touching inter-cartilage surfaces, intensity inhomogeneity, cartilage loss due to disease progression). To address these problems, we propose a novel joint deep and hand-crafted learning-based (JD-HCl) framework. The fully automated segmentation pipeline is a combination of three main steps: 3D convolutional neural networks (CNNs), diffeomorphic mapping, and a conventional hand-crafted feature-based classification model. Firstly, the initial segmentation of knee ACT was drawn from preprocessed knee MRIs using 3D U-Net. Secondly, the spatial alignment in the image domain was carried out using diffeomorphic image registration derived from an estimate of the anatomical correspondences between the subjects and population-specific template. Finally, a tissue-specific hand-crafted feature set was extracted from the spatially aligned pre-segmented ACT region and combined with the semantic context priors obtained from 3D CNN model to develop the second-stage learning model. The proposed method was evaluated with two publicly available Osteoarthritis Initiative (OAI) datasets and one in-house MRI sequences from the Alfred hospital, Melbourne, Australia. The proposed JD-HCl framework produced strong Dice similarity coefficient (DSC), ranging between 97.4% and 98.5% (95% confidence interval) for all cartilage compartments at baseline to 97.2% and 98.5% (the 1-year follow-up) for OAI(-Imorphics) dataset, and 89.3% and 94.6% for OAI-ZIB validation dataset, respectively. Average correlations of cartilage volumes between manual and automatic segmentations were 0.9 and 0.83 for OAI-ZIB dataset, respectively, and 0.975, 0.995, and 0.99 for OAI(-Imorphics) validation datasets, respectively. In longitudinal studies, accurate segmentation of knee ACT using the proposed method produces reproducible cartilage volume, thickness measurements valuable for the study of KOA progression.

GPRInvNet: Deep Learning-Based Ground-Penetrating Radar Data Inversion for Tunnel Linings

A DNN architecture referred to as GPRInvNet was proposed to tackle the challenges of mapping the ground-penetrating radar (GPR) B-Scan data to complex permittivity maps of subsurface structures. The GPRInvNet consisted of a trace-to-trace encoder and a decoder. It was specially designed to take into account the characteristics of GPR inversion when faced with complex GPR B-Scan data, as well as addressing the spatial alignment issues between time-series B-Scan data and spatial permittivity maps. It displayed the ability to fuse features from several adjacent traces on the B-Scan data to enhance each trace, and then further condense the features of each trace separately. As a result, the sensitive zones on the permittivity maps spatially aligned to the enhanced trace could be reconstructed accurately. The GPRInvNet has been utilized to reconstruct the permittivity map of tunnel linings. A diverse range of dielectric models of tunnel linings containing complex defects has been reconstructed using GPRInvNet. The results have demonstrated that the GPRInvNet is capable of effectively reconstructing complex tunnel lining defects with clear boundaries. Comparative results with existing baseline methods also demonstrated the superiority of the GPRInvNet. For the purpose of generalizing the GPRInvNet to real GPR data, some background noise patches recorded from practical model testing were integrated into the synthetic GPR data to retrain the GPRInvNet. The model testing has been conducted for validation, and experimental results revealed that the GPRInvNet had also achieved satisfactory results with regard to the real data.

Audio-visual spatial alignment improves integration in the presence of a competing audio-visual stimulus

In order to parse the world around us, we must constantly determine which sensory inputs arise from the same physical source and should therefore be perceptually integrated. Temporal coherence between auditory and visual stimuli drives audio-visual (AV) integration, but the role played by AV spatial alignment is less well understood. Here, we manipulated AV spatial alignment and collected electroencephalography (EEG) data while human subjects performed a free-field variant of the “pip and pop” AV search task. In this paradigm, visual search is aided by a spatially uninformative auditory tone, the onsets of which are synchronized to changes in the visual target. In Experiment 1, tones were either spatially aligned or spatially misaligned with the visual display. Regardless of AV spatial alignment, we replicated the key pip and pop result of improved AV search times. Mirroring the behavioral results, we found an enhancement of early event-related potentials (ERPs), particularly the auditory N1 component, in both AV conditions. We demonstrate that both top-down and bottom-up attention contribute to these N1 enhancements. In Experiment 2, we tested whether spatial alignment influences AV integration in a more challenging context with competing multisensory stimuli. An AV foil was added that visually resembled the target and was synchronized to its own stream of synchronous tones. The visual components of the AV target and AV foil occurred in opposite hemifields; the two auditory components were also in opposite hemifields and were either spatially aligned or spatially misaligned with the visual components to which they were synchronized. Search was fastest when the auditory and visual components of the AV target (and the foil) were spatially aligned. Attention modulated ERPs in both spatial conditions, but importantly, the scalp topography of early evoked responses shifted only when stimulus components were spatially aligned, signaling the recruitment of different neural generators likely related to multisensory integration. These results suggest that AV integration depends on AV spatial alignment when stimuli in both modalities compete for selective integration, a common scenario in real-world perception.

Left hemispatial neglect and overt orienting in naturalistic conditions: Role of high-level and stimulus-driven signals

Deficits of visuospatial orienting in brain-damaged patients affected by hemispatial neglect have been extensively investigated. Nonetheless, spontaneous spatial orienting in naturalistic conditions is still poorly understood. Here, we investigated the role played by top-down and stimulus-driven signals in overt spatial orienting of neglect patients during free-viewing of short videos portraying everyday life situations. In Experiment 1, we assessed orienting when meaningful visual events competed on the left and right side of space, and tested whether sensory salience on the two sides biased orienting. In Experiment 2, we examined whether the spatial alignment of visual and auditory signals modulates orienting. The results of Experiment 1 showed that in neglect patients severe deficits in contralesional orienting were restricted to viewing conditions with bilateral visual events competing for attentional capture. In contrast, orienting towards the contralesional side was largely spared when the videos contained a single event on the left side. In neglect patients the processing of stimulus-driven salience was relatively spared and helped orienting towards the left side when multiple events were present. Experiment 2 showed that sounds spatially aligned with visual events on the left side improved orienting towards the otherwise neglected hemispace. Anatomical scans indicated that neglect patients suffered grey and white matter damages primarily in the ventral frontoparietal cortex. This suggests that the improvement of contralesional orienting associated with visual salience and audiovisual spatial alignment may be due to processing in the relatively intact dorsal frontoparietal areas. Our data show that in naturalistic environments, the presence of multiple meaningful events is a major determinant of spatial orienting deficits in neglect patients, whereas the salience of visual signals and the spatial alignment between auditory and visual signals can counteract spatial orienting deficits. These results open new perspectives to develop novel rehabilitation strategies based on the use of naturalistic stimuli.

The haptic and the visual flash-lag effect and the role of flash characteristics.

When a short flash occurs in spatial alignment with a moving object, the moving object is seen ahead the stationary one. Similar to this visual “flash-lag effect” (FLE) it has been recently observed for the haptic sense that participants judge a moving hand to be ahead a stationary hand when judged at the moment of a short vibration (“haptic flash”) that is applied when the two hands are spatially aligned. We further investigated the haptic FLE. First, we compared participants’ performance in two isosensory visual or haptic conditions, in which moving object and flash were presented only in a single modality (visual: sphere and short color change, haptic: hand and vibration), and two bisensory conditions, in which the moving object was presented in both modalities (hand aligned with visible sphere), but the flash was presented only visually or only haptically. The experiment aimed to disentangle contributions of the flash’s and the objects’ modalities to the FLEs in haptics versus vision. We observed a FLE when the flash was visually displayed, both when the moving object was visual and visuo-haptic. Because the position of a visual flash, but not of an analogue haptic flash, is misjudged relative to a same visuo-haptic moving object, the difference between visual and haptic conditions can be fully attributed to characteristics of the flash. The second experiment confirmed that a haptic FLE can be observed depending on flash characteristics: the FLE increases with decreasing intensity of the flash (slightly modulated by flash duration), which had been previously observed for vision. These findings underline the high relevance of flash characteristics in different senses, and thus fit well with the temporal-sampling framework, where the flash triggers a high-level, supra-modal process of position judgement, the time point of which further depends on the processing time of the flash.

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Age, metallicity and spatial distribution of globular clusters (GCs) provide a powerful tool to reconstruct major star-formation episodes in galaxies. IKN is a faint dwarf spheroidal (dSph) in the M81 group of galaxies. It contains five old GCs, which makes it the galaxy with the highest known specific frequency (SN=126). We estimate the photometric age, metallicity and spatial distribution of the poorly studied IKN GCs. We search SDSS for GC candidates beyond the HST field of view, which covers half of IKN. To break the age-metallicity degeneracy in the V-I colour we use WHT/LIRIS Ks-band photometry and derive photometric ages and metallicities by comparison with SSP models in the V,I,Ks colour space. IKN GCs' VIKs colours are consistent with old ages ($\geq\!8$ Gyr) and a metallicity distribution with a higher mean than typical for such a dSph ([Fe/H$]\!\simeq\!-1.4_{-0.2}^{+0.6}$ dex). Their photometric masses range ($0.5 <{\cal M_{\rm GC}}<4\times10^5M_\odot$) implies a high mass ratio between GCs and field stars, of $10.6\%$. Mixture model analysis of the RGB field stars' metallicity suggests that 72\% of the stars may have formed together with the GCs. Using the most massive GC-SFR relation we calculate a SFR of $\sim\!10M_\odot/$yr during its formation epoch. We note that the more massive GCs are closer to the galaxy photometric centre. IKN GCs also appear spatially aligned along a line close to the IKN major-axis and nearly orthogonal to the plane of spatial distribution of galaxies in the M81 group. We identify one new IKN GC candidate based on colour and PSF analysis of the SDSS data. The evidence towards i) broad and high metallicity distribution of the field IKN RGB stars and its GCs, ii) high fraction and iii), spatial alignment of IKN GCs, supports a scenario for tidally triggered complex IKN's SFH in the context of interactions with galaxies in the M81 group.

Real-Time Rotation Estimation Using Histograms of Oriented Gradients

This paper focuses on real-time rotation estimation for model-based automated visual inspection. In the case of model-based inspection, spatial alignment is essential to distinguish visual defects from normal appearance variations. Defects are detected by comparing the inspected object with its spatially aligned ideal reference model. Rotation estimation is crucial for the inspection of rotationally symmetric objects where mechanical manipulation is unable to ensure the correct object rotation. We propose a novel method for in-plane rotation estimation. Rotation is estimated with an ensemble of nearest-neighbor estimators. Each estimator contains a spatially local representation of an object in a feature space for all rotation angles and is constructed with a semi-supervised self-training approach from a set of unlabeled training images. An individual representation in a feature space is obtained by calculating the Histograms of Oriented Gradients (HOG) over a spatially local region. Each estimator votes separately for the estimated angle; all votes are weighted and accumulated. The final estimation is the angle with the most votes. The method was evaluated on several datasets of pharmaceutical tablets varying in size, shape, and color. The results show that the proposed method is superior in robustness with comparable speed and accuracy to previously proposed methods for rotation estimation of pharmaceutical tablets. Furthermore, all evaluations were performed with the same set of parameters, which implies that the method requires minimal human intervention. Despite the evaluation focused on pharmaceutical tablets, we consider the method useful for any application that requires robust real-time in-plane rotation estimation.

Impact of the spatial congruence of redundant targets on within-modal and cross-modal integration

Although the topic of sensory integration has raised increasing interest, the differing behavioral outcome of combining unisensory versus multisensory inputs has surprisingly only been scarcely investigated. In the present experiment, observers were required to respond as fast as possible to (1) lateralized visual or tactile targets presented alone, (2) double stimulation within the same modality or (3) double stimulation across modalities. Each combination was either delivered within the same hemispace (spatially aligned) or in different hemispaces (spatially misaligned). Results show that the redundancy gains (RG) obtained from the cross-modal conditions were far greater than those obtained from combinations of two visual or two tactile targets. Consistently, we observed that the reaction time distributions of cross-modal targets, but not those of within-modal targets, surpass the predicted reaction time distribution based on the summed probability distributions of each constituent stimulus presented alone. Moreover, we found that the spatial alignment of the targets did not influence the RG obtained in cross-modal conditions, whereas within-modal stimuli produced a greater RG when the targets where delivered in separate hemispaces. These results suggest that within-modal and cross-modal integration are not only distinguishable by the amount of facilitation they produce, but also by the spatial configuration under which this facilitation occurs. Our study strongly supports the notion that estimates of the same event that are more independent produce enhanced integrative gains.

Auditory–somatosensory multisensory interactions in humans: Dissociating detection and spatial discrimination

Simple reaction times (RTs) to auditory–somatosensory (AS) multisensory stimuli are facilitated over their unisensory counterparts both when stimuli are delivered to the same location and when separated. In two experiments we addressed the possibility that top-down and/or task-related influences can dynamically impact the spatial representations mediating these effects and the extent to which multisensory facilitation will be observed. Participants performed a simple detection task in response to auditory, somatosensory, or simultaneous AS stimuli that in turn were either spatially aligned or misaligned by lateralizing the stimuli. Additionally, we also informed the participants that they would be retrogradely queried (one-third of trials) regarding the side where a given stimulus in a given sensory modality was presented. In this way, we sought to have participants attending to all possible spatial locations and sensory modalities, while nonetheless having them perform a simple detection task. Experiment 1 provided no cues prior to stimulus delivery. Experiment 2 included spatially uninformative cues (50% of trials). In both experiments, multisensory conditions significantly facilitated detection RTs with no evidence for differences according to spatial alignment (though general benefits of cuing were observed in Experiment 2). Facilitated detection occurs even when attending to spatial information. Performance with probes, quantified using sensitivity (d′), was impaired following multisensory trials in general and significantly more so following misaligned multisensory trials. This indicates that spatial information is not available, despite being task-relevant. The collective results support a model wherein early AS interactions may result in a loss of spatial acuity for unisensory information.

Possible EIT-like effects in strong-field photo-dissociation of carbon disulphide

CS 2 molecules are spatially aligned upon irradiation by intense (1–100 TW cm −2), 35 ps pulses of 512 nm or 355 nm light. When both colours are simultaneously present, spatial alignment disappears. We draw analogy with weak-field illumination of an atom by two colours wherein EIT (electromagnetically induced transparency) inhibits absorption by virtue of dipoles not being induced in two-colour fields. In the strong-field scenario, molecular alignment is a consequence of a dipole being induced in the direction of the applied electric field. It follows, therefore, that when dipoles are not induced, no spatial alignment is to be expected.

Crossmodal Integration in the Primate Superior Colliculus Underlying the Preparation and Initiation of Saccadic Eye Movements

Saccades to combined audiovisual stimuli often have reduced saccadic reaction times (SRTs) compared with those to unimodal stimuli. Neurons in the intermediate/deep layers of the superior colliculus (dSC) are capable of integrating converging sensory inputs to influence the time to saccade initiation. To identify how neural processing in the dSC contributes to reducing SRTs to audiovisual stimuli, we recorded activity from dSC neurons while monkeys generated saccades to visual or audiovisual stimuli. To evoke crossmodal interactions of varying strength, we used auditory and visual stimuli of different intensities, presented either in spatial alignment or to opposite hemifields. Spatially aligned audiovisual stimuli evoked the shortest SRTs. In the case of low-intensity stimuli, the response to the auditory component of the aligned audiovisual target increased the activity preceding the response to the visual component, accelerating the onset of the visual response and facilitating the generation of shorter-latency saccades. In the case of high-intensity stimuli, the auditory and visual responses occurred much closer together in time and so there was little opportunity for the auditory stimulus to influence previsual activity. Instead, the reduction in SRT for high-intensity, aligned audiovisual stimuli was correlated with increased premotor activity (activity after visual burst but preceding saccade-aligned burst). These data provide a link between changes in neural activity related to stimulus modality with changes in behavior. They further demonstrate how crossmodal interactions are not limited to the initial sensory activity but can also influence premotor activity in the SC.

D 22+ dication as a probe of spatial alignment of D 2 molecules in intense laser light

The dissociative double ionization of D 2 has been studied in a 532 nm, linearly polarized laser field with intensities in the range 10 13–10 14 W cm −2. The laser-field-induced dipole moment gives rise to a torque on D 2 molecules that tends to dynamically align the D–D axis parallel to the laser polarization vector. From measurements of the dependence on polarization angle of the kinetic energy of the D + + D + fragment pairs a simple method, which may be of wide applicability, is developed that yields semiquantitative information on the fraction of molecules that are spatially aligned by the linearly polarized laser field.

Angle-resolved covariance mapping of spatially-aligned in an intense picosecond laser field

Angle-resolved covariance mapping has been applied to measure the angular distributions of - and - ion pairs resulting from double ionization of using picosecond-duration, linearly-polarized laser pulses of intensity is spatially aligned along the laser polarization vector much more efficiently than . The field-induced dipole moment of the dication is calculated to be 21% more than that of the cation. The following sequence of events is inferred upon immersion of in the intense field: ionization and double ionization spatial alignment dissociation.

Observing and imitating the formation of object classes during the second year of life.

The developmental origins of overt object classification are still poorly understood, but one factor that may be informative and facilitative of classification during the second year is observing adults group similar objects. A pretest-posttest design with modeling and control groups was used to assess the impact of modeling on deferred imitation of groupings based on object similarity. Children at three ages (12, 18, and 24 months) observed an adult produce class groupings and alignments of objects. By 18 and 24 months, there was significant deferred imitation of object groupings. There was virtually no effect at 12 months. Moreover, only at 24 months were classified sets spatially aligned. The results indicate that observing adult classification will at least facilitate object grouping during the latter part of the second year, and that it may promote the use of spatial alignments as organizing devices or as modes of depicting object classes.

Prismatic displacement of vision induces transient changes in the timing of eye-hand coordination.

Eye-hand coordination was investigated during a task of finger pointing toward visual targets viewed through wedge prisms. Hand and eye latencies and movement times were identical during the control condition and at the end of prism exposure. A temporal reorganization of eye and hand movements was observed during the course of adaptation. During the earlier stage of prism exposure, the time gap between the end of the eye saccade and the onset of hand movement was increased from a control time of 23 to 68 msec. This suggests that a time-consuming process occurred during the early prism-exposure period. The evolution of this time gap was correlated with the evolution of pointing errors during the early stage of prism exposure, in such a way that both measures increased at the onset of prism exposure and decreased almost back to control values within about 10 trials. However, spatial error was not entirely corrected, even late in prism exposure when the temporal organization of eye and hand had returned to baseline. These data suggest that two different adaptive mechanisms were at work: a rather short-term mechanism, involved in normal coordination of spatially aligned eye and hand systems, and a long-term mechanism, responsible for remapping spatially misaligned systems. The former mechanism can be strategically employed to quickly optimize accuracy in a situation involving misalignment, but completely adaptive behavior must await the slower-acting latter mechanism to achieve long-term spatial alignment.