Influence of adaptation to horizontal body position on pointing errors and visual estimation of a target position in humans

The central program of a targeted movement includes a component intended for to compensate for the weight of the arm; this is why the accuracy of pointing to a memorized position of the visual target in darkness depends on orientation of the moving limb in relation to the vertical axis. Transition from the vertical to the horizontal body position is accompanied by a shift of the final hand position along the body axis towards the head. We studied how pointing errors and visual localization of the target are modified due to adaptation to the horizontal body position; targeted movements to a real target were repeatedly performed during the adaptation period. Three types of experiments were performed: a basic experiment, and two different experiments with adaptation realized under somewhat dissimilar conditions. In the course of the first adaptation experiment, subjects received no visual information on the hand’s position in space, and targeted movements of the arm to a luminous target could be corrected using proprioceptive information only. With such a paradigm, the accuracy of pointing to memorized visual targets showed no adaptation-related changes. In the second adaptation experiment, subjects were allowed to continuously view a marker (a light-emitting diode taped to the fingertip). After such adaptation practice, the accuracy of pointing movements to memorized targets increased: both constant and variational errors, as well as both components of constant error (i.e.,X andY errors) significantly dropped. Testing the accuracy of visual localization of the targets by visual/verbal adjustment, performed after this adaptation experiment, showed that the pattern of errors did not change compared with that in the basic experiment. Therefore, we can conclude that sensorimotor adaptation to the horizontal position develops much more successfully when the subject obtains visual information about the working point position; such adaptation is not related to modifications in the system of visual localization of the target.     

Variation in natural head position and establishing corrected head position

Corrected head position (CHP) has been simulated by using the Frankfurt horizontal (FH) for over 100 years but FH varies between individuals. Because CHP is biologically relevant for orthodontic diagnosis and treatment planning, orthognathic surgical planning, and art, this study examined relationships between head position and selected cephalometric planes.     

The role of perceived relative position in pointing to objects apparently shifted by depth-contrast

This paper is concerned with the information used in open-loop pointing to visually perceived targets. Stereoscopic stimuli were used to produce illusory relative egocentric distances, which were inconsistent with the angles of vergence required to fuse the targets. One of the stimuli was a rectangle slanted around a vertical axis. Four participants in Experiment 1 reported its slant and pointed to its edges. The slant was hugely underestimated (condition A) unless the rectangle was flanked by other surfaces (condition B). The relative depth of a pair of dots placed in front of the rectangle was also misperceived due to depth-contrast effect. The critical finding is that pointing responses were not based on vergence but were consistent with depth estimates, both for the rectangle and for the dots. Experiment 2 revealed the conditions necessary for pointing to be consistent with perceived relative position. The different target distances were either randomised allowing inter-trial comparisons, or presented only one per session to prevent them. Pointing was similar to estimates only in the randomised condition showing the significance of inter-trial comparisons. It is proposed that participants used the remembered motor command and kinesthetic sensations of a previous movement as a reference, attempting to make the difference between successive movements the same as a visually perceived depth difference between successive targets.     

Variations with position of replication errors due to exonuclease warm-up

A.A mismatch errors occurring during poly(dA) replication with the Klenow fragment of E. coli DNA polymerase I have been quantified. The A/T ratio measured for chains extended by 1-25 nucleotides decreases by a factor of at least 15 from beginning to end. The deduced true error rate may decrease by a factor of 2.5 at each successive nucleotide addition. When ddATP is used instead of dATP, the ddA/T ratio indicates little variation of the misincorporation probability with position. Thus, the accuracy improvement in the first case is due to a warm-up of the proofreading function.     

A new calibration method for 3-D position measurement in biomedical applications.

Aim of the study was to determine practicality and to test accuracy of a new calibration technique firstly introduced in 1998 by Schmid and Bess for biomechanical human tests. This technique enables three-dimensional calibration of camera positions as well as the calculation of internal and external camera parameters. It can be performed unlike other three-dimensional calibration techniques as the first with a planar calibration grid and only one single video image (of each camera) to calculate all 3-D reconstruction parameters. The tests were performed using two albavision ACAM G-Cameras with a resolution of 480 (h) by 420 (v) pixels. The achievable accuracy of distance measurements in recent commercially available motion measurement systems usually ranges from about 0.09% to 1.77% and higher. Accuracy of 0.0373% was determined with the new calibration technique. The 95% confidence interval ranged at +/- 0.02322 mm, the RMS (root mean square) error at 0.18776 mm. Better accuracy, easier and faster calibration are features of this new calibration technique. Required time for complete calibration ranged below one minute. Anticipating this new method will have good practicality in gait analysis or in research and industry due to increased accuracy and ease of use.     

Estimating alignment errors in sets of 2-D images

We describe a robust and accurate method for the estimation of alignment errors for a set of two-dimensional images, in the case where the true pattern is unknown. The intended application of the proposed method is cryo-electron microscopy, where two-dimensional views of individual proteins in random orientations are observed in the electron microscope at low signal-to-noise ratio. By representing images in the basis of Fourier-harmonic coordinates and constructing averages and average intensities, we demonstrate that the variances of translation and rotational errors as well as of the Gaussian noise can be recovered. This machinery therefore allows one to isolate the various categories of errors that impede the quality of results in single particle reconstructions into constituent parts: translational errors, rotational errors, and additive noise.     

Finite-element simulation of cooling of realistic 3-D human head and neck

Rapid cooling of the brain in the first minutes following the onset of cerebral ischemia is a potentially attractive preservation method. This computer modeling study was undertaken to examine brain-cooling profiles in response to various external cooling methods and protocols, in order to guide the development of cooling devices suitable for deployment on emergency medical vehicles. The criterion of successful cooling is taken to be the attainment of a 33 degrees C average brain temperature within 30 min of treatment. The transient cooling of an anatomically correct realistic 3-D head and neck with realistically varying local tissue properties was numerically simulated using the finite-element method (FEM). The simulations performed in this study consider ice packs applied to head and neck as well as using a head-cooling helmet. However, it was found that neither of these cooling approaches satisfies the 33 degrees C temperature within 30 min. This central conclusion of insubstantial cooling is supported by the modest enhancements reported in experimental investigations of externally applied cooling. The key problem is overcoming the protective effect of warm blood perfusion, which reaches the brain via the uncooled carotid arterial supply and effectively blocks the external cooling wave from advancing to the core of the brain. The results show that substantial cooling could be achieved in conjunction with neck cooling if the blood speed in the carotid artery is reduced from normal by a factor of 10. The results suggest that additional cooling means should be explored, such as cooling of other pertinent parts of the human anatomy.     

Influence of head position on carotid hemodynamics in young adults

Studies in adults have shown marked changes in geometry and relative positions of the carotid arteries when rotating the head. The aim of this study was to quantify the change in geometry and analyze its effect on carotid hemodynamics as a result of head rotation. The right carotid arteries of nine young adult subjects were investigated in supine position with straight and left turned head positions, respectively. The three-dimensional (3D) carotid geometry was reconstructed by using 3D ultrasound (3D US), and the carotid hemodynamics were calculated by combining 3D US with computational fluid dynamics. It was observed that cross-sectional areas and shapes did not change markedly with head rotation, but carotid vessel center lines altered with planarification of the common carotid artery as a main feature (P < 0.05). Measured common carotid flow rates changed significantly at the individual level when the head was turned, but on the average, the change in mean common carotid flow rate was relatively small (0.37 +/- 1.11 ml/s). The effect of the altered center lines and flow rates on the atherogenic nature of the carotid bifurcation was evaluated by using calculated hemodynamic wall parameters, such as wall shear stress (WSS) and oscillatory shear index (OSI). It was found that WSS and OSI patterns changed significantly with head rotation, but the variations were very subject dependent and could not have been predicted without assessing the altered geometry and flow of the carotid bifurcation for individual cases. This study suggests that there is a need for standardization of the choice of head position in the 3D US scan protocol, and that carotid stents and emboli diverters should be studied in different head positions.     

Effects of pore size in 3-D fibrous matrix on human trophoblast tissue development

The effects of pore size in a 3-D polyethylene terephthalate (PET) nonwoven fibrous matrix on long-term tissue development of human trophoblast ED27 cells were studied. Thermal compression was used to modify the porosity and pore size of the PET matrix. The pore size distributions in PET matrices were quantified using a liquid extrusion method. Cell metabolic activities, estradiol production, and cell proliferation and differentiation were studied for ED27 cells cultured in the thermally compressed PET matrices with known pore structure characteristics. In general, metabolic activities and proliferation rate were higher initially for cultures grown in the low-porosity (LP) PET matrix (porosity of 0.849, average pore size of 30 microm in diameter) than those in the high-porosity (HP) matrix (porosity of 0.896, average pore size of 39 microm in diameter). However, 17beta-estradiol production and cell differentiation activity in the HP matrix surpassed those in the LP matrix after 12 days. The expression levels of cyclin B1 and p27kip1 in cells revealed progressively decreasing proliferation and increasing differentiation activities for cells grown in PET matrices. Also, difference in pore size controlled the cell spatial organization in the PET matrices and contributed to the tissue development in varying degrees of proliferation and differentiation. It was also found that cells grown on the 2-D surface behaved differently in cell cycle progression and did not show increased differentiation activities after growth had stopped and proliferation activities had lowered to a minimal level. The results from this study suggest that the 3-D cell organization guided by the tissue scaffold is important to tissue formation in vitro.     

Effects of computing parameters and measurement locations on the estimation of 3D NPS in non-stationary MDCT images

The goal of this study was to investigate the impact of computing parameters and the location of volumes of interest (VOI) on the calculation of 3D noise power spectrum (NPS) in order to determine an optimal set of computing parameters and propose a robust method for evaluating the noise properties of imaging systems.Noise stationarity in noise volumes acquired with a water phantom on a 128-MDCT and a 320-MDCT scanner were analyzed in the spatial domain in order to define locally stationary VOIs. The influence of the computing parameters in the 3D NPS measurement: the sampling distances b_x,y,z and the VOI lengths L_x,y,z, the number of VOIs N_VOI and the structured noise were investigated to minimize measurement errors. The effect of the VOI locations on the NPS was also investigated.Results showed that the noise (standard deviation) varies more in the r-direction (phantom radius) than z-direction plane. A 25 × 25 × 40 mm³ VOI associated with DFOV = 200 mm (L_x,y,z = 64, b_x,y = 0.391 mm with 512 × 512 matrix) and a first-order detrending method to reduce structured noise led to an accurate NPS estimation. NPS estimated from off centered small VOIs had a directional dependency contrary to NPS obtained from large VOIs located in the center of the volume or from small VOIs located on a concentric circle. This showed that the VOI size and location play a major role in the determination of NPS when images are not stationary.This study emphasizes the need for consistent measurement methods to assess and compare image quality in CT.     

Effects of Texture Component Orientation on Orientation Flow Visibility for 3-D Shape Perception

In images of textured 3-D surfaces, orientation flows created by the texture components parallel to the surface slant play a critical role in conveying the surface slant and shape. This study examines the visibility of these orientation flows in complex patterns. Specifically, we examine the effect of orientation of neighboring texture components on orientation flow visibility. Complex plaids consisting of gratings equally spaced in orientation were mapped onto planar and curved surfaces. The visibility of the component that creates the orientation flows was quantified by measuring its contrast threshold (CT) while varying the combination of neighboring components present in the pattern. CTs were consistently lowest only when components closest in orientation to that of the orientation flows were subtracted from the pattern. This finding suggests that a previously reported frequency-selective cross-orientation suppression mechanism involved with the perception of 3-D shape from texture is affected by proximity in orientation of concurrent texture components.     

Kinesin Kar3 and Vik1 go head to head

The yeast kinesin motor protein Kar3 forms a heterodimer with a nonmotor protein Vik1. A study in this issue by Allingham et al. (2007) reveals that Vik1 unexpectedly has a structure similar to a kinesin motor domain yet lacks a nucleotide-binding site and is thus catalytically inactive. However, this does not hinder movement of the heterodimer because other features of the remarkably divergent Vik1 motor domain are retained, including the ability to bind microtubules.     

Effects of genotyping errors on parentage exclusion analysis

Genetic markers are widely used to determine the parentage of individuals in studies of mating systems, reproductive success, dispersals, quantitative genetic parameters and in the management of conservation populations. These markers are, however, imperfect for parentage analyses because of the presence of genotyping errors and undetectable alleles, which may cause incompatible genotypes (mismatches) between parents and offspring and thus result in false exclusions of true parentage. Highly polymorphic markers widely used in parentage analyses, such as microsatellites, are especially prone to genotyping errors. In this investigation, I derived the probabilities of excluding a random (related) individual from parentage and the probabilities of Mendelian-inconsistent errors (mismatches) and Mendelian-consistent errors (which do not cause mismatches) in parent-offspring dyads, when a marker having null alleles, allelic dropouts and false alleles is used in a parentage analysis. These probabilities are useful in evaluating the impact of various types of genotyping errors on the information content of a set of markers in and thus the power of a parentage analysis, in determining the threshold number of genetic mismatches that is appropriate for a parentage exclusion analysis and in estimating the rates of genotyping errors and frequencies of null alleles from observed mismatches between known parent-offspring dyads. These applications are demonstrated by numerical examples using both hypothetical and empirical data sets and discussed in the context of practical parentage exclusion analyses.     

Molecular phylogeny in 3-D

Molecular phylogenetic trees are constructed in three dimensions relative to the distribution of MW and pl classes and immunocrossreactivity against polyclonal antibodies to lens crystallins, as well as multiple sequence alignment between amino acid sequences, coding nucleotide sequences and the gene nucleotide sequences for beta-globin. Euclidian distances are estimated to position species in x, y, z space by multidimensional scaling and merged with bootstrap-tested branching pattern of Fitch & Margoliash plots to obtain 3-D phylogenetic tree. Compared to single attributes, phylogenetic trees based on multiple parameters allow significant repositioning of rodents, chiroptera and primates.     

Development of an optical 3-D position measuring system for simultaneous detection of 6 degrees of freedom]

A few years ago it became possible to carry out complicated surgical procedures in humans with the required precision by combining medical imaging (MRI, CT) with minimally invasive surgery. The confined space within these imaging systems and the resulting inaccuracies associated with the manual use of instruments increasingly make necessary the help of aids ranging from positioning systems to robotic devices, which themselves must be position controlled. A position sensor has been developed for a medical robotic system allowing the image-controlled insertion of injection needles and the simultaneous administration of different drugs. The 3D position coordinates are determined by a noncontact optical principle, which also enables simultaneous determination of all 6 basic degrees of freedom of the robotic system (3 translational, 3 rotational). On the basis of an area image sensor and the measurement of a geometrically defined structure in the path of the rays between sensor and light source, the position coordinates are calculated almost real time. Special emphasis was placed on designing the sensor system to cover a sufficiently large workspace to enable it to cover the entire intervention area. The sensor described herein determines the position coordinates in a volume of 10 x 10 x 10 cm at a resolution of up to 1 mm for translations and 1 degree for rotations.     

Effects of remedies made in patient setup process on residual setup errors and margins in head and neck cancer radiotherapy based on 2D image guidance

AimPatient setup errors were aimed to be reduced in radiotherapy (RT) of head-and-neck (H&N) cancer. Some remedies in patient setup procedure were proposed for this purpose.BackgroundRT of H&N cancer has challenges due to patient rotation and flexible anatomy. Residual position errors occurring in treatment situation and required setup margins were estimated for relevant bony landmarks after the remedies made in setup process and compared with previous results.Materials and methodsThe formation process for thermoplastic masks was improved. Also image matching was harmonized to the vertebrae in the middle of the target and a 5 mm threshold was introduced for immediate correction of systematic errors of the landmarks. After the remedies, residual position errors of bony landmarks were retrospectively determined from 748 orthogonal X-ray images of 40 H&N cancer patients. The landmarks were the vertebrae C1–2, C5–7, the occiput bone and the mandible. The errors include contributions from patient rotation, flexible anatomy and inter-observer variation in image matching. Setup margins (3D) were calculated with the Van Herk formula.ResultsSystematic residual errors of the landmarks were reduced maximally by 49.8% (p ≤ 0.05) and the margins by 3.1 mm after the remedies. With daily image guidance the setup margins of the landmarks were within 4.4 mm, but larger margins of 6.4 mm were required for the mandible.ConclusionsRemarkable decrease in the residual errors of the bony landmarks and setup margins were achieved through the remedies made in the setup process. The importance of quality assurance of the setup process was demonstrated.     

Effects of random and non-random errors on phenotypic selection in autotetraploids

Summary A theoretical investigation was made to ascertain the effects of random and non-random deviations, called errors, of phenotypic from genotypic values on population means and on the response to phenotypic recurrent selection. The study was motivated as a selection experiment for disease resistance where there was either variability in the inoculation or environment (the random errors) or where the inoculation was above or below the the optimum rate where genetic differences in resistance are maximized (the non-random errors). The study was limited to the genetics at a diallelic locus (alleles B and b) in an autotetraploid population in random mating equilibrium. The response to selection was measured as the covariance of selection and compared to the exact covariance which was the covariance of selection without errors in phenotype. The random errors were modeled by assuming that a given percentage () of the population was uniformly distributed among the five possible genotype classes independent of their true genotypes. This model was analyzed numerically for a theoretical population with the frequency of the B allele (p) ranging from 0.0 to 1.0 and assumed errors of=0.1 and 0.5 for the following six types of genic action of the B allele: additive, monoplex dominance, partial monoplex dominance, duplex dominance, partial duplex dominance, and recessive. The effect of random error was to consistently reduce the response to selection by a percentage independent of the type of genic action at the locus. The effect on the population mean was an upward bias when p was low and a downward bias when p approached unity. In the non-random error model below optimum inoculations altered the phenotypes by systematically including percentage of susceptible genotypes into one or more other genotype classes with more genetic resistance (a positive shift). With above optimum inoculations, some resistant genotypes are classed with the non-resistant genotypes (a negative shift). The effects on the covariance of selection were found by numerical analysis for the same types of genic action and's as investigated for random error. With a negative shift and a low p, the covariance of selection was always reduced, but for an increasing p the covariance approached and exceeded the exact covariance for all types of genic action except additive. With a positive shift and a low p, response to selection was greatly improved for three types of genic action: duplex dominance, partial duplex dominance, and recessive. The effect of a non-random error on population means was to greatly bias the means upwards for a low p and positive shift, but with increasing p the bias decreased. A relatively slight decrease in the mean occurred with a negative shift. This study indicated check varieties commonly used to monitor selection pressures in screening programs are very responsive to positive non-random shifts, but are relatively unresponsive to negative shifts. The interaction of selection pressure, types of genic action, and genotypes in the class shift models was suggested as a partial explanation for the lack of response to increasing selection pressures observed in some breeding programs.Cooperative investigations of the Alfalfa Production Research Unit, United States Department of Agriculture, Agricultural Research Service, and the Nevada Agricultural Experiment Station, Reno, Nevada. Paper No. 404 Scientific Journal Series. Nevada Agricultural Experiment Station     

Deconvolution in 3-D optical microscopy

Summary Fluorescent probes are becoming ever more widely used in the study of subcellular structure, and determination of their three-dimensional distributions has become very important. Confocal microscopy is now a common technique for overcoming the problem of out-of-focus flare in fluorescence imaging, but an alternative method uses digital image processing of conventional fluorescence images — a technique often termed deconvolution or restoration. This review attempts to explain image deconvolution in a non-technical manner. It is also applicable to 3-D confocal images, and can provide a further significant improvement in clarity and interpretability of such images. Some examples of the application of image deconvolution to both conventional and confocal fluorescence images are shown.     

Mechanical testing of cancellous bone from the femoral head: experimental errors due to off-axis measurements

The aim of this study was to verify whether a misalignment between the testing direction and the trabecular main direction has a significant effect on the compressive behaviour of cancellous bone. Ten cylindrical specimens were extracted from femoral heads with a misalignment to the trabecular main direction of approximately 20 degrees. Each specimen was paired with a specimen extracted aligned with the main direction of the trabeculae on the basis of the closest bone volume fraction, obtaining two groups, one 'aligned' and one 'misaligned'. The average off-axis angle was 6.1 degrees and 21.6 degrees for the 'aligned' and 'misaligned' group, respectively. The specimens underwent micro-tomographic analysis, compressive testing, micro-indentation testing and ashing. No significant differences were found in histomorphometric parameters, hardness and ash density between the two groups, whereas significant differences were found in Young's modulus and ultimate stress: both parameters, measured for the 'misaligned' group, were about 40% lower than those measured for the 'aligned' group. These results demonstrate a great effect of the angle between the testing direction and the main direction of the trabecular structure on the compressive behaviour of cancellous bone. This angle should be reduced as much as possible (in the present work the average value was 6.6+/-3.3 degrees), in any case measured, and always reported together with the mechanical parameters of cancellous bone.