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Biomedical subjects

P DiZio

Publications and source records attributed to P DiZio.

At least 19 recordsLinked to original sources
PubMed1998

Auditory cues for orientation and postural control in sighted and congenitally blind people.

This study assessed whether stationary auditory information could affect body and head sway (as does visual and haptic information) in sighted and congenitally blind people. Two speakers, one placed adjacent to each ear, significantly stabilized center-of-foot-pressure sway in a tandem Romberg stance, while neither a single speaker in front of subjects nor a head-mounted sonar device reduced center-of-pressure sway. Center-of-pressure sway was reduced to the same level in the two-speaker condition for sighted and blind subjects. Both groups also evidenced reduced head sway in the two-speaker condition, although blind subjects' head sway was significantly larger than that of sighted subjects. The advantage of the two-speaker condition was probably attributable to the nature of distance compared with directional auditory information. The results rule out a deficit model of spatial hearing in blind people and are consistent with one version of a compensation model. Analysis of maximum cross-correlations between center-of-pressure and head sway, and associated time lags suggest that blind and sighted people may use different sensorimotor strategies to achieve stability.

Acoustic Stimulation↗
PubMed1996

Motor function in microgravity: movement in weightlessness.

Microgravity provides unique, though experimentally challenging, opportunities to study motor control. A traditional research focus has been the effects of linear acceleration on vestibular responses to angular acceleration. Evidence is accumulating that the high-frequency vestibulo-ocular reflex (VOR) is not affected by transitions from a 1 g linear force field to microgravity (<1 g); however, it appears that the three-dimensional organization of the VOR is dependent on gravitoinertial force levels. Some of the observed effects of microgravity on head and arm movement control appear to depend on the previously undetected inputs of cervical and brachial proprioception, which change almost immediately in response to alterations in background force levels. Recent studies of post-flight disturbances of posture and locomotion are revealing sensorimotor mechanisms that adjust over periods ranging from hours to weeks.

Animals↗
PubMed1993

Gravitoinertial force level influences arm movement control.

1. The ability to move the forearm between remembered elbow joint angles immediately after rapid increases or decreases of the background gravitoinertial force (G) level was measured. The movements had been well-practiced in a normal 1G environment before the measurements in high-(1.8G) and low-force (0G) environments. The forearm and upper arm were always unsupported to maximize the influence of altered G-loading and to minimize extraneous cues about arm position. 2. Horizontal and vertical movement planes were studied to measure the effects of varying the G load in the movement plane within a given G background. Rapid and slow movements were studied to assess the role of proprioceptive feedback. 3. G level did not affect the amplitude of rapid movements, indicating that subjects were able to plan and to generate appropriate motor commands for the new G loading of the arm. The amplitude of slow movements was affected by G level, indicating that proprioceptive feedback is influenced by G level. 4. The effects of G level were similar for horizontal and vertical movements, indicating that proprioceptive information from supporting structures, such as the shoulder joint and muscles, had a role in allowing generation of the appropriate motor commands. 5. The incidence and size of dynamic overshoots were greater in 0G and for rapid movements. This G-related change in damping suggests a decrease in muscle spindle activity in 0G. A decrease in muscle spindle activity in 0G and an increase in 1.8G are consistent with the results of our prior studies on the tonic vibration reflex, locomotion, and perception of head movement trajectory in varying force backgrounds.

Adult↗
PubMed1993

The role of brachial muscle spindle signals in assignment of visual direction.

1. In the oculobrachial illusion, a target light attached to the unseen stationary hand is perceived as moving and changing spatial position when illusory motion of the forearm is elicited by brachial muscle vibration. Our goal was to see whether we could induce apparent motion and displacement of two retinally fixed targets in opposite directions by the use of oculobrachial illusions. 2. We vibrated both biceps brachii, generating illusory movements of the two forearms in opposite directions, and measured any associated changes in perceived distance between target lights on the unseen stationary hands. The stability of visual fixation of one of the targets was also measured. 3. The seen distance between the stationary targets increased significantly when vibration induced an illusory increase in felt distance between the hands, both with binocular and monocular viewing. 4. Subjects maintained fixation accuracy equally well during vibration-induced illusory increases in visual target separation and in a no-vibration control condition. Fixation errors were not correlated with the extent or direction of illusory visual separation. 5. These findings indicate that brachial muscle spindle signals can contribute to an independent representation of felt target location in head-centric coordinates that can be interrelated with a visual representation of target location generated by retinal and oculomotor signals. 6. A model of how these representations are interrelated is proposed, and its relation to other intersensory interactions is discussed.

Arm↗
PubMed1993

Spatial stability, voluntary action and causal attribution during self-locomotion.

Adaptive changes in locomotory control and perception occur in environments where the normal relationship between effort and body displacement is altered (1,2). We have further investigated this plastic relationship by altering visual feedback during voluntary walking in place on a rotary treadmill. When the velocity of optical flow was increased or reversed relative to normal for the steps being made, subjects reported changes in perceived self-motion, the size, rate, and/or direction of their voluntary steps, the extent of voluntary effort required, and the apparent stability of a hand-held support bar. The floor and the visual environment were perceived as stable. We will show that these perceptual remappings obey "terrestrial constraints."

Adaptation, Physiological↗
PubMed1993

Multisensory, cognitive, and motor influences on human spatial orientation in weightlessness.

Exposure to weightlessness affects the control and appreciation of body position and orientation. In free fall the perception of one's own orientation and that of the surroundings is dependent on the presence or absence of contact cues, whether part of the body is visible in relation to the architecturally defined verticals of the space craft, cognitive factors, and exposure history. Sensations of falling are not elicited in free fall when the eyes are closed or the visual field is stabilized. This indicates that visual and cognitive factors as well as vestibular ones must be implicated in the genesis of such sensations under normal circumstances. Position sense of the limbs is also degraded in free fall. This may be due to alterations in skeletal muscle spindle gain owing to a decreased otolith-spinal activation. We provide evidence that during initial exposure to weightlessness there is a decrease in muscle stiffness which affects movement accuracy. The altered loading of the skeletal muscles due to the head and body being weightless are shown to be significant etiological factors in space motion sickness.

Cognition↗
PubMed1992

Gravitoinertial force level affects the appreciation of limb position during muscle vibration.

Illusory motion and displacement of the restrained forearm can be elicited by vibrating the biceps brachii or triceps brachii muscle. We measured the influence of gravitoinertial force level on these perceptual responses to vibration during parabolic flight maneuvers where normal (1G) and high force (1.8G) background levels alternated with microgravity (0G). Subjects indicated the apparent forearm position of the vibrated arm with the other forearm and also made verbal reports. Biceps brachii vibration induced illusory extension of the forearm and triceps brachii, illusory flexion; these apparent motions and displacements were highly G force-dependent being enhanced at 1.8G and diminished at 0G relative to normal 1G force level. These alterations are discussed in terms of vestibulo-spinal and propriospinal influences on alpha-gamma motoneuronal control of muscle tone and the varying requirements for postural load support in different force backgrounds. Their implications for the control and appreciation of limb movements during exposure to different G force levels are also described.

Arm↗
PubMed1991

Decreased susceptibility to motion sickness during exposure to visual inversion in microgravity.

Head and body movements made in microgravity tend to bring on symptoms of motion sickness. Such head movements, relative to comparable ones made on Earth, are accompanied by unusual combinations of semicircular canal and otolith activity owing to the unloading of the otoliths in OG. Head movements also bring on symptoms of motion sickness during exposure to visual inversion (or reversal) on Earth because the vestibulo-ocular reflex is rendered anti-compensatory. Here, we present evidence that susceptibility to motion sickness during exposure to visual inversion is decreased in a 0G relative to a 1G force background. This difference in susceptibility appears related to the alteration in otolith function in 0G. Some implications of this finding for the etiology of space motion sickness are described.

Adult↗
PubMed1991

Motion sickness susceptibility in parabolic flight and velocity storage activity.

In parabolic flight experiments, we have found post-rotary nystagmus to be differentially suppressed in free fall (OG) and in a high gravitoinertial force (1.8G) background relative to 1G. In addition, the influence of postrotary head movements on nystagmus suppression was found to be contingent on G level. The nature of this pattern indicated a G-dependency of the velocity storage and dumping mechanisms. Here, we have rank-correlated susceptibility to motion sickness during head movements in OG and 1.8G with the following: a) the decay time constant of the slow phase velocity of post-rotary nystagmus under 1G, no head movement, baseline conditions, b) the extent of time constant reduction elicited in OG and 1.8G; c) the extent of time constant reduction elicited by head tilts in 1G; and d) changes in the extent of time constant reduction in OG and 1.8G over repeated tests. Susceptibility was significantly correlated with the extent to which a head movement reduced the time constant in 1G, was weakly correlated with the baseline time constant, but was not correlated with the extent of reduction in OG or 1.8G. This pattern suggests a link between mechanisms evoking symptoms of space motion sickness and the mechanisms of velocity storage and dumping. Experimental means of evaluating this link are described.

Adolescent↗
PubMed1990

Sensory-motor factors triggering the suppression of post-rotary vestibular responses in different gravitoinertial force backgrounds.

We studied suppression of oculomotor and perceptual after-responses by post-rotary head movements in high (1.8 G), low (0 G), and normal (1 G) gravitoinertial force backgrounds in parabolic flight. Our aim was to identify what sensory and motor signals are critical for triggering suppression. In a prior experiment (DiZio and Lackner 1988), we found suppression using 40 degrees post-rotary head tilts in 1 G and 1.8 G but not 0 G force backgrounds. However, in free fall even without head tilts there was a significant suppression of nystagmus relative to 1 G and 1.8 G force backgrounds, thus potentially masking an effect of head tilt on suppression in 0 G. We have retested four of the original subjects with 90 degrees head tilts to maximize the likelihood of detecting suppression in 0 G. Although nystagmus and illusory after-rotation were suppressed by post-rotary head tilts in normal and high gravitoinertial force environments, there was still no evidence of suppression in free fall. We present evidence that the lack of suppression in 0 G is not attributable to post-rotary responses already being at a "basement" level, but rather that suppression depends on the registration of a change in head position relative to a significant level of gravitoinertial force.

Aerospace Medicine↗
PubMed1990

Age differences in oculomotor responses to step changes in body velocity and visual surround velocity.

We compared the slow-phase eye velocity elicited by sudden cessation of prolonged, constant velocity, vertical z-axis rotation of the body or the visual surround in 10 healthy college-age and over-65 individuals. The step gain of vestibular post-rotary nystagmus did not differ across age groups, but the time constant of slow-phase velocity decay was longer and more asymmetrical in the older group. The slow-phase velocity of optokinetic nystagmus attained the same initial levels for both age groups; it declined significantly during 60 s of stimulation for the older but not the younger group. The decay rate of optokinetic afternystagmus was quicker for the older subjects. This pattern of results may be related to already identified structural changes in the vestibular system and suggests the existence of yet unidentified changes in central vestibular and visual processing.

Adolescent↗
PubMed1989

Perceived self-motion elicited by postrotary head tilts in a varying gravitoinertial force background.

We measured the effects of postrotary head tilts on the perceived duration and the apparent axis of illusory self-rotation experienced following counterclockwise body rotation in high (1.8 G), normal (1 G), and low (0 G) gravitoinertial force environments. In the absence of head movements, the duration of illusory afterrotation was shorter in 0 G and 1.8 G than in 1 G, and it was further shortened by 40 degrees pitch-back head movements in 1 G and 1.8 G. Clockwise illusory afterrotation about the torso's vertical z-axis was always experienced in trials without postrotary head tilts. In trials with head movements, half the subjects experienced no change in this pattern; however, half experienced transient rightward roll of the torso's z-axis, which remained the rotation axis. The duration and extent of apparent roll were greater in 0 G and smaller in 1.8 G than in 1 G. We provide a functional explanation for the tendency for perceived self-rotation to be determined relative to the torso and to the gravitoinertial vertical rather than solely in relation to head position and head-fixed angular velocity sensors.

Adult↗
PubMed1989

Altered sensory-motor control of the head as an etiological factor in space-motion sickness.

Mechanical unloading during head movements in weightlessness may be an etiological factor in space-motion sickness. We simulated altered head loading on Earth without affecting vestibular stimulation by having subjects wear a weighted helmet. Eight subjects were exposed to constant velocity rotation about a vertical axis with direction reversals every 60 sec. for eight reversals with the head loaded and eight with the head unloaded. The severity of motion sickness elicited was significantly higher when the head was loaded. This suggests that altered sensory-motor control of the head is also an etiological factor in space-motion sickness.

Gravitation↗
PubMed1988

The effects of gravitoinertial force level and head movements on post-rotational nystagmus and illusory after-rotation.

The effect of Coriolis, cross-coupled stimulation on the vestibuloocular reflex and the elicitation of motion sickness depends on background gravitoinertial force level (DiZio et al. 1986, 1987; Graybiel et al. 1977; Lackner and Graybiel 1984, 1986). We have explored whether this response dependency is related to the unusual patterns of sensorimotor activity present during exposure to non-terrestrial gravitoinertial force levels, to alterations in the encoding of head movements in different gravitoinertial force environments, or to some combination thereof. Blindfolded subjects were exposed to sudden stops after constant velocity, vertical z-axis rotation, sometimes with and sometimes without post-rotational head movements, in the 0 G, 1 G, and 1.8 G force phases of parabolic flight. After sudden stops without head movements, the time constant of decay of post-rotational nystagmus was significantly lower in 0 G than in 1 G and lower to a smaller extent in 1.8 G. Post-rotational head movements decreased the decay time constants in 1 G and in 1.8 G, but not in free fall. The same pattern emerged for the duration of illusory after-rotation. Systematic changes were not found in the peak slow phase velocity of nystagmus. These results suggest that tonic levels of otolithic and somatosensory activity in combination with canalicular, cervical, and motor activity regulate the velocity storage mechanism of the horizontal vestibuloocular reflex (Cohen et al. 1977; Raphan et al. 1979) and sensations of after-rotation. These same factors are likely to be important etiological elements in space motion sickness.

Coriolis Force↗
PubMed1988

Visual stimulation affects the perception of voluntary leg movements during walking.

When a limb is used for locomotion, patterns of afferent and efferent activity related to its own motion are present as well as visual, vestibular, and other proprioceptive information about motion of the whole body. A study is reported in which it was asked whether visual stimulation present during whole-body motion can influence the perception of the leg movements propelling the body. Subjects were tested in conditions in which the stepping movements they made were identical but the amount of body displacement relative to inertial space and to the visual surround varied. These test conditions were created by getting the subjects to walk on a rotatable platform centered inside a large, independently rotatable, optokinetic drum. In each test condition, subjects, without looking at their legs, compared, against a standard condition in which the floor and drum were both stationary, their speed of body motion, their stride length and stepping rate, the direction of their steps, and the perceived force they exerted during stepping. When visual surround motion was incompatible with the motion normally associated with the stepping movements being made, changes in apparent body motion and in the awareness of the frequency, extent, and direction of the voluntary stepping movements resulted.

Adult↗
PubMed1987

The influence of gravitoinertial force level on oculomotor and perceptual responses to Coriolis, cross-coupling stimulation.

Susceptibility to motion sickness during exposure to constant levels of Coriolis, cross-coupling stimulation is lower in zero G and higher in 1.8 G than in a 1-G force environment (10, 13). The goal of the present experiment was to determine whether gravitoinertial force magnitude also influences oculomotor and perceptual responses to Coriolis, cross-coupling stimulation. We had blind-folded subjects who were rotating at constant velocity make standardized head movements during the free-fall and high force phases of parabolic flight, and we measured both the characteristics of their horizontal nystagmus and the magnitude of their experienced self-motion. Both responses were less intense in the free-fall periods than in the high force periods. Although the slow phase velocity of nystagmus reached the same initial, peak level in both conditions, it decayed more quickly in zero G. These findings suggest that the response to semicircular canal stimulation depends on the background level of gravitoinertial force.

Adult↗
PubMed1987

The influence of gravitoinertial force level on oculomotor and perceptual responses to sudden stop stimulation.

Our goal was to determine whether the vestibular response to vertical, z-axis body rotation in the dark is influenced by the magnitude of gravitoinertial force. We measured the nystagmus and the duration of illusory self-motion elicited in blindfolded subjects by cessation of such rotation during the free-fall, high, and terrestrial force phases of parabolic flight maneuvers. Both measures were significantly lower in zero G than in 1 G, and lower to a smaller extent in 1.8 G. The decreased intensity of nystagmus was due specifically to a decrease in the time constant of slow phase velocity decay with no decrement in peak velocity. This pattern of findings is consistent with the responses we had observed earlier to constant levels of Coriolis, cross-coupled stimulation during parabolic flight maneuvers both in terms of the mode of nystagmus suppression and the effect of G-level. Attenuation of the vestibular response to rotary acceleration in free-fall causes sensory-motor mismatches during natural head movements in orbital flight that may be important factors in the evocation of space motion sickness.

Coriolis Force↗