Antihysteresis of perceived longitudinal body axis during continuous quasi-static whole-body rotation in the earth-vertical roll plane

Estimation of subjective whole-body tilt in stationary roll positions after rapid rotations shows hysteresis. We asked whether this phenomenon is also present during continuous quasi-static whole-body rotation and whether gravitational cues are a major contributing factor. Using a motorized turntable, 8 healthy subjects were rotated continuously about the earth-horizontal naso-occipital axis (earth-vertical roll plane) and the earth-vertical naso-occipital axis (earth-horizontal roll plane). In both planes, three full constant velocity rotations (2°/s) were completed in clockwise and counterclockwise directions (acceleration = 0.05°/s², velocity plateau reached after 40 s). Subjects adjusted a visual line along the perceived longitudinal body axis (pLBA) every 2 s. pLBA deviation from the longitudinal body axis was plotted as a function of whole-body roll position, and a sine function was fitted. At identical whole-body earth-vertical roll plane positions, pLBA differed depending on whether the position was reached by a rotation from upright or by passing through upside down. After the first 360° rotation, pLBA at upright whole-body position deviated significantly in the direction of rotation relative to pLBA prior to rotation initiation. This deviation remained unchanged after subsequent full rotations. In contrast, earth-horizontal roll plane rotations resulted in similar pLBA before and after each rotation cycle. We conclude that the deviation of pLBA in the direction of rotation during quasi-static earth-vertical roll plane rotations reflects static antihysteresis and might be a consequence of the known static hysteresis of ocular counterroll: a visual line that is perceived that earth-vertical is expected to be antihysteretic, if ocular torsion is hysteretic.     

Visually guided reaching for food in binocularly deprived cats.

Four visually deprived cats and four controls were tested in reaching for food from a cage. In each trial the animals in the groups responded immediately after unscreening the cage. However, in reaction time of forelimb extension the deprived group showed proportionally fewer responses with shorter reaction time than the control group.     

Visually guided reaching in the cat reared in fixed or random frequency stroboscopic light

The effect of deprivation of visual perception of movement in a visuo-motor task has been tested in cats reared in stroboscopic light since birth. Three cats were reared in light of fixed (2 flash/sec, flash duration 2 msec) and three in light of random (between 0.5 and 3.5 flash/sec) frequency. These 6 animals, together with 6 control cats, underwent (as adults) a test of visual control of reaching for a target with a paw, with operant conditioning. While the cats raised in fixed frequency stroboscopic conditions (FFS) showed no deficit, those raised in random frequency condition (RFS) exhibited significantly less precise guidance than FFS and control animals.     

Visually guided stepping under conditions of step cycle-related denial of visual information

We recently reported that subjects performing a task that requires visual guidance of each step onto irregularly placed stepping stones usually fixate the next target of footfall just before they lift the foot to be repositioned, i.e. towards the end of that limb's stance phase. When negotiating the same walkway without ambient lighting, and with each stone's location indicated by a central light spot (LED), stepping and eye movements were unchanged. Under conditions of intermittent visual denial, in which all LEDs (the only visual cues) were temporarily extinguished at irregular intervals, temporal changes in the normal stepping pattern were sometimes observed, but stepping was not always affected. The primary effect of visual denial was on the leg that was in stance (foot in place on a stepping stone) at the moment of LED extinction, rather than on the leg that was in swing, and was an increase in stance duration, suggesting an effect on planning during this stance of the next swing towards the next target rather than on execution of the ongoing swing of the other leg. Subjects rarely failed to step onto the targets. Prolongations of stance under visual denial lasting 400 or 500 ms were less than 200 ms, much less than the duration of denial; subjects did not simply wait for the footfall target to reappear. There was no effect for denial lasting 300 ms; subjects performed as well as with a constantly visible target. Under 400 and 500 ms denial, there was no effect when the targets disappeared in the first 100 ms of stance (of the foot to be repositioned); stance durations were indistinguishable from control. This suggests that there is no crucial visuomotor processing by the control system(s) for eye and limb guidance until the target reappeared near the usual end of stance, when feedforward planning of the next saccade and/or swing to a target reaches a crucial stage, and is affected by intrusion of the period of visual denial. With longer (800 ms) denial there was an effect regardless of when in stance it began. A smaller effect of 800 ms denial sometimes visible in swing duration is attributable to interlimb coordination. Accurate saccades, followed by accurate steps, to the next target are almost always made, even when the target is invisible. Our results demonstrate that uninterrupted on-line visual information is not necessary for accurate stepping even when (as here) each step requires visual guidance. Also, since stance prolongations did not always result, and they were always much shorter than the periods of denial, we conclude that the visuomotor control mechanism(s) are robust in the face of substantial denial of all visual information including normally preferred inputs (foveal or peripheral images) at the normally preferred times. The fact that a saccade is still made to an invisible target location implies that this is useful in itself, since it does not result in a visible foveal image. We propose that skilled, visually guided stepping onto irregularly placed targets is executed under predominantly feedforward visuomotor control mechanisms, and suggest that the ability to function effectively in this way is dependent upon the integrity of the lateral cerebellum.     

Linear acceleration perception in the roll plane before and after unilateral vestibular neurectomy

Summary The ability of 33 patients to perceive the direction, relative to the body long axis, of a linear acceleration vector acting in the coronal plane, rolltilt perception, was studied at various times, before and from 1 week to 6 months after unilateral, selective vestibular neurectomy for Meniere's disease, acoustic neuroma or intractable paroxysmal vertigo. The results of these patients were compared with the results of 31 normal subjects and two control patients who had both vestibular nerves surgically sectioned. Rotating on a fixed-chair centrifuge in an otherwise darkened room, each observer was required to indicate his perception of the direction of the resultant gravito-inertial vector by setting a small, motor-driven, illuminated bar, attached to the chair but rotatable in the frontoparallel plane, to the perceived gravitational horizontal. Normal subjects accurately align the bar with respect to the gravito-inertial resultant vector which, in the dark, they assume to be the gravitational vertical. This percept has been called the oculogravic illusion. Accurate roll-tilt perception is due to vestibular (probably mainly otolithic) sensory information since patients with bilateral vestibular neurectomies do not perceive the resultant vector accurately. Whereas normal subjects perceive resultant vectors directed to the right and to the left equally accurately, roll-tilt perception was invariably asymmetrical one week after unilateral vestibular neurectomy. Even at rest there was an asymmetry in the baseline settings, so that patients set the bar down on the side of the operated ear, in order for it to appear gravitationally horizontal: if a patient had a right vestibular nerve section then he set the bar clockwise (from the patient's view) below the true gravitational horizontal. With increasing gravitoinertial resultant angles there was an increasing asymmetry of roll-tilt perception due both to decreased sensitivity to roll-tilt stimuli directed towards the operated ear and to transiently increased sensitivity to roll-tilt stimuli directed towards the intact ear. A progressive decrease in both perceptual asymmetries followed, rapidly in the first 3 weeks, more slowly in the next 6 months. Based on these results, which are consistent with what is known about the responses of primary and secondary otolithic neurons to linear acceleration, we propose: (1) that the asymmetric roll-tilt perceptual response following unilateral vestibular neurectomy is an otolithic analogue of Ewald's second law; (2) that the perceptual asymmetries may be due to decreased spontaneous activity in the deafferented lateral vestibular nucleus; (3) that the progressive recovery of roll-tilt perceptual symmetry after vestibular neurectomy may be part of the otolithic component of the total recovery phenomenon known as vestibular compensation; (4) that ocular torsion caused by the unilateral vestibular neurectomy is a major factor contributing to the systematic errors in baseline settings to the gravitational horizontal one week after operation.     

Visually guided grasping produces fMRI activation in dorsal but not ventral stream brain areas

Although both reaching and grasping require transporting the hand to the object location, only grasping also requires processing of object shape, size and orientation to preshape the hand. Behavioural and neuropsychological evidence suggests that the object processing required for grasping relies on different neural substrates from those mediating object recognition. Specifically, whereas object recognition is believed to rely on structures in the ventral (occipitotemporal) stream, object grasping appears to rely on structures in the dorsal (occipitoparietal) stream. We used functional magnetic resonance imaging (fMRI) to determine whether grasping (compared to reaching) produced activation in dorsal areas, ventral areas, or both. We found greater activity for grasping than reaching in several regions, including anterior intraparietal (AIP) cortex. We also performed a standard object perception localizer (comparing intact vs. scrambled 2D object images) in the same subjects to identify the lateral occipital complex (LOC), a ventral stream area believed to play a critical role in object recognition. Although LOC was activated by the objects presented on both grasping and reaching trials, there was no greater activity for grasping compared to reaching. These results suggest that dorsal areas, including AIP, but not ventral areas such as LOC, play a fundamental role in computing object properties during grasping.     

The effect of short-term changes in the body mass on anticipatory postural adjustments

The purpose of the study was to investigate whether anticipatory postural adjustments (APAs) are modified with short-term changes in the body mass. Nine subjects were asked to catch a 2.2 kg load with their arms extended under conditions of no weight and when additional weights of 10 and 20% of the subject’s body weight (BW) were attached to single body locations or when 20 or 40% BW were attached evenly to two locations. Attaching weights was associated with an increase of the whole body mass, but also involved changes in the vertical position of the center of mass (COM). Electromyographic activity of leg and trunk muscles and ground reaction forces were recorded and quantified within the typical time intervals of APAs. APAs were influenced by the magnitude of the weight attached to the body: an increase in the body mass was associated with anticipatory co-activation of trunk and leg muscles. The level of this co-activation increased with an increase in the magnitude of weight added to the body. At the same time, APAs were affected by the changes in the vertical position of COM. These findings suggest that in the case of short-term changes in the body mass, the CNS might prioritize information regarding the magnitude and location of the additional weight added to the body and utilize a strategy of anticipatory co-activation of postural muscles directed at the stabilization of body segments.     

身体姿势对腰椎小关节受力的影响

目的 :分析脊柱处于不同姿势时腰椎小关节受力大小及变化情况。方法 :采用 8具新鲜脊柱腰骶段 (L1～S1)标本 ,在MTS系统上用压敏片测量L4、5小关节面在中立位和前屈、后伸位时受力大小。结果 :中立位时L4、5小关节受力为 (3 1.16± 7.15 )N ,占轴向压缩载荷的 15 % ;前屈时小关节受力减小 ,前屈 10°、2 0°时受力大小为 (18.3 2± 4.46)N、(9.3 8± 1.82 )N ,占压缩载荷的比例减为 9%、5 % ;后伸时小关节受力增大 ,后伸 10°、2 0°时受力大小为 (4 5 .92± 11.0 6)N、(65 .68± 10 .16)N ,占压缩载荷的比例增至2 3 %、3 3 %。结论 :腰椎小关节在中立位能承受脊柱的一部分压缩载荷 ,且随脊柱姿势不同小关节面受力也不同。     

Effect of body posture on postexercise parasympathetic reactivation in men

The aim of the present study was to assess the influence of body posture on post-submaximal exercise parasympathetic reactivation and to examine whether this influence was preserved under a heightened sympathetic background. On four occasions, eleven moderately trained subjects (22.1 ± 3.0 years old) performed, in random order, two consecutive submaximal running bouts (CTs), each followed by 5 min passive recovery in an upright (Up), sitting (Sit), supine (Sup) or supine with legs up position (SupLu). Between both CTs, participants performed 150 s of supramaximal intermittent running (SI). Parasympathetic reactivation was assessed from heart rate recovery (HRR) and variability (HRV; e.g. rMSSD_{30 s}) indices calculated during the 5 min recovery periods [i.e. before (N) and after SI (post-SI)]. In the N condition, Sup position was associated with a faster and greater increase in rMSSD_{30 s} than Sit and SupLu (both P < 0.01), which were all higher compared with Up ( P < 0.001). A 'time' effect was shown in Sit, Sup and SupLu (all P < 0.05), but not in Up ( P = 0.99). All N values were higher than post-SI values ( P < 0.001), except for Up, where a trend was apparent ( P = 0.06). In the post-SI condition, a position effect was preserved for HRR ( P < 0.001), but not for HRV indices ( P = 0.99 for rMSSD_{30 s}). In conclusion, the supine position accelerated and increased parasympathetic reactivation more than the other three positions, but the posture effect was less evident following supramaximal exercise. In the context of an accentuated sympathetic background (i.e. post-SI), postexercise HRV indices are less gravity dependent than HRR, reflecting more the exercise-related changes in parasympathetic activity.     

Does body posture affect the parameters of a cutaneous electrogastrogram?

In a study aimed to test the effect of body position on the parameters derived from surface electrogastrograms, 17 healthy volunteers (2M, 15F; median age 22.5 years) attended in random order two examination sessions held on separate days. A 30-min recording of the interdigestive gastric myoelectrical activity (GMA) was followed by a 90-min postprandial recording after intake of a 394 kcal mixed solid-liquid test meal. For the first examination the subject was examined in a recumbent position, whereas for the second examination a sitting position was maintained. The dominant frequency and relative time occupied by normogastria was negligibly affected by the posture of the subject during GMA recording. However, a decrease in the dominant power (DP) of the gastric slow waves was observed during both the interdigestive and the postprandial recording period in a sitting position compared to a recumbent position. Consequently, the fed to fasted state DP ratio remained unaffected by body posture during GMA recording. The results indicate that by carefully observing procedural guidelines, good quality electrogastrograms can be obtained with a sitting subject, enabling the provision of comparable parameters to those achieved from standard examination in a recumbent position.     

Lateralized effects of hand and eye on anticipatory postural adjustments in visually guided aiming movements

This study investigated hemisphere-specific processing of visually aimed movements and associated postural adjustments while controlling for handedness and eyedness. Eleven right-handed, right-eyed and right-footed healthy adult volunteers performed, from a standing position, an aiming task under two hand (right and left hand) and three visual conditions (binocular vision, right and left eye monocular vision). Centre of pressure (CoP) displacement, hand kinematics and the target's position were synchronously recorded during performance of the aiming task. Analysis revealed a lower RMS error, a later postural adjustment onset and a smaller centre of pressure dispersion when aiming was performed with the dominant right compared to the non-dominant left hand. On the other hand, no differences on either aiming performance or postural adjustments were noted under the three visual conditions. These results suggest a strong handedness and absence of an eyedness effect on the accuracy of aiming and associated postural adjustments.     

Effect of posture on body temperature of young men in cold air

We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min⁻¹ whilst upright to 437 (SEM 42) ml·min⁻¹ whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m⁻² in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.     

Control of frontal plane body motion in human stepping

 During a step the body’s centre of mass (CoM) typically remains medial to the supporting foot and therefore the body is unstable and falling (sideways) under gravity. This may make it difficult to adjust the frontal-plane body motion appreciably once the step is under way. We have therefore investigated whether this motion could be controlled largely in a ballistic manner, that is by setting the initial (toe-off) position and velocity of the CoM such that the fall develops as required for the particular step without the need for appreciable mid-step adjustment. Subjects stepped in different directions and from different postures, and the resulting motion of their CoM in the frontal plane was compared with that of a single-segment mathematical model of the body which falls freely under the influence of gravity. The lateral position and velocity of subjects’ CoM at toe-off varied across the different step types in a manner consistent with a ballistic mode of control. Furthermore the model, given these positions and velocities as initial conditions, closely predicted the subsequent CoM motion. The results suggest that subjects may produce the different body trajectories required for different types of step largely in a ballistic manner. This would imply that the central nervous system must judge in advance the size and direction of the initial ”throw” given to the body-mass. Received: 12 August 1996 / Accepted: 18 December 1996     

Relative contribution of ankle and hip muscles in regulation of the human orthograde posture in a frontal plane

It was investigated, whether the postural regulation in the frontal plane takes place mainly at the hip or at the ankle level. The elimination of ankle torque was achieved by providing a point support in the frontal plane. (Two boards were attached to subject feet, below each board a metal pipe 2 cm diameter was fixed, so, the subject stood on contrivances resembling ‘skates’). The lateral displacements of breast and hip, the angle of ‘skates’ tilt and the characteristics of frontal stabilogram and electromyogram of two ankle muscles (m. peroneus and m. soleus) were compared in two situations: (1) during normal standing; (2) under the conditions of the exclusion of ankle torque from postural control. During normal standing the body behaved as two-link inverted pendulum. Transition from normal standing to standing on free ‘skates’ produced changes in the kinematics of body movement. Under the conditions of ankle torque exclusion (free ‘skates’) breast and hip of a subject moved in a frontal plane as a single unit (one-link inverted pendulum). During standing on free ‘skates’ the electromyographic activity of m. peroneus and m. soleus was the same as during normal standing (approximately 70–100 μV).