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At least 1,081 records · Page 60Linked to original sources
PubMed2003

Reduced influence of the ipsilateral ear on spatial tuning of auditory neurons in the albino superior colliculus: a knock-on effect of anomalies of the acoustic chiasm?

Auditory brainstem abnormalities affecting decussation patterns and nuclei involved in the acoustic chiasm exist in a variety of albino mammals, suggesting that binaural processes underlying spatial hearing may be disrupted in these mutants. To evaluate this we have compared the contribution of the two ears in albino and normally pigmented guinea pigs to the spatial tuning of auditory neurons in the deep layers of the superior colliculus (SC). Broadband noise stimuli at threshold and at suprathreshold intensities were presented from different azimuthal loudspeaker locations under free-field anechoic conditions, and auditory receptive fields were plotted before, during and after occluding the ipsilateral ear. We show that the deep layers of the albino SC contain a map of contralateral auditory azimuth along its anteroposterior axis, which is aligned with the visual map in the superficial layers above, just as in normal animals. We also show that threshold spatial responses are elicited only via the contralateral ear and at similar stimulus intensities (mean approximately 30 dB SPL) in the two pigmentation phenotypes. The mechanisms that maintain spatial tuning at sound intensities of 10-40 dB above threshold, however, differ markedly in these animals. Plugging the ipsilateral ear in normal guinea pigs caused significant expansions of their auditory receptive fields and loss of directional tuning, but in the albinos occlusion had little effect on these spatial properties. The results suggest that while spatial selectivity for relatively loud sounds among SC neurons is normally maintained via the binaural combination of contralateral excitatory drive and ipsilateral inhibition, it is achieved in albinos almost exclusively by monaural input from the contralateral ear. This finding is consistent with an excessive contralateral ear dominance of higher levels of the albino auditory system caused by anomalies of their acoustic chiasm, analogous to the monocular dominance of the visual system that results from excessive axon crossing at the optic chiasm in these animals.

Animals↗
PubMed2003

Spatial representation of corticofugal input in the inferior colliculus: a multicontact silicon probe approach.

The inferior colliculus (IC) is a well-established target of descending projections from the auditory cortex (AC). However, our understanding of these pathways has been limited by an incomplete picture of their functional influence within the three-dimensional space of the IC. Our goal was to study the properties and spatial representation of corticofugal input in the IC of guinea pigs with a high degree of spatial resolution. We systematically mapped neural activity in the IC using two types of silicon substrate probes that allow for simultaneous recording at multiple neural sites. One probe provided a high resolution in the dorsal-ventral plane and the other provided spatial resolution in the medial-lateral plane. Electrical stimulation of the ipsilateral AC produced excitatory responses in the IC with thresholds usually below 5-10 microA. First spike latencies were predominantly in the 6-20 ms range, although latencies from 3-5 ms were also observed. Broadly distributed unimodal spike patterns with modal latencies greater than 30 ms were occasionally seen. The excitatory responses to cortical stimulation were mostly unimodal and occasionally bimodal with a wide range of spike distribution patterns and response durations. Excitation was often followed by suppression of spontaneous activity. Suppression of acoustic responses was observed even when there was little or no response to electrical stimulation, suggesting spatial-temporal integration. A few of the responding neurons showed purely inhibitory responses to electrical stimulation, suggesting that there are disynaptic routes of corticocollicular inhibition. Detailed spatial mapping revealed that the response patterns and their durations had a characteristic spatial distribution in the IC.

Action Potentials↗
PubMed2004

Neural mechanisms of spatial stimulus-response compatibility: the effect of crossed-hand position.

Previous psychological experiments have indicated the existence of a visual-proprioceptive interaction in spatial stimulus-response compatibility (SSRC) tasks, but there is little specific information on the neural basis of such interaction in humans. Using functional magnetic resonance imaging (fMRI), we compared the neural activity associated with two different aspects of spatial coding: the coding of the "internal" spatial position of motor-response effectors (i.e., the position of body parts) as obtained through proprioception, and the coding of "external" positions, i.e., the positions of visual stimuli. A 2 x 2 factorial design was used to investigate the spatial compatibility (incompatible versus compatible) between a visual stimulus and hand position (crossed versus uncrossed). The subjects were instructed to respond to stimuli presented to the right or left visual field with either the ipsilateral (compatible condition) or the contralateral hand (incompatible condition). The incompatible condition produced stronger activation in the bilateral superior parietal lobule, inferior parietal lobule, and bilateral superior frontal gyrus than the compatible condition. The crossed-hand condition produced stronger activation in the bilateral precentral gyrus, superior frontal gyrus, superior parietal lobule, and superior temporal gyrus than the uncrossed-hand condition. These results suggest that activity in the frontal-parietal regions is related to two functions: (1) representation of the visual stimulus-motor response spatial configuration in an SSRC task, and (2) integration between external visual and internal proprioceptive sensory information. The activation in the superior temporal gyrus was not affected by the visual stimulus-motor response spatial configuration in an SSRC task; rather, it was affected by the crossed-hand posture. Thus, it seems to be related to representing internal proprioceptive sensory information necessary to carry out motor actions.

Adult↗
PubMed2004

The effect of postural stability and spatial orientation of the upper limbs on interlimb coordination.

It has recently been reported that the spatial orientation of two moving limbs has a determining influence on the relative accuracy and stability of coordination patterns. The purpose of the present experiments was to test perceptual and neuromuscular explanations of these spatial orientation effects. Experiment 1 was an initial test of the hypotheses and an extension of a previous study [Lee et al. (2002) Exp Brain Res 146:205-212] that required participants to coordinate inphase and antiphase movement patterns in four spatial orientations: two symmetric orientations (90 degrees and 180 degrees separation between the limbs) and two asymmetric orientations (90 degrees and 135 degrees separation between the limbs). Results of Experiment 1 suggest that the symmetry of movement may be a key factor influencing spatial orientation effects observed during interlimb coordination. In Experiment 2, participants again performed inphase and antiphase movement patterns in symmetric and asymmetric spatial orientations. However, one-half of the participants in Experiment 2 were provided with mechanical constraints during the performance of the desired coordination patterns. The mechanical constraints provided postural support but did not influence the visual experience. Results showed that the addition of the postural support improved performance. These findings suggest that neuromuscular, and perhaps biomechanical, constraints contribute more to the influence of spatial orientation than visual-perceptual constraints.

Adult↗
PubMed2006

Visual spatial clues enhance ocular torsion response during visual tilt.

Ocular torsion in response to a static tilt of a visual stimulus has been, and still remains in doubt. Furthermore, the possible underlying mechanism is not well understood. The authors' hypothesize that if the torsional response is related to the vestibular otolith system, then a visual stimulus with spatial clues important for maintaining body posture will induce a larger torsional response as compared to a stimulus lacking spatial information. Eye movements were recorded objectively in 15 healthy individuals using a 3D video oculography system. Three visual stimuli were used. In two tests, an identical photographic image of a city scene with spatial clues relevant for body posture were used, with the only difference being a square periphery in one stimulus (test 1) and a circular periphery in the other (test 2). The third stimulus (test 3) consisted of yellow rectangles on a black background with no natural spatial information. The scenes were tilted in 15 degrees steps from 0 degrees to 45 degrees in CCW and CW direction, and each position were held static for 15 s. All visual scene tilts induced a compensatory torsional response, which increased with stimuli angle. The stimuli with spatial clues induced more torsion compared to the stimulus without spatial clues. No difference was found when analysing the peripheral contour effect or direction of stimulus tilt. The present results support the hypothesis of an origin in the otolith system for the torsional response found to a static tilted visual scene.

Adolescent↗
PubMed1998

Spatial disparity affects visual-auditory interactions in human sensorimotor processing.

Information from the auditory and visual systems converges in the nervous system with physiological and behavioral consequences. Most of our knowledge about the rules governing such convergence has been obtained in experiments where the strength or the timing of the individual auditory and visual stimuli has been varied. Relatively little attention has been paid to the spatial relationship between different modalities of stimuli in multisensory experiments. We studied saccadic reaction times of human subjects to bimodal auditory and visual stimulus presentations under two conditions: first, with the targets spatially coincident and, second, with various degrees of spatial separation or disparity. In the first experiment, we found that the saccadic reaction times were consistently shorter than would be predicted by independent processing of information about the visual and auditory targets. These results suggest convergence of multimodal information at one or more loci within the nervous system. In the second experiment, we found that saccadic latency gradually increased as spatial distance between the auditory and visual targets increased. Evidence for neural summation was found over a wide range of spatial disparities. These results suggest that multisensory information can be integrated and have significant influences on behavior over a surprisingly large range of spatial disparity.

Eye Movements↗
PubMed2006

The influence of photon depth of interaction and non-collinear spread of annihilation photons on PET image spatial resolution.

PURPOSE: The quality of PET imaging is impaired by parallax errors. These errors produce misalignment between the projected location of the true origin of the annihilation event and the line of response determined by the coincidence detection system. Parallax errors are due to the varying depths of photon interaction (DOI) within the scintillator and the non-collinear (NC) emission of the annihilation photons. The aim of this work was to address the problems associated with the DOI and the NC spread of annihilation photons and to develop a quantitative model to assess their impact on image spatial resolution losses for various commonly used scintillators and PET geometries. METHODS: A theoretical model based on Monte Carlo simulations was developed to assess the relative influence of DOI and the NC spread of annihilation photons on PET spatial resolution for various scintillator materials (BGO, LSO, LuAP, GSO, NaI) and PET geometries. RESULTS: The results demonstrate good agreement between simulated, experimental and published overall spatial resolution for some commercial systems, with maximum differences around 1 mm in both 2D and 3D mode. The DOI introduces an impairment of non-stationary spatial resolution along the radial direction, which can be very severe at peripheral positions. As an example, the radial spatial resolution loss due to DOI increased from 1.3 mm at the centre to 6.7 mm at 20 cm from the centre of a BGO camera with a 412-mm radius in 2D mode. Including the NC, the corresponding losses were 3.0 mm at the centre and 7.3 mm 20 cm from the centre. CONCLUSION: Without a DOI detection technique, it seems difficult to improve PET spatial resolution and increase sensitivity by reducing the detector ring radius or by extending the detector in the axial direction. Much effort is expended on the design and configuration of smaller detector elements but more effort should be devoted to the DOI complexity.

Artifacts↗
PubMed2006

Competing populations on fragmented landscapes with spatially structured heterogeneities: improved landscape generation and mixed dispersal strategies.

Interactions between two species competing for space were studied using stochastic spatially explicit lattice-based simulations as well as pair approximations. The two species differed only in their dispersal strategies, which were characterized by the proportion of reproductive effort allocated to long-distance (far) dispersal versus short-distance (near) dispersal to adjacent sites. All population dynamics took place on landscapes with spatially clustered distributions of suitable habitat, described by two parameters specifying the amount and the local spatial autocorrelation of suitable habitat. Whereas previous results indicated that coexistence between pure near and far dispersers was very rare, taking place over only a very small region of the landscape parameter space, when mixed strategies are allowed, multiple strategies can coexist over a much wider variety of landscapes. On such spatially structured landscapes, the populations can partition the habitat according to local conditions, with one species using pure near dispersal to exploit large contiguous patches of suitable habitat, and another species using mixed dispersal to colonize isolated smaller patches (via far dispersal) and then rapidly exploit those patches (via near dispersal). An improved mean-field approximation which incorporates the spatially clustered habitat distribution is developed for modeling a single species on these landscapes, along with an improved Monte Carlo algorithm for generating spatially clustered habitat distributions.

Computer Simulation↗
PubMed2002

Spatial domain image filtering in computed tomography: feasibility study in pulmonary embolism.

Our objective was to evaluate the clinical feasibility of spatial domain filtering as an alternative to additional image reconstruction using different kernels in chest CT. Spatial domain filtering generates smooth images from sharp images and thus avoids the need for additional reconstructions when two sets of images are desired. Forty adult patients with clinical suspicion of pulmonary embolism were examined utilizing multi-slice CT (Somatom Volume Zoom, Siemens, Germany). Derived from thin collimated source images (100 mAs, collimation 4x1 mm, rotation time 0.5 s, table speed 7 mm/rotation), two sets of images [effective slice thickness (S(eff)) 5 mm, reconstruction increment (RI) 5 mm) were generated using lung (Siemens B50) and soft tissue (Siemens B30) kernels. Additionally, B50 images were filtered in the spatial domain, producing images largely equivalent to B30 images. Firstly, diagnostic accuracy was assessed on spatial domain filtered images regarding central, segmental, and subsegmental pulmonary embolism. In a second step, diagnostic accuracy was assessed for the initially reconstructed B30 images. The results were compared with thin axial slices from the same data set, which were considered as the gold standard in this respect (S(eff )1.25 mm, RI 0.8 mm; B30). Initially reconstructed B30 slices and secondary filtered images were rated for subjective image quality, using a five-point scale (1=excellent, 2=good, 3=moderate, 4=poor, 5=non-diagnostic). Finally, quantitative measurements were assessed using the region of interest (ROI) methodology. In 20 patients pulmonary embolism was proven. Five-millimeter images revealed 10 of 10 central emboli, 18 of 19 segmental thrombi, and 18 of 20 emboli on the subsegmental level. Pulmonary embolism was excluded in 18 of 20 subjects, and in 2 patients a false-positive result was obtained in subsegmental arteries. These findings were concordant for reconstructed and filtered images. Quantitative density measurements provided comparable Hounsfield units in this respect. Subjective gradings of image quality, based on soft tissue settings, were 1.30 (+/-0.61) for reconstructed slices vs 1.35 (+/-0.62) for filtered images (weighted kappa coefficient 0.6117; 95% confidence intervals 0.3298-0.8935). Spatial domain filtering has proved to be feasible. Compared with conventional soft tissue reconstructions for central, segmental, and subsegmental pulmonary embolism, no significant difference in the diagnostic value of spatial domain filtered images was found. Online modifications of image sharpness and pixel noise in real time leads to a considerable reduction of processing time and cost saving for storage of CT images. Despite different data processing methods, thin effective slice thicknesses and overlapping reconstruction increments are mandatory for detailed CT analysis of pulmonary embolism on the segmental and subsegmental level.

Feasibility Studies↗
PubMed2005

MRI of the pelvis at 3 T: very high spatial resolution with sensitivity encoding and flip-angle sweep technique in clinically acceptable scan time.

OBJECTIVE: The higher signal at 3.0-T allows spatial resolution to be increased without loss in image quality. We evaluated a T2-weighted turbo spin-echo sequence with high spatial resolution (3T-HR) to determine whether this provides clinically useful pelvic MRI. MATERIALS AND METHODS: We designed a sequence with high spatial resolution (3T-HR) (0.45x0.46x4 mm) that was combined with parallel imaging and the variable refocusing angle technique (8.06 min). We examined 23 patients with gynecological disorders using 3T-HR and a standard sequence (3T-SP; 4.03 min; equivalent to 1.5 T). Two radiologists analyzed tissue contrast, signal to noise, detail delineation and artifact level. RESULTS: Tissue contrasts and signal to noise were rated equal. Motion artifacts occurred more often with 3T-SP despite the longer scanning time of 3T-HR. The higher spatial resolution provided additional information in four patients. In two patients small myomas were detected, in one patient a lymph node metastasis was apparent, and in one patient 3T-HR excluded tumor invasion. CONCLUSIONS: High spatial resolution pelvic studies with high image quality can be obtained at 3 T in acceptable scan time. The higher spatial resolution that is feasible at 3 T also provides more clinically relevant information.

Adolescent↗
PubMed2004

Deficits of spatial localization in children with strabismic amblyopia.

BACKGROUND: Besides loss of visual acuity and binocularity, spatial localization deficits (comprising both increased spatial uncertainty and spatial distortions) are an important feature of strabismic amblyopia. Although they have been extensively investigated in adult amblyopes, there are still many open questions concerning their substrate and relationship to clinical parameters. Our aim was to develop a procedure for assessing vertical alignment, which enabled us to find out whether children with strabismic amblyopia had similar spatial localization deficits, and their relation to the children's clinical condition. METHODS: Vertical alignment was assessed in children by comparing the visual direction in space of three loci along the vertical meridian, separated by 5 deg of visual angle. We tested alignment in the amblyopic and dominant eyes of 32 strabismic and in both eyes of 35 control children from 4.5 to 10 years, together with a careful orthoptic examination. RESULTS: In the amblyopic eyes, increased uncertainty and systematic distortions outside the normal range occurred. Large angles of deviation and pathological fixation patterns were necessary, but not sufficient conditions for gross spatial deficits to occur. The fellow dominant eyes showed spatial localization similar to normal eyes. CONCLUSIONS: Children with strabismic amblyopia exhibited localization deficits and relationship to clinical data similar to those in adult amblyopes. These data are important for further investigations about the substrate, plasticity and the clinical relevance of perceptual distortions.

Amblyopia↗
PubMed2000

Conditions for noise reduction and stable encoding of spatial structure by cortical neural networks.

Cortical circuits have been proposed to encode information by forming stable spatially structured attractors. Experimentally in the primary somatosensory cortex of the monkey, temporally invariant stimuli lead to spatially structured activity patterns. The purpose of this work is to study a recurrent cortical neural network model with lateral inhibition and examine what effect additive random noise has on the networks' ability to form stable spatially structured representations of the stimulus pattern. We show numerically that this network performs edge enhancement and forms statistically stationary, spatially structured responses when the lateral inhibition is of moderate strength. We then derive analytical conditions on the connectivity matrix that ensure stochasticly stable encoding of the stimulus spatial structure by the network. For stimuli whose strength falls in the near linear region of the sigmoid, we are able to give explicit conditions on the eigenvalues of the connection matrix. Finally, we prove that a network with a connection matrix, where the total excitation and inhibition impinging upon a neural unit are nearly balanced, will yield stable spatial attractor responses.

Animals↗
PubMed2004

Right-left prevalence with task-irrelevant spatial codes.

The present work investigated the right-left prevalence effect caused by the automatic activation of horizontal and vertical spatial codes in a task (Simon task) in which spatial information is task-irrelevant. Experiment 1 showed a horizontal Simon effect and a vertical Simon effect with a two-dimensional stimulus-response set. In Experiments 2 and 3, the right-left prevalence was obtained in two-dimensional Simon tasks with two contralateral effectors and four effectors respectively. Experiment 4 showed that horizontal coding is based on multiple spatial codes, whereas only one spatial code was formed for vertical coding. On the whole, these results support the notion that the right-left prevalence effect is a general phenomenon affecting spatial coding, and suggest that the horizontal dimension is prevalent because it is based on multiple spatial codes.

Analysis of Variance↗
PubMed2006

Working memory components and imagery instructions in the elaboration of a spatial mental model.

The paper investigates the involvement of verbal and visuo-spatial working memory during the processing of spatial texts via a dual-task paradigm. Subjects were presented with three texts describing locations from a route perspective, and had either to imagine themselves moving along a route in surroundings or to rehearse verbal information. Concurrently they had to perform a spatial tapping task, an articulatory task, or no secondary task. Performance on a verification test used to assess the product of comprehension showed that the concurrent tapping task impaired performance in the imagery instructions group but not in the repetition instructions group, and caused the beneficial effect of imagery instructions to vanish. This result was not observed with the articulatory task, where interference effects were similar in both instructions groups. Performance on the concurrent tasks confirmed the pattern obtained with the verification test. In addition, results seem partly dependent on the capacity of spatial working memory as measured by the Corsi Blocks Test. We argue that these results clarify the processes of the construction of a spatial mental model, and confirm that the visuo-spatial working memory is involved in mental imagery.

Adult↗
PubMed2003

Spatial variation in springtime food resources influences the winter body mass of roe deer fawns.

It is well established that the dynamics of mammalian populations vary in time, in relation to density and weather, and often in interaction with phenotypic differences (sex, age and social status). Habitat quality has recently been identified as another significant source of individual variability in vital rates of deer, including roe deer where spatial variations in fawn body mass were found to be only about a tenth of temporal variations. The approach used was to classify the habitat into blocks a priori, and to analyse variation in animal performance among the predefined areas. In a fine-grained approach, here we use data collected over 24 years on 1,235 roe deer fawns captured at known locations and the plant species composition sampled in 2001 at 578 sites in the Chizé forest to determine the spatial structure at a fine scale of both vegetation and winter body mass of fawns, and then to determine links between the two. Space and time played a nearly equal role in determining fawn body masses of both sexes, each accounting for about 20% of variance and without any interaction between them. The spatial distribution of fawn body mass was perennial over the 24 years considered and predicted values showed a 2 kg range according to location in the reserve, which is much greater than suggested in previous work and is enough to have strong effects on fawn survival. The spatial distribution and the range of predicted body masses were closely similar in males and females. The result of this study is therefore consistent with the view that the life history traits of roe deer are only weakly influenced by sexual selection. The occurrence of three plant species that are known to be important food items in spring/summer roe deer diets, hornbeam ( Carpinus betulus), bluebell ( Hyacinthoides sp.) and Star of Bethlehem ( Ornithogalum sp.) was positively related to winter fawn body mass. The occurrence of species known to be avoided in spring/summer roe deer diets [e.g. butcher's broom ( Ruscus aculeatus) and beech ( Fagus sylvatica)], was negatively related to fawn body mass. We conclude that the spatial variation in the body mass of fawns in winter in this forest is as important as the temporal variation, and that the distribution of plant species that are actively selected during spring and summer is an important determinant of spatial variation in winter fawn body mass. The availability of these plants is therefore likely to be a key factor in the dynamics of roe deer populations.

Adaptation, Physiological↗
PubMed2004

How do frugivores track resources? Insights from spatial analyses of bird foraging in a tropical forest.

Frugivores often track ripe fruit abundance closely across local areas despite the ephemeral and typically patchy distributions of this resource. We use spatial auto- and cross-correlation analyses to quantify spatial patterns of fruit abundance and avian frugivory across a 4-month period within a forested 4.05-ha study grid in Puerto Rico. Analyses focused on two tanager species, Spindalis portoricensis and Nesospingus speculiferus, and their principal food plants. Three broad questions are addressed: (1). at what spatial scales is fruit abundance and frugivory patchy; (2). at what spatial scales do frugivores respond to fruit abundance; and (3). to what extent do spatial patterns of frugivory overlap between bird species? Fruit patch size, species composition, and heterogeneity was variable among months, despite fruit patch locations remaining relatively consistent between months. Positive correlations between frugivory and fruit abundance suggested tanagers successfully tracked fruit abundance. Frugivory was, however, more localized than fruit abundance. Scales of spatial overlap in frugivory and monthly variation in the foraging locations of the two tanager species suggested that interspecific facilitation may have been important in determining bird foraging locations. In particular, S. portoricensis, a specialist frugivore, may have relied on the loud calls of the gregarious generalist, N. speculiferus, to find new foraging areas. Such a mechanism could help explain the formation of mixed species feeding flocks and highlights the potential importance of facilitation between species that share resources.

Animals↗
PubMed2006

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community.

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 x 2 m plot, we assessed AMF inoculum potential at a depth of 0-6 and 6-12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6-12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2-14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales.

DNA, Fungal↗
PubMed2006

Patterns of spatial autocorrelation in stream water chemistry.

Geostatistical models are typically based on symmetric straight-line distance, which fails to represent the spatial configuration, connectivity, directionality, and relative position of sites in a stream network. Freshwater ecologists have explored spatial patterns in stream networks using hydrologic distance measures and new geostatistical methodologies have recently been developed that enable directional hydrologic distance measures to be considered. The purpose of this study was to quantify patterns of spatial correlation in stream water chemistry using three distance measures: straight-line distance, symmetric hydrologic distance, and weighted asymmetric hydrologic distance. We used a dataset collected in Maryland, USA to develop both general linear models and geostatistical models (based on the three distance measures) for acid neutralizing capacity, conductivity, pH, nitrate, sulfate, temperature, dissolved oxygen, and dissolved organic carbon. The spatial AICC methodology allowed us to fit the autocorrelation and covariate parameters simultaneously and to select the model with the most support in the data. We used the universal kriging algorithm to generate geostatistical model predictions. We found that spatial correlation exists in stream chemistry data at a relatively coarse scale and that geostatistical models consistently improved the accuracy of model predictions. More than one distance measure performed well for most chemical response variables, but straight-line distance appears to be the most suitable distance measure for regional geostatistical modeling. It may be necessary to develop new survey designs that more fully capture spatial correlation at a variety of scales to improve the use of weighted asymmetric hydrologic distance measures in regional geostatistical models.

Databases, Factual↗