The contribution of vision and proprioception to judgements of finger proximity

We sought to determine whether an increase in judged egocentric distance created by increasing vergence-specified distance would be negated when participants pointed at their own finger. It was found that ocular position dominates limb proprioception in the judgement of finger distance in the sagittal plane when vision is available. In contrast, an increase in perceived egocentric distance was largely attenuated by the presence of limb proprioception in reduced visual cue conditions. We conclude that the relative contribution of vergence to perceived distance depends upon the strength of the vergence effort signal when there are other cues present. Furthermore, if the distance percept includes a major contribution from retinal cues, then the visual component will dominate the limb proprioception component. If the visual component is largely determined by vergence information, limb proprioception will make a significant contribution and actually dominate when the vergence effort signal is weak. The results extend previous studies that have found a similar relationship between ocular position and limb proprioception in the perception of a finger′s location in the coronal plane.     

The mechanics of running while approaching and jumping over an obstacle

When leaping an obstacle, the runner increases the vertical velocity of his/her centre of mass (COM) at takeoff to augment the amplitude and duration of the aerial phase over it. This study analyses the modification of the bouncing mechanism of running when approaching a barrier. The forces exerted by the feet on the ground are measured by a 13-m-long force platform during the four to nine running steps preceding the jump over a 0.45- to 0.85-m-high barrier, at an approaching speed between 9 and 21 km h^?1. The movements of the COM are evaluated by time-integration of the forces and the stiffness of the bouncing system by computer simulation. The running mechanism is modified during the two steps preceding the barrier. During the contact period, two steps before the barrier, the leg-spring stiffness decreases; consequently, the COM is lowered and accelerated forward. Then during the contact period preceding the obstacle, the leg-spring stiffness increases and the COM is raised and accelerated upwards, whereas its forward velocity is reduced. During this phase, the leg-spring acts like a pole, which stores elastic energy and changes the direction of the velocity vector to release this energy in a vertical direction. At high speeds, this storage–release mechanism of elastic energy is sufficient to provide the energy necessary to leap the obstacle. On the contrary, at low speeds, the amount of elastic energy stored and released in the leg-spring is not sufficient to jump over the obstacle and additional positive muscular work must be done.     

Afferent input, efference copy, signal noise, and biases in perception of joint angle during active versus passive elbow movements

Psychophysical studies have reported an overestimation of limb position in the direction of movement during the early part of active movements. The main hypothesis tested in this study is that the overestimation results from a process of forward prediction of limb state driven by an efference copy of the outgoing motor command. This hypothesis predicts that position overestimation should decrease or disappear during passive movements, for which there should be no efference copy. Seven subjects were asked to remember and to report the perceived angle of their elbow joint at different times during active and passive movements. They showed a highly velocity-dependent overestimation of the elbow joint angle near the beginning of the movement in both active and passive trials. Toward the end of the movement, subjects showed a relatively velocity-independent underestimation of their elbow angle in all trials. Contrary to the prediction of the efference copy hypothesis, the amplitude and the velocity-dependent slope of the elbow angle overestimation were both greater during the early part of passive movements than active movements. This indicates that psychophysical evidence of early overestimation of arm position on its own is not a sufficient proof of forward prediction based on an efference copy, at least under the conditions of this study. Decreased errors during active movements suggest that an efference copy can improve the accuracy of state estimation during active movements. Error patterns seem to parallel the likely level of sensorimotor noise, suggesting a probabilistic mechanism for position estimation.     

Long-lasting aftereffect of a single prism adaptation: shifts in vision and proprioception are independent

After a single adaptation session to prisms with gradually incremented shift magnitude, the prism adaptation aftereffect was measured by open loop mid-sagittal pointing (O) to a visual target without visual feedback. This aftereffect corresponded to the summation of the shift in proprioception, measured by straight ahead pointing without vision (S), and the visual straight ahead judgement (V), measured by verbal stopping of an LED moving from two opposite directions. However, the measurement of the aftereffects made over a period of 7 days revealed significantly different decay curves in V, O and S. Surprisingly the S shift was still present up to 7 days after the training, while V had returned to the original level by 2 h, which was the first measurement after subjects returned to a normal visual environment. O had returned to pre-test level after 1 day. After 3 days Wilkinson’s (J Exp Psychol 89:250–257, 1971) additive hypothesis (O=S−V) no longer fit the data. Rather “O=Pl−V”, where Pl (Pr) is the shift in proprioception measured by passive lateral arm movements from left (right), fitted better during the whole 7 days of aftereffect in our study. Therefore, the aftereffect of our strong prism adaptation revealed, firstly, that classical open loop pointing consisted of aftereffect shifts equal to the summation of the shifts in the two passively measurable aftereffect components, vision (V) and proprioception (Pl), rather than with active straight ahead pointing (S). Secondly, the decay of the shift in visual perception and in passively measurable proprioception is independent. The former decays fast, and the latter decays slowly with two separate waves. Thirdly, we suggest that the use of visual perception-dependent spatial codes for visual-manual transformation and the vision-independent internal egocentric reference frame are mutually exclusive. We proposed a model to explain these possible mechanisms.     

The contribution of apolipoprotein E alleles on cognitive performance and dynamic neural activity over six decades

Neuroimaging shows brain-functional differences due to apolipoprotein E (APOE) polymorphisms may exist decades before the increased risk period for Alzheimer's disease, but little is known about their effect on cognition and brain function in children and young adults. This study assessed 415 healthy epsilon2 and epsilon4 carriers and matched epsilon3/epsilon3 controls, spanning ages 6-65, on a range of cognitive tests. Subjects were also compared on a new dynamical measure of EEG activity during a visual working memory task using alphabetical stimuli. epsilon4 subjects had better verbal fluency compared to epsilon3, an effect that was strongest in 51-65 year-olds. No epsilon4 deficits in cognition were found. In 6-15 year-olds, there were differences in total spatio-temporal wave activity between epsilon3 and epsilon4 subjects in the theta band, approximately 200ms post-stimulus. Differences in brain function in younger epsilon4 subjects and superior verbal fluency across the entire age range suggest that the APOE epsilon4 allele is an example of antagonistic pleiotropy.     

Stepping over an obstacle on a compliant travel surface reveals adaptive and maladaptive changes in locomotion patterns

Adaptive human locomotion is dependent on safe clearance of obstacles encountered in the path of locomotion. When the terrain is uneven or compliant, stability along with safe obstacle clearance are competing demands presented to the central nervous system (CNS). To examine how the CNS deals with the two competing demands, six participants walked under four conditions: normal ground walking, normal ground walking with an obstacle in the travel path, compliant surface walking, and compliant surface walking with an obstacle in the travel path. Full body kinematics were measured and swing limb kinetics were derived from these measurements. Results showed that on a compliant surface, the CNS was able to decrease foot placement variability at foot contact when approaching an obstacle, similar to the normal ground terrain. Limb trajectory over the obstacle showed that toe elevation was maintained while clearance over the obstacle was lower in the compliant surface condition due to depression of the surface during push off. This illustrates that the CNS controls toe elevation, not toe clearance when stepping over an obstacle. Work done in the knee during elevation and hip during lowering was similar in the compliant and ground conditions even though a lower clearance over the obstacle was achieved in the complaint condition. This shows the inability of the CNS to account for compression of the surface prior to obstacle clearance and provides further evidence the CNS controls toe elevation, not clearance when stepping over an obstacle.An erratum to this article can be found at     

The mechanics of jumping over an obstacle during running: a comparison between athletes trained to hurdling and recreational runners

Purpose

This study compares the mechanism of running in trained athletes (TA) experienced in hurdling and in recreational runners (RR), as they approach and jump over an obstacle.

Methods

The movements of the centre of mass of the body (COM), the external muscular work (W _ext) and the leg-spring stiffness (k _leg) were evaluated in athletes approaching an obstacle at 18 km h^?1, from the ground reaction forces (measured by force-platforms) and the orientation of the lower-limb segments (measured by camera). These results were compared to those obtained in RR.

Results

Two steps before the obstacle, k _leg is reduced by 10–20 %; so, the COM is lowered and accelerated forward. During the step preceding the obstacle, k _leg is increased by 40–60 %; so the COM is raised and accelerated upwards, whereas its forward velocity is reduced. This change in the running pattern is similar to the one observed in RR while leaping an obstacle. However, in TA, the change in stiffness is less pronounced. As a result, the orientation of the velocity vector at the beginning of the aerial phase over the obstacle is more horizontal than in RR, which involves a 10–20 % greater horizontal velocity and a 40–60 % smaller vertical excursion of the COM when crossing the obstacle; subsequently, W _ext during contact before the obstacle is 10–20 % less.

Conclusion

Athletes use the same mechanisms as non-specialists to cross an obstacle. However, athletes adapt the mechanism of jumping to reduce the loss in the velocity of progression when crossing an obstacle.     

The role of proprioception and attention in a visuomotor adaptation task

The role of proprioception in the control and adaptation of visuomotor relationships is still unclear. We have studied a deafferented subject, IW, and control subjects in a task in which they used single joint elbow extension to move to a visual target, with visual feedback of the terminal position provided by a cursor displayed in the plane of their movements. We report the differences in movement accuracy between the deafferented subject and controls in the normal task and when challenged with a cognitive load, counting backwards. All subjects were less accurate when counting; this was a small effect for the controls (<10% change) but much greater for the deafferented subject (>60% change). We also examined changes in movement kinematics when the instructed amplitude was altered via a changed gain between final arm position and presentation of the feedback cursor. The deafferented subject maintained temporal movement parameters stable and altered amplitude by scaling force (i.e. changed peak velocity), whereas the controls scaled both movement velocity and duration. Finally, we compared the subjects' adaptation of movement amplitude after a period of exposure to the changed visuomotor gain. The deafferented subject was able to adapt, but his adaptation was severely impaired by the counting task. These results suggest that proprioception is not an absolute requirement for adaptation to occur. Instead, proprioception has a more subtle role to play in the adjustment to visuomotor perturbations. It has an important role in the control of reaching movements, while in the absence of proprioception, attention appears necessary to monitor movements.     

A Judd illusion in far-aiming: evidence of a contribution to action by vision for perception

The present study addresses the role of vision for perception in determining the location of a target in far-aiming. Participants (N = 12) slid a disk toward a distant target embedded in illusory Judd figures. Additionally, in a perception task, participants indicated when a moving pointer reached the midpoint of the Judd figures. The number of hits, the number of misses to the left and to the right of the target, the sliding error (in mm) and perceptual judgment error (in mm) served as dependent variables. Results showed an illusory bias in sliding, the magnitude of which was comparable to the bias in the perception of target location. The determination of target location in far-aiming is thus based on relative metrics. We argue that vision for perception sets the boundary constraints for action and that within these constraints vision for action autonomously controls movement execution, but alternative accounts are discussed as well.

The effects of distant and on-line visual information on the control of approach phase and step over an obstacle during locomotion

One of the goals of this study was to examine the nature and role of distant visual information sampled during locomotion in the feedforward control of leading and trailing limb while an individual is required to step over an obstacle in the travel path. In addition we were interested in whether or not on-line visual information available while the limb (lead or trail) is stepping over the obstacle influences limb trajectory control and whether the information provided during lead limb cross would be used to calibrate movement of the trail limb. Towards this end, we manipulated availability of vision following an initial dynamic sampling period during the approach phase in proximity to the obstacle and during the lead and trail limb stepping over the obstacle. Ten participants completed 40 trials of obstacle crossing in 8 testing conditions. Initial dynamic visual sampling was sufficient to ensure successful task performance in the absence of vision in the approach phase and during both lead and trail limb stepping over the obstacle. Despite successful task performance, foot placement of the lead and trail limb before obstacle crossing and limb elevation over the obstacle were increased after withdrawal of vision in the approach area. Furthermore, the correlation between toe clearance and foot placement was diminished. While both limbs require feedforward visual information to control the step over the obstacle, only lead limb elevation was influenced by availability of on-line visual information during obstacle crossing. Results were in agreement with the notion of primacy of information inherent in the optic array over those from static samples of the environment in guiding locomotion. It is suggested that the expected proprioceptive feedback information associated with the limb posture before the obstacle, reconstructed using visual memory from dynamic sampling of the environment, mismatched with those from the actual limb position. Accordingly, participants adopted a different strategy that enabled them to clear the obstacle with a higher safety margin.Financial assistance was provided by a grant from the Office of Naval Research, USA, NSERC/Canada, and CAPES/Brazil. We would like to thank Milad G. Ishac, Mike Greig, Zinat Shafaei-Shirazi, and Candida T. Goncalves for their assistance     

Adaptation of a foot plate for use in an isokinetic and isotonic leg press

The use of isokinetic equipment and the leg press exercise have been major components of rehabilitation for the past several years when redeveloping muscular strength. Recently, closed kinetic chain exercises have been shown to be more beneficial and have less adverse affects on the knee when rehabilitating a patient's lower extremity. The purpose of this article is to introduce the leg press foot plate to the rehabilitative community. This foot plate is a versatile piece of equipment that has been adapted for use with various isokinetic, isometric, and isotonic devices in order to do leg press exercises. The device allows for closed kinetic chain strengthening and testing from equipment typically used only for open kinetic chain activities.     

The differential contribution of mental tracking,cognitive flexibility,visual search,and motor speed to performance on parts A and B of the trail making test

Ninety-eight undergraduate students were subjected to the TMT as well as a series of derived measures from the TMT with a view to ascertaining the nature of the contribution of each to the performance. Performance on the TMT(A) was uniquely contributed to by visual search and motor speed measures, whereas the performance on TMT(B) was uniquely contributed to by the visual search and cognitive alternation measures. After controlling for the effects of TMT(A) on TMT(B), further variance in the score on TMT(B) was contributed to, in order of effect, by lowered reading level, poor skill in visual search, poor ability to mentally maintain two simultaneous sequences, as well as decrease in attention and working memory functions. The analysis indicates that, in a nonclinical sample, the TMT measures a number of different functions and the observation of impaired performance must be further investigated to ascertain the specific nature of these deficits in order to guide rehabilitation and management planning. © 1998 John Wiley & Sons, Inc. J Clin Psychol 54: 585–591, 1998.     

More than a neuroanatomical representation in The Creation of Adam by Michelangelo Buonarroti,a representation of the Golden Ratio

Michelangelo Buonarroti (1475–1564) was a master anatomist as well as an artistic genius. He dissected numerous cadavers and developed a profound understanding of human anatomy. Among his best‐known artworks are the frescoes painted on the ceiling of the Sistine Chapel (1508–1512), in Rome. Currently, there is some debate over whether the frescoes merely represent the teachings of the Catholic Church at the time or if there are other meanings hidden in the images. In addition, there is speculation regarding the image of the brain embedded in the fresco known as “The Creation of Adam,” which contains anatomic features of the midsagittal and lateral surfaces of the brain. Within this context, we report our use of Image Pro Plus Software 6.0 to demonstrate mathematical evidence that Michelangelo painted “The Creation of Adam” using the Divine Proportion/Golden Ratio (GR) (1.6). The GR is classically associated with greater structural efficiency and is found in biological structures and works of art by renowned artists. Thus, according to the evidence shown in this article, we can suppose that the beauty and harmony recognized in all Michelangelo's works may not be based solely on his knowledge of human anatomical proportions, but that the artist also probably knew anatomical structures that conform to the GR display greater structural efficiency. It is hoped that this report will at least stimulate further scientific and scholarly contributions to this fascinating topic, as the study of these works of art is essential for the knowledge of the history of Anatomy. Clin. Anat. 28:702–705, 2015. © 2015 Wiley Periodicals, Inc.     

The epidemiology of Graves' disease: Evidence of a genetic and an environmental contribution

Previous family and twin studies have indicated that Graves' disease has a heritable component. Family studies have also shown that some autoimmune disease cluster in families and genetic studies have been able to show shared susceptibility genes. In the present nation-wide study we describe familial risk for Graves' disease among parents and offspring, singleton siblings, twins and spouses with regard to age of onset, gender and number and type of affected family members. Additionally familial association of Graves' disease with any of 33 other autoimmune and related conditions was analyzed. The Swedish Multigeneration Register on 0–75-year-old subjects was linked to the Hospital Discharge Register from years 1987–2007. Standardized incidence ratios (SIRs) were calculated for individuals whose relatives were hospitalized for Graves' disease compared to those whose relatives were unaffected. The total number of hospitalized Graves' patients was 15,743. Offspring with an affected family member constituted 3.6% of all patients among offspring. The familial SIR was 5.04 for individuals whose sibling was affected but it increased to 310 when two or more siblings were affected; the SIR in twins was 16.45. Familial risks were higher for males than for females. The SIR was increased to 6.22 or 30.20 when parental age was limited to 50 or 20 years, respectively. Graves' disease associated with 19 other autoimmune and related conditions, including Addison's disease, type 1 diabetes mellitus, Hashimoto/hypothyroidism, pernicious anemia, polymyositis/dermatomyositis, myasthenia gravis, discoid lupus erythematosus and localized scleroderma. Remarkably, there was a high disease concordance of 2.75 between spouses. The clustering between spouses suggests environmental effects on Graves' disease which may contribute to the observed gender effects. The demonstrated high risks should be considered in clinical counseling and in prevention plans.     

SgD-CNV, a database for common and rare copy number variants in three Asian populations

Copy number variants (CNVs) extend our understanding of the genetic diversity in humans. However, the distribution and characteristics of CNVs in Asian populations remain largely unexplored, especially for rare CNVs that have emerged as important genetic factors for complex traits. In the present study, we performed an in-depth investigation of common and rare CNVs across 8,148 individuals from the three major Asian ethnic groups: Chinese (n = 1,945), Malays (n = 2,399), and Indians (n = 2,217) in Singapore, making this investigation the most comprehensive genome-wide survey of CNVs outside the European-ancestry populations to date. We detected about 16 CNVs per individual and the ratio of loss to gain events is ～2:1. The majority of the CNVs are of low frequency (<10%), and 40% are rare (<1%). In each population, ～20% of the CNVs are not previously catalogued in the Database of Genomic Variants (DGV). Contrary to findings from European studies, the common CNVs (>5%) in our populations are not well tagged by SNPs in Illumina 1M and 610K arrays, and most disease-associated common CNVs previously reported in Caucasians are rare in our populations. We also report noticeable population differentiation in the CNV landscape of these Asian populations, with the greatest diversity seen between the Indians and the Chinese.     

Reductions in turnover,accidents, and absenteeism: The contribution of a pre-employment screening inventory

This study examined the rates of turnover, work-related accidents, and unauthorized absence among two contrasted groups of employees in a midsized manufactoring environment. For the calendar year 1989, comparative rates on each variable were obtained for a group hired prior to the inclusion of a pre-employment inventory in the Company's selection process and a group hired subsequently. Results indicate that rates of turnover, accidents, and unauthorized absence were all significantly lower in the group hired subsequent to inclusion of the pre-employment screening inventory. Some possible design artifacts and cost-benefit implications are discussed.     

A dynamometer for the measurement of force,velocity, work and power during an explosive leg extension

Summary A dynamometer for measurement under static and dynamic conditions is presented. At different load levels, force, velocity, work and power can be measured in explosive leg extensions. Measurements on 53 subjects at different load levels (0–125.5 kg) were carried out. Peak power ranged from 2611 to 1746 W, force from 1351 to 1899 N, velocity from 1.61 to 0.89 m·s⁻¹ and work from 329 to 605 J. Between trial correlation coefficients ranged from 0.72 to 0.95. The dynamometer is compared with others, and it is concluded that data obtained by this dynamometer have a greater practical validity.     

The role of active forces and intersegmental dynamics in the control of limb trajectory over obstacles during locomotion in humans

The focus of this paper is to examine the contributions of active and passive forces in the control of limb trajectory over obstacles during locomotion. Kintetic analyses of the swing phase of locomotion were carried out to determine the power profiles at various joints and to parcel the joint moments into moments due to muscle action, gravitational force and motion-dependent terms. The analyses revealed that toe elevation over the obstacles was achieved primarily by flexing at the hip, knee and ankle joint. Power analyses showed that translational energy applied at the hip joint and rotational energy applied at the knee joint were modulated as functions of obstacle height. This demonstrates that increased hip and ankle joint flexion are achieved not through active muscle action but rather through passive forces induced by translational action at the hip (representing contribution by the stance limb muscles) and rotational action at the knee joint. Parcelling the joint moment terms into various components clearly shows how the nervous system exploits intersegmental dynamics to simplify control of limb elevation over obstacles and minimize energy costs.     

Object representation and distance encoding in three-dimensional environments by a neural circuit in the visual system of the blowfly

Three motion-sensitive key elements of a neural circuit, presumably involved in processing object and distance information, were analyzed with optic flow sequences as experienced by blowflies in a three-dimensional environment. This optic flow is largely shaped by the blowfly's saccadic flight and gaze strategy, which separates translational flight segments from fast saccadic rotations. By modifying this naturalistic optic flow, all three analyzed neurons could be shown to respond during the intersaccadic intervals not only to nearby objects but also to changes in the distance to background structures. In the presence of strong background motion, the three types of neuron differ in their sensitivity for object motion. Object-induced response increments are largest in FD1, a neuron long known to respond better to moving objects than to spatially extended motion patterns, but weakest in VCH, a neuron that integrates wide-field motion from both eyes and, by inhibiting the FD1 cell, is responsible for its object preference. Small but significant object-induced response increments are present in HS cells, which serve both as a major input neuron of VCH and as output neurons of the visual system. In both HS and FD1, intersaccadic background responses decrease with increasing distance to the animal, although much more prominently in FD1. This strong dependence of FD1 on background distance is concluded to be the consequence of the activity of VCH that dramatically increases its activity and, thus, its inhibitory strength with increasing distance.