Heading judgments during active and passive self-motion

Previous studies have generally considered heading perception to be a visual task. However, since judgments of heading direction are required only during self-motion, there are several other relevant senses which could provide supplementary and, in some cases, necessary information to make accurate and precise judgments of the direction of self-motion. We assessed the contributions of several of these senses using tasks chosen to reflect the reference system used by each sensory modality. Head-pointing and rod-pointing tasks were performed in which subjects aligned either the head or an unseen pointer with the direction of motion during whole body linear motion. Passive visual and vestibular stimulation was generated by accelerating subjects at sub- or supravestibular thresholds down a linear track. The motor-kinesthetic system was stimulated by having subjects actively walk along the track. A helmet-mounted optical system, fixed either on the cart used to provide passive visual or vestibular information or on the walker used in the active walking conditions, provided a stereoscopic display of an optical flow field. Subjects could be positioned at any orientation relative to the heading, and heading judgments were obtained using unimodal visual, vestibular, or walking cues, or combined visual-vestibular and visual-walking cues. Vision alone resulted in reasonably precise and accurate head-pointing judgments (0.3 degrees constant errors, 2.9 degrees variable errors), but not rod-pointing judgments (3.5 degrees constant errors, 5.9 degrees variable errors). Concordant visual-walking stimulation slightly decreased the variable errors and reduced constant pointing errors to close to zero, while head-pointing errors were unaffected.     

Testing the Perrone and Stone (1994) model of heading estimation

Human observers cannot judge heading accurately in the presence of simulated gaze rotations under many conditions [Royden et al. (1994). Vision Research, 34, 3197-3214]. They make errors in the direction of rotation with magnitudes proportional to the rotation rate. Two hypotheses have been advanced to explain this phenomenon. The extra-retinal-signal hypothesis states that the observer's estimate of gaze rotation is always based on an extra-retinal signal such as an efference copy. In the absence of such a signal, the observer assumes that no rotation has taken place and responds accordingly. The retinal-image hypothesis states that visual input dominates when the extra-retinal signal is small or absent; under this hypothesis, errors with simulated rotations are the consequence of faulty visual mechanisms. Perrone and Stone [(1994). Vision Research, 34, 2917-2938] proposed a model that purports to account for these errors using retinal-image information (optic flow) alone; its assumptions make it inefficient under some conditions. The most important of these assumptions is that the fixated target is stationary with respect to the world (the gaze-stabilization constraint). I compared the model's performance to human data from two experiments of Royden et al. [(1994). Vision Research, 34, 3197-3214]. One experiment simulated translation while tracking a target attached to the scene (gaze-stabilized), while the other simulated translation while tracking a target that was not attached (gaze-unstabilized). The incorporation of the gaze-stabilization constraint leads to a predicted asymmetry for the errors in the gaze-unstabilized experiment that is not observed in human data. I conclude that the model as it stands is not consistent with human behavior. It is possible, however, that the predicted asymmetry is masked in human data by a counteracting asymmetry in a hypothetical processing stage subsequent to the heading estimation that extrapolates the observer's future path of self-motion.     

The direct estimation of sound speed using pulse-echo ultrasound

A method for the direct estimation of the longitudinal speed of sound in a medium is presented. This estimator derives the speed of sound through analysis of pulse-echo data received across a single transducer array following a single transmission, and is analogous to methods used in exploration seismology. A potential application of this estimator is the dynamic correction of beamforming errors in medical imaging that result from discrepancy between the assumed and actual biological tissue velocities. The theoretical basis of this estimator is described and its function demonstrated in phantom experiments. Using a wire target, sound-speed estimates in water, methanol, ethanol, and n-butanol are compared to published values. Sound-speed estimates in two speckle-generating phantoms are also compared to expected values. The mean relative errors of these estimates are all less than 0.4%, and under the most ideal experimental conditions are less than 0.1%. The relative errors of estimates based on independent regions of speckle-generating phantoms have a standard deviation on the order of 0.5%. Simulation results showing the relative significance of potential sources of estimate error are presented. The impact of sound-speed errors on imaging and the potential of this estimator for phase aberration correction and tissue characterization are also discussed.     

Use of a priori information in estimating tissue resistivities--a simulation study

Accurate estimation of tissue resistivities in vivo is needed to construct reliable human body volume conductor models in solving forward and inverse bioelectric field problems. The necessary data for the estimation can be obtained by using the four-electrode impedance measurement technique, usually employed in electrical impedance tomography. In this study, a priori geometrical information with statistical properties of regional resistivities and linearization error as well as instrumentation noise has been incorporated into a new resistivity estimation algorithm which is called a statistically constrained minimum mean squares error estimator (MiMSEE) to improve estimation accuracy. MiMSEE intakes geometrical information from the image which is obtained by using a high-resolution imaging modality. This study is an extension of earlier work by Eyübo?lu et al and obtains simulated measurements from two numerical models containing five and six regions on a background region. Also, estimations are repeated by using up to eight multiple current electrode pairs, in order to observe the effect of estimation performance while increasing the number of measurements up to 96. The results are compared with a conventional least squares error estimator (LSEE) which is used in one-pass algorithms. It is shown that the MiMSEE estimation error is up to 27 times smaller than the LSEE error which is realized for a small, high-contrast region, for example the aorta. In estimating the regional resistivities, the MiMSEE algorithm requires 25.8 (for the five-region resistivity distribution) and 22.2 (for the six-region resistivity distribution) times more computational time than the LSEE. This gap between the computational times of the two algorithms decreases as the number of regions increases.     

Product-limit survival functions with correlated survival times

A simple variance estimator for product-limit survival functions is demonstrated for survival times with nested errors. Such data arise whenever survival times are observed within clusters of related observations. Greenwood's formula, which assumes independent observations, is not appropriate in this situation. A robust variance estimator is developed using Taylor series linearized values and the between-cluster variance estimator commonly used in multi-stage sample surveys. A simulation study shows that the between-cluster variance estimator is approximately unbiased and yields confidence intervals that maintain the nominal level for several patterns of correlated survival times. The simulation study also shows that Greenwood's formula underestimates the variance when the survival times are positively correlated within a cluster and yields confidence intervals that are too narrow. Extension to life table methods is also discussed.     

Estimating heading during real and simulated eye movements

The ability to judge heading during tracking eye movements has recently been examined by several investigators. To assess the use of retinal-image and extra-retinal information in this task, the previous work has compared heading judgments with executed as opposed to simulated eye movements. For eye movement velocities greater than 1 deg/sec, observers seem to require the eye-velocity information provided by extra-retinal signals that accompany tracking eye movements. When those signals are not provided, such as with simulated eye movements, observers perceive their self-motion as curvilinear translation rather than the linear translation plus eye rotation being presented. The interpretation of the previous results is complicated, however, by the fact that the simulated eye movement condition may have created a conflict between two possible estimates of the heading: one based on extra-retinal solutions and the other based on retina-image solutions. In four experiments, we minimized this potential conflict by having observers judge heading in the presence of rotations consisting of mixtures of executed and simulated eye movements. The results showed that the heading is estimated more accurately when rotational flow is created by executed eye movements alone. In addition, the magnitude of errors in heading estimates is essentially proportional to the amount of rotational flow created by a simulated eye rotation (independent of the total magnitude of the rotational flow). The fact that error magnitude is proportional to the amount of simulated rotation suggests that the visual system attributes rotational flow unaccompanied by an eye movement to a displacement of the direction of translation in the direction of the simulated eye rotation.     

鲁棒UKF滤波算法在SINS初始对准中的应用

针对系统存在不确定性扰动时传统UKF滤波算法的滤波精度和鲁棒性均下降的问题,提出了一种基于H∞范数的鲁棒UKF滤波算法.该算法在Krein空间内对简化UKF滤波算法进行改进,增加了一个鲁棒环节.鲁棒环节通过引入给定正常数调整滤波增益从而提高滤波算法的鲁棒性能.在SINS大方位失准角初始对准中对简化UKF滤波算法和鲁棒UKF滤波算法进行了对比研究.仿真结果表明:与简化UKF滤波算法相比,鲁棒UKF滤波算法的方位失准角估计误差由16.9'缩小到4.3'.鲁棒UKF滤波算法降低了系统对扰动的敏感度,具有更好的滤波性能.     

Failures to detect moderating effects with ordinary least squares-moderated multiple regression: Some reasons and a remedy.

[Correction Notice: An erratum for this article was reported in Vol 100(2) of Psychological Bulletin (see record 2008-10954-001). Several errors went uncorrected. On page 283, the second line of the first full paragraph should read "in Equation 3...." On page 284, in the eighth line of the first full paragraph, the power in the equation should be "1/2," not "12." On page 287, in Table 4, the heading for column 6 should read "Adjusted SS for deletion of X?X?," not just "X?." The heading for column 7 should read "H?: β?=0c, partial F," not "β?." Finally, in line 3 of the table note, "X?X?" should read "X?,X?."] Describes a means for determining circumstances when ordinary least squares/moderated multiple regression (OLS/MMR) may be at risk in moderator applications and suggests an alternative regression procedure that can be used to overcome the threat of Type II error posed by these circumstances. Using field study data on job satisfaction of employees at state institutions for the developmentally disabled, parallel analyses are presented to show how markedly different results can be obtained between OLS/MMR and the remedial procedure. It is suggested that investigators who have reached conclusions with the traditional OLS/MMR approach reexamine their data. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A computationally simpler algorithm for the UMVUE of a normal mean following a group sequential trial

When using data collected in a group sequential clinical trial, the sample mean is no longer the uniform minimum variance unbiased estimator (UMVUE) of the mean of a normal distribution. Emerson (1993, Computers and Biomedical Research, 26, 68-73) described an algorithm for computing the UMVUE in this setting. This algorithm, although computationally expensive, used only the basic software necessary for deriving group sequential boundaries. In this paper, we present an improved algorithm that results in greatly decreased computation times.     

Estimation of the log-normal mean

The most commonly used estimator for a log-normal mean is the sample mean. In this paper, we show that this estimator can have a large mean square error, even for large samples. Then, we study three main alternative estimators: (i) a uniformly minimum variance unbiased (UMVU) estimator; (ii) a maximum likelihood (ML) estimator; (iii) a conditionally minimal mean square error (MSE) estimator. We find that the conditionally minimal MSE estimator has the smallest mean square error among the four estimators considered here, regardless of the sample size and the skewness of the log-normal population. However, for large samples (n > or = 200), the UMVU estimator, the ML estimator, and the conditionally minimal MSE estimators have very similar mean square errors. Since the ML estimator is the easiest to compute among these three estimators, for large samples we recommend the use of the ML estimator. For small to moderate samples, we recommend the use of the conditionally minimal MSE estimator.     

"Failures to detect moderating effects with ordinary least squares-moderated multiple regression: Some reasons and a remedy": Correction to Morris et al.

Reports an error in "Failures to detect moderating effects with ordinary least squares-moderated multiple regression: Some reasons and a remedy" by James H. Morris, J. Daniel Sherman and Edward R. Mansfield (Psychological Bulletin, 1986[Mar], Vol 99[2], 282-288). Several errors went uncorrected. On page 283, the second line of the first full paragraph should read "in Equation 3...." On page 284, in the eighth line of the first full paragraph, the power in the equation should be "1/2," not "12." On page 287, in Table 4, the heading for column 6 should read "Adjusted SS for deletion of X?X?," not just "X?." The heading for column 7 should read "H?: β?=0c, partial F," not "β?." Finally, in line 3 of the table note, "X?X?" should read "X?,X?." (The following abstract of the original article appeared in record 1986-16215-001.) Describes a means for determining circumstances when ordinary least squares/moderated multiple regression (OLS/MMR) may be at risk in moderator applications and suggests an alternative regression procedure that can be used to overcome the threat of Type II error posed by these circumstances. Using field study data on job satisfaction of employees at state institutions for the developmentally disabled, parallel analyses are presented to show how markedly different results can be obtained between OLS/MMR and the remedial procedure. It is suggested that investigators who have reached conclusions with the traditional OLS/MMR approach reexamine their data. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of translational heading from optical flow.

Radial patterns of optical flow produced by observer translation could be used to perceive the direction of self-movement during locomotion, and a number of formal analyses of such patterns have recently appeared. However, there is comparatively little empirical research on the perception of heading from optical flow, and what data there are indicate surprisingly poor performance, with heading errors on the order of 5°–20°. We examined heading judgments during translation parallel, perpendicular, and at oblique angles to a random-dot plane, varying observer speed and dot density. Using a discrimination task, we found that heading accuracy improved by an order of magnitude, with 75%-correct thresholds of 0.66° in the highest speed and density condition and 1.2° generally. Performance remained high with displays of 63–20 dots, but it dropped significantly with only 2 dots; there was no consistent speed effect and no effect of angle of approach to the surface. The results are inconsistent with theories based on the local focus of outflow, local motion parallax, multiple fixations, differential motion parallax, and the local maximum of divergence. But they are consistent with Gibson's (1950) original global radial outflow hypothesis for perception of heading during translation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Predicting student attitudes about racial diversity and gender equity.

[Correction Notice: An erratum for this article was reported in Vol 4(3) of Journal of Diversity in Higher Education (see record 2011-16523-001). There are two errors in Table 2 under the RWA heading and the Cog-gender heading. The necessary changes are provided in the erratum.] [Correction Notice: An erratum for this article was reported in Journal of Diversity in Higher Education on August 1 2011 (see record 2011-16523-001). There are two errors in Table 2. Under the RWA heading, the SDO row should have indicated a positive correlation of .266**, not -.266**. Under the Cog-gender heading, the SDO row should have indicated a negative correlation of -.438**, not .438**.] Factors related to attitudes about racial diversity and gender equity were examined in an ethnically diverse sample of 432 college students (167 European Americans, 83 African Americans, 81 Asian Americans, and 82 Hispanic Americans). In addition to variables of self-interest (i.e., ethnicity, gender, and political views), social ideology (i.e., social dominance orientation, right-wing authoritarianism) and personality traits (openness to experience) were uniquely predictive of attitudes about racial diversity and gender equity. Hierarchical regressions revealed that social dominance orientation most strongly predicted racial attitudes, while right-wing authoritarianism most strongly predicted gender attitudes. Implications for diversity education efforts related to prejudice reduction are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The structure and function of yeast xylose (aldose) reductases

In three dimensional (3-D) human movement analysis using close-range photogrammetry, surface marker clusters deform and rigidly move relative to the underlying bone. This introduces an important artefact (skin movement artefact) which propagates to bone position and orientation and joint kinematics estimates. This occurs to the extent that those joint attitude components that undergo small variations result in totally unreliable values. This paper presents an experimental and analytical procedure, to be included in a subject-specific movement analysis protocol, which allows for the assessment of skin movement artefacts and, based on this knowledge, for their compensation. The effectiveness of this procedure was verified with reference to knee-joint kinematics and to the artefacts caused by the hip movements on markers located on the thigh surface. Quantitative validation was achieved through experimental paradigms whereby prior reliable information on the target joint kinematics was available. When position and orientation of bones were determined during the execution of a motor task, using a least-squares optimal estimator, but the rigid artefactual marker cluster movement was not dealt with, then knee joint translations and rotations were affected by root mean square errors (r.m.s.) up to 14 mm and 6 degrees, respectively. When the rigid artefactual movement was also compensated for, then r.m.s errors were reduced to less than 4 mm and 3 degrees, respectively. In addition, errors originally strongly correlated with hip rotations, after compensation, lost this correlation.     

Enhanced EM-based channel estimation for MIMO-OFDM in highly mobile channels

An enhanced expectation-maximization (EM)-based iterative channel estimator for coping with channel time variation is proposed for mobile multiple-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems.In the proposed scheme,the recursive least squares (RLS) algorithm is applied to track the time-varying channel impulse response (CIR) within several symbols.By using the tracked time-varying CIR,the ICI are constructed and then cancelled from the received signal,thus reducing their impactions on the channel estimation.Moreover,based on an ovet-sampled complex exponential basis expansion model (OCE-BEM),an improved channel predictor is derived in order to improve the initial channel estimates accuracy of the iterative estimator.Simulation results show that the proposed scheme outperforms the classic counterpart in time-varying scenarios with a smaller cost of complexity.     

Magnetic characteristics of Ya?argil aneurysm clips

BACKGROUND: Metallic bioimplants are subject to great scrutiny in order to ensure that they are totally harmless to patients. Aneurysm clips are no exception to this rule. Considering the number of aneurysm clips used and their potential for injury, they should be evaluated very meticulously. Determining the magnetic characteristics of these clips is an important part of the evaluation process. In this study, a new method for evaluating magnetism is described and the importance of that information is briefly discussed. METHODS: Twenty Ya?argil aneurysm clips were analyzed using a vibrating sample magnetometer under 1.5 Tesla. This device is highly sensitive, and is capable of measuring the magnetism of small objects. RESULTS: Our measurements showed magnetism of the aneurysm clips ranged from 0.0334-0.1369 electromagnetic units (emu). CONCLUSIONS: Magnetometer measurements and real life tests under magnetic resonance imaging (MRI) have shown that these clips have a very low magnetism and are safe to use in 1.5 Tesla MRI scanners. This study also proves that the vibrating sample magnetometer is a useful device for analyzing the magnetism of aneurysm clips, and their emu values can be used as another industry standard in the production line to increase the safety of these clips.     

Wild-type Flp recombinase cleaves DNA in trans

Site-specific recombinases of the Integrase family utilize a common chemical mechanism to break DNA strands during recombination. A conserved Arg-His-Arg triad activates the scissile phosphodiester bond, and an active-site tyrosine provides the nucleophile to effect DNA cleavage. Is the tyrosine residue for the cleavage event derived from the same recombinase monomer which provides the RHR triad (DNA cleavage in cis), or are the triad and tyrosine derived from two separate monomers (cleavage in trans)? Do all members of the family follow the same cleavage rule, cis or trans? Solution studies and available structural data have provided conflicting answers. Experimental results with the Flp recombinase which strongly support trans cleavage have been derived either by pairing two catalytic mutants of Flp or by pairing wild-type Flp and a catalytic mutant. The inclusion of the mutant has raised new concerns, especially because of the apparent contradictions in their cleavage modes posed by other Int family members. Here we test the cleavage mode of Flp using an experimental design which excludes the use of the mutant protein, and show that the outcome is still only trans DNA cleavage.     

A general approach for estimating scale score reliability for panel survey data.

Scale score measures are ubiquitous in the psychological literature and can be used as both dependent and independent variables in data analysis. Poor reliability of scale score measures leads to inflated standard errors and/or biased estimates, particularly in multivariate analysis. Reliability estimation is usually an integral step to assess data quality in the analysis of scale score data. Cronbach’s α is a widely used indicator of reliability but, due to its rather strong assumptions, can be a poor estimator (L. J. Cronbach, 1951). For longitudinal data, an alternative approach is the simplex method; however, it too requires assumptions that may not hold in practice. One effective approach is an alternative estimator of reliability that relaxes the assumptions of both Cronbach’s α and the simplex estimator and thus generalizes both estimators. Using data from a large-scale panel survey, the benefits of the statistical properties of this estimator are investigated, and its use is illustrated and compared with the more traditional estimators of reliability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociable mechanisms of subitizing and counting: Neuropsychological evidence from simultanagnosic patients.

Do people have to count to determine visual numerosity, or is there a fast "subitizing" procedure dedicated to small sets of 1 to 3 items? Numerosity naming time and errors were measured in 5 simultanagnosic patients who suffered from severe difficulties in serial counting. Although these patients made close to 100% errors in quantifying sets comprising more than 3 items, they were excellent at quantifying sets of 1, 2, and sometimes 3 items. Their performances in visual search tasks suggested that they suffered from a deficit of serial visual exploration, due to a fundamental inability to use spatial tags to keep track of previously explored locations. The present data suggest that the patients' preserved subitizing abilities were based not on serial processing but rather on a parallel algorithm dedicated to small numerosities. Several ways in which this parallel subitizing algorithm might function are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognition of facial stimuli following an intervening task involving the Identi-kit.

The Identi-kit is a tool for constructing a facial composite. The types of errors made on a recognition task, following an intervening task involving the Identi-kit, were examined in this study. One hundred and eight introductory psychology students viewed a target composite-face and made an Identi-kit reconstruction. Subsequently, they were required to identify the original composite-face from a lineup of six composite-faces. Subjects who made an Identi-kit reconstruction were prone to make more errors on the recognition task than participants in a control condition, p?p?p?