Interventions for premature infants.
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Body Weight↗
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Results for “Kinesthesis”
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Is the organisation of goal-directed action modality specific? A common temporal structure.
With the help of kinematic analysis, the temporal organization of the complex daily activity 'drinking from a bottle with a glass' was described in detail. The analysis focused on the sequential action structure, the prehensile acts, and the bimanual coordination as well as on the effect of different instruction modalities on these parameters to explore the underlying representation for this complex action. Movements of the two arms were recorded in three-dimensional space with the help of an optoelectronic device in 12 normal subjects under four conditions: (1) action pantomime after verbal instruction; (2) action imitation after observation of the action performed by the experimenter without the objects; (3) action pantomime while seeing, but not touching the objects; and finally (4) action execution with objects. Despite high execution variability, the temporal structure of the action could be precisely described by the relative duration and peak velocity of action segments, by the MGA-object size-correlation, and by linear regression analysis between the onsets of functionally related action segments. A similar structure of the action as characterized by these kinematic parameters was retained across different instruction modalities. Only when the action was executed with the objects, the interval between the movement onsets of either hand and the peak velocity of the manipulative acts were reduced, while no change was observed across the other three instruction modalities. This stability of the temporal structure suggests the existence of a level in the representation of an action where all the modalities converge.
Attention↗
Categorisation of 'perceptual' and 'premotor' neglect patients across different tasks: is there strong evidence for a dichotomy?
The aim of the presented studies was to investigate whether classifications of neglect patients into perceptual (i.e. identifying a patient as suffering from mainly attentional/space representation deficits) and premotor (judging the main impairment to be related towards actions into contralesional space) categories is consistent across different line bisection assessment techniques that have, in the past, been designed to tease these potentially overlapping aspects of hemispatial neglect apart. Twelve patients with hemispatial neglect and three control groups were tested with the Overhead Task, adapted from Nico [Neuropsychologia 34 (1996) 471] in which patients were asked to bisect lines that were mirror reversed, the Pulley Device Technique, adapted from Bisiach et al. [Neurology 40 (1990) 1278] in which they had to perform a movement opposite to the direction of the transaction mark that bisected the line and the Landmark Test, adapted from Milner et al. [Neuropsychologia 30 (1992) 515] in which they had to manually point to the half of a centrally pre-bisected line that, to them, appeared shorter. The specific question was whether these three tasks would categorise the same set of patients in the same way?Most patients could be classified into either the premotor or perceptual category in each task, but no consistent categorisation emerged across the three techniques. Just 1 out of the 12 patients, was consistently classified across all three tasks. It seemed that despite the fact that all tasks essentially required a line bisection response, the perceptual and motor differences between the tasks were still great enough to result in inconsistent classifications. The Landmark Task classified the majority of patients into the perceptual neglect category, while the Overhead and Pulley Device Techniques tended to identify more patients as suffering from a premotor deficit (albeit not the same set of patients).
Aged↗
Laterality effects on motor awareness.
The ability to perceive self-produced movements and to correctly attribute an action to its proper agent is a natural task and a basic requirement to human social communication. Recent experiments suggest that this apparently simple phenomenon is related to the mechanisms of motor production, raising the question whether recognition of self-produced movement is affected by asymmetries similar to those present in motor skills. In this study, right- and left-handed subjects decided whether a moving hand presented on a screen was the image of their own hand or of that of another person. Two experimental conditions were tested: either subjects saw their own moving hand (subject condition) or they were shown the experimenter's hand pantomiming their movement (experimenter condition); a glove masked morphological differences between the two hands. Verbal responses and response times were analysed. Results showed that all subjects were more accurate in recognising their preferred hand with respect to their non-preferred hand. Right-handers responded faster than left-handers did, the latter group being especially slowed down in the experimenter condition. On the contrary, in the right-handers group, response times did not differ among conditions. The present data indicate that the ability to recognise self-generated movements is affected by motor dominance, thus suggesting that conscious knowledge of self-produced movements is closely related to the motor system.
Adolescent↗
Cells in monkey STS responsive to articulated body motions and consequent static posture: a case of implied motion?
We show that populations of visually responsive cells in the anterior part of the superior temporal sulcus (STSa) of the macaque monkey code for the sight of both specific articulated body actions and the consequent articulated static body postures. We define articulated actions as actions where one body part (e.g. a limb or head) moves with respect to the remainder of the body which remains static; conversely non-articulated actions are actions where the equivalent body parts do not move with respect to each other but move as one. Similarly, articulated static body postures contain a torsion or rotation between parts, while non-articulated postures do not. Cells were tested with the sight of articulated and non-articulated actions followed by the resultant articulated or non-articulated static body postures. In addition, the static body postures that formed the start and end of the actions were tested in isolation. The cells studied did not respond to the sight of non-articulated static posture, which formed the starting-point of the action, but responded vigorously to the articulated static posture that formed the end-point of the action. Other static postures resembling the articulated end-point posture, but which were in a more relaxed muscular state (i.e. non-articulated), did not evoke responses. The cells did not respond to body actions that were less often associated with the effective static articulated postures. Our results suggest that the cells' responses were related to the implied action rather than the static posture per se. We propose that the neural representations in STSa for actual biological motion may also extend to biological motion implied from static postures. These representations could play a role in producing the activity in the medial temporal/medial superior temporal (V5(MT)/MST) areas reported in fMRI studies when subjects view still photographs of people in action.
Action Potentials↗
The effects of gender, menstrual phase and practice on the perceived location of the midsagittal plane.
Women show menstrual phase-related cognitive changes that suggest altered hemispheric activation for a particular task, such that they demonstrate the greatest lateral performance differences on prototypical left hemisphere tasks during the luteal phase and on prototypical right hemisphere tasks during menstruation. Additionally, menstrual phase may alter total cerebral responsiveness, such that response times and performance accuracy for many tasks are best during the luteal phase and most impaired during the menstrual phase. We evaluated the effect of menstrual phase on spatial bisection (a perceptuospatial task) to help further understand hormonally-mediated changes in interhemispheric dynamics. Healthy young adult women and men blindly pointed to their midsagittal plane with either hand. Women were repeatedly tested according to menstrual phase, and men were tested at similar intervals. The mean pointing error in the luteal phase differed significantly from that of all other phases and did not differ significantly from those of men, who pointed significantly to the left across test sessions. These findings suggest that, in space bisection tasks, women are more likely to have asymmetric hemispheric activation during the luteal phase than during the menstrual phase. Thus, space bisection did not resemble other prototypical right hemisphere behaviors. The luteal phase may have nonspecifically activated both hemispheres on this task instead of suppressing right hemisphere function, and a slight functional asymmetry favoring the right hemisphere may have been promoted. In addition, intermanual pointing discrepancies in both subject groups decreased over repeated sessions. This suggests that, while practice alters an internal kinesthetic reference, it does not influence an imaginal extrapersonal spatial reference.
Adolescent↗
Limited conscious monitoring of motor performance in normal subjects.
Normal subjects traced sagittal lines on a graphic tablet using a stylus held in their right hand. The hand was hidden by a mirror in which they saw the lines projected from a computer screen. In normal trials, the line seen in the mirror exactly corresponded to the traced line. In perturbed trials, a bias was introduced by the computer, so that the line appeared to deviate in one direction (right or left) by a variable angle (2, 5, 7 or 10 degrees). Subjects consistently displaced their hand in the opposite direction for producing a visually sagittal line. After each trial, they were asked in which direction they thought their hand had moved. In perturbed trials, they grossly underestimated the hand deviation. In addition, a post-hoc analysis revealed that one group of subjects misperceived the direction of their hand movement in the direction opposite to the perturbation (Group 1, including 9 Ss), whereas the other group gave responses in the correct direction (Group 2, including 4 Ss). In a second session using the same experimental paradigm, a motor response was asked for: subjects had to indicate the perceived direction of their hand during each trial by drawing a line with their eyes closed. Again, responses indicated a poor conscious monitoring of motor performance. These results suggest that normal subjects are not aware of signals generated by their own movements.
Adult↗
Imagined transformations of bodies: an fMRI investigation.
A number of spatial reasoning problems can be solved by performing an imagined transformation of one's egocentric perspective. A series of experiments were carried out to characterize this process behaviorally and in terms of its brain basis, using functional magnetic resonance imaging (tMRI). In a task contrast designed to isolate egocentric perspective transformations, participants were slower to make left-right judgments about a human figure from the figure's perspective than from their own. This transformation led to increased cortical activity around the left parietal-temporal-occipital junction, as well as in other areas including left frontal cortex. In a second task contrast comparing judgments about inverted figures to judgments about upright figures (always from the figure's perspective), participants were slower to make left-right judgments about inverted figures than upright ones. This transformation led to activation in posterior areas near those active in the first experiment, but weaker in the left hemisphere and stronger in the right, and also to substantial left frontal activation. Together, the data support the specialization of areas near the parietal-temporal-occipital junction for egocentric perspective transformations. These results are also suggestive of a dissociation between egocentric perspective transformations and object-based spatial transformations such as mental rotation.
Adult↗
Guide lines to deep structures and dynamics of intrinsic muscles of the hand.
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Anatomy, Regional↗
Heading and path percepts from visual flow and eye pursuit signals.
The percept of self-motion through the environment is supported by visual motion signals and eye movement signals. The interaction between these signals by decoupling of the eye movement and the pattern of retinal motion during brief simulated ego-movement on straight or circular trajectories was studied. A new response method enabled subjects to report perceived destination and perceived curvature of their future path simultaneously. Various combinations of simulated gaze rotation in the retinal flow and eye pursuit were investigated. Simulated gaze rotation ranged from consistent and larger than, to opponent and larger than eye pursuit. It was found that the perceived destination shifts non-linearly with the mismatch between simulated gaze rotation and eye pursuit. The non-linearity is also revealed in the perceived tangent heading direction and perceived path curvature, although to different extent in different subjects. For the same retinal flow, eye pursuit that is consistent with the simulated gaze rotation reduces heading error and the perceived path straightens out. In contrast, perceived path and/or heading do not become more curved or more biased in the direction opposite to pursuit when the eye -in-head rotation is opposite to the simulated gaze rotation. These observations point to modulation of the effect of the extra-retinal pursuit signal by the visual evidence for eye rotation. In a second experiment, one presented to a stationary eye the sum of a component of simulated gaze rotation and radial flow. It was found that the bi-circular flow component, that characterizes the change in pattern of flow directions by the gaze rotation, induces a shift of perceived heading without appreciable perceived path curvature. Conversely, the complementary component of simulated gaze rotation (bi-radial flow) evokes a percept of motion on a curved path with a small tangent heading error. It was suggested that bi-circular and bi-radial flow components contribute primarily to percepts of heading and path curvature, respectively.
Humans↗
Orienting otolith-ocular reflexes in the rabbit during static and dynamic tilts and off-vertical axis rotation.
Orienting otolith-ocular reflexes were assessed in rabbits using static tilt, off-vertical axis rotation (OVAR) and sinusoidal oscillation about earth-horizontal axes. In all paradigms, head pitch produced ocular counter-pitch and vergence, and head roll produced ocular counter-roll and conjugate yaw version. Thus, vergence and version are essential components of orienting reflexes along the naso-occipital and bitemporal axes. Vergence and version caused misalignment between the axes of eye and head movement during pitch and roll head movements. Semicircular canal input broadened the band-pass of these orienting reflexes, which would make them more appropriate when compensating for head movement during active motion.
Analysis of Variance↗
The subjective vertical and the sense of self orientation during active body tilt.
Previous testing of the ability to set a luminous line to the direction of gravity in passively-tilted subjects, in darkness, has revealed a remarkable pattern of systematic errors at tilts beyond 60 degrees, as if body tilt is undercompensated or underestimated (Aubert or A-effect). We investigated whether these consistent deviations from orientation constancy can be avoided during active body tilt, where more potential cues about body tilt (e.g. proprioception and efference copy) are available. The effects of active body tilt on the subjective vertical and on the perception of self tilt were studied in six subjects. After adopting a laterally-tilted posture, while standing in a dark room, they indicated the subjective vertical by adjusting a visual line and gave their verbal estimate of head orientation, expressed on a clock scale. Head roll tilts covered the range from -150 degrees to +150 degrees. The subjective vertical results showed no sign of improvement. Actively-tilted subjects still exhibited the same pattern of systematic errors that characterised their performance during passive tilt. Random errors in this task showed a steep monotonic increase with tilt angle, as in earlier passive tilt experiments. By contrast, verbal head-tilt estimates in the active experiments showed a clear improvement and were now almost devoid of systematic errors, but the noise level remained high. Various models are discussed in an attempt to clarify how these task-related differences and the selective improvement of the self-tilt estimates in the active experiments may have come about.
Adult↗
Neural model for processing the influence of visual orientation on visually perceived eye level (VPEL).
An individual line or a combination of lines viewed in darkness has a large influence on the elevation to which an observer sets a target so that it is perceived to lie at eye level (VPEL). These influences are systematically related to the orientation of pitched-from-vertical lines on pitched plane(s) and to the lengths of the lines, as well as to the orientations of lines of 'equivalent pitch' that lie on frontoparallel planes. A three-stage model processes the visual influence: The first stage parallel processes the orientations of the lines utilizing 2 classes of orientation-sensitive neural units in each hemisphere, with the two classes sensitive to opposing ranges of orientations; the signal delivered by each class is of opposite sign in the two hemispheres. The second stage generates the total visual influence from the parallel combination of inputs delivered by the 4 groups of the first stage, and a third stage combines the total visual influence from the second stage with signals from the body-referenced mechanism that contains information about the position and orientation of the eyes, head, and body. The circuit equation describing the combined influence of n separate inputs from stage 1 on the output of the stage 2 integrating neuron is derived for n stimulus lines which possess any combination of orientations and lengths; Each of the n lines is assumed to stimulate one of the groups of orientation-sensitive units in visual cortex (stage 1) whose signals converge on to a dendrite of the integrating neuron (stage 2), and to produce changes in postsynaptic membrane conductance (g(i)) and potential (V(i)) there. The net current from the n dendrites results in a voltage change (V(A)) at the initial segment of the axon of the integrating neuron. Nerve impulse frequency proportional to this voltage change signals the total visual influence on perceived elevation of the visual field. The circuit equation corresponding to the total visual influence for n equal length inducing lines is V(A)= sum V(i)/[n+(g(A)/g(S))], where the potential change due to line i, V(i), is proportional to line orientation, g(A) is the conductance at the axon's summing point, and g(S)=g(i) for each i for the equal length case; the net conductance change due to a line is proportional to the line's length. The circuit equation is interpreted as a basis for quantitative predictions from the model that can be compared to psychophysical measurements of the elevation of VPEL. The interpretation provides the predicted relation for the visual influence on VPEL, V, by n inducing lines each with length l: thus, V=a+[k(i) sum theta(i)/n+(k(2)/l)], where theta(i) is the orientation of line i, a is the effect of the body-referenced mechanism, and k(1) and k(2) are constants. The model's output is fitted to the results of five sets of experiments in which the elevation of VPEL measured with a small target in the median plane is systematically influenced by distantly located 1-line or 2-line inducing stimuli varying in orientation and length and viewed in otherwise total darkness with gaze restricted to the median plane; each line is located at either 25 degrees eccentricity to the left or right of the median plane. The model predicts the negatively accelerated growth of VPEL with line length for each orientation and the change of slope constant of the linear combination rule among lines from 1.00 (linear summation; short lines) to 0.61 (near-averaging; long lines). Fits to the data are obtained over a range of orientations from -30 degrees to +30 degrees of pitch for 1-line visual fields from lengths of 3 degrees to 64 degrees, for parallel 2-line visual fields over the same range of lengths and orientations, for short and long 2-line combinations in which each of the two members may have any orientation (parallel or nonparallel pairs), and for the well-illuminated and fully structured pitchroom. In addition, similar experiments with 2-line stimuli of equivalent pitch in the frontoparallel plane were also fitted to the model. The model accounts for more than 98% of the variance of the results in each case.
Humans↗
Influences of visual pitch and visual yaw on visually perceived eye level (VPEL) and straight ahead (VPSA) for erect and rolled-to-horizontal observers.
Localization within the space in front of an observer can be specified along two orthogonal physical dimensions: elevation ('up', 'down') and horizontal ('left','right'). For the erect observer, these correspond to egocentric dimensions along the long and short axes of the body, respectively. However, when subjects are rolled-to-horizontal (lying on their sides), the correspondence between the physical and egocentric dimensions is reversed. Employing egocentric coordinates, localization can be referred to a central perceptual point-visually perceived eye level (VPEL) along the long axis of the body, and visually perceived straight ahead (VPSA) along the short axis of the body. In the present experiment, measurements of VPEL and of VPSA were made on each of eight subjects who were either erect or rolled-to-horizontal while monocularly viewing a long 2-line stimulus (two parallel, 64 degrees -long lines separated by 50 degrees ) in otherwise complete darkness that was centered on the eye of the observer and was tilted out of the frontoparallel plane by a variable amount and direction (from -30 degrees to +30 degrees in 10 degrees steps). The stimulus tilt was either around an axis through the center of the two eyes (pitch; VPEL was measured) or around the long axis of the body that passed through the center of the viewing eye (yaw; VPSA was measured). Large variations in the localization settings were measured that were systematic with stimulus tilt. The slopes of the functions plouing the deviations from veridicality against the orientation of the 2-line stimulus ('induction functions') were larger for the rolled-to-horizontal observer than for the erect observer for both VPEL and VPSA, and for a given body orientation were larger for the VPEL discrimination than for the VPSA discrimination; the influences of body orientation in physical space and the direction of the discrimination relative to the body were lineraly additive. Both the y-intercepts of the induction functions and the central perceptual point measured in complete darkness were lower when the norm setting by the subject was along the vertical than when it was along the horizontal; this held for both the VPEL and VPSA discriminations. The systematic effects of body orientation on the slopes and of line orientation on the y-intercepts and dark values result from an effect of gravity on the settings and fit well to a general principle: any departure from erect posture increases the induction effects of the visual stimulus. The effect of gravity is consistent with the effect of gravity in previous work in high-g environments with the VPEL discrimination.
Analysis of Variance↗
The stationarity hypothesis: an allocentric criterion in visual perception.
Having long considered that extraretinal information plays little or no role in spatial vision, the study of structure from motion (SfM) has confounded a moving observer perceiving a stationary object with a non-moving observer perceiving a rigid object undergoing equal and opposite motion. However, recently it has been shown that extraretinal information does play an important role in the extraction of structure from motion by enhancing motion cues for objects that are stationary in an allocentric, world-fixed reference frame (Nature 409 (2001) 85). Here, we test whether stationarity per se is a criterion in SfM by pitting it against rigidity. We have created stimuli that, for a moving observer, offer two interpretations: one that is rigid but non-stationary, another that is more stationary or less rigid. In two experiments, with subjects reporting either structure or motion, we show that stationary, non-rigid solutions are preferred over rigid, non-stationary solutions; and that when no perfectly stationary solutions is available, the visual system prefers the solution that is most stationary. These results demonstrate that allocentric criteria, derived from extra-retinal information, participate in reconstructing the visual scene.
Adult↗
Geometrical properties of three-dimensional binocular eye position in light sleep.
We examined three-dimensional binocular positions in the alert and sleepy monkeys. In contrast to the tightly yoked eye movements observed in alertness, the eyes were usually converged, vertically misaligned and had a much larger torsional variability during light sleep. While in alertness eye position vectors were confined to fronto-parallel planes, the corresponding planes were rotated temporally (e.g. leftward for the left eye) in light sleep. There was no correlation between temporal rotation of the eye position planes and horizontal vergence. All these observations can be explained by randomly innervated extraocular muscles that are rotating the two eyes about anatomically determined axes.
Analysis of Variance↗
Absolute distance perception during in-depth head movement: calibrating optic flow with extra-retinal information.
We investigated the ability of monocular human observer to scale absolute distance during sagittal head motion in the presence of pure optic flow information. Subjects were presented at eye-level computer-generated spheres (covered with randomly distributed dots) placed at several distances. We compared the condition of self-motion (SM) versus object-motion (OM) using equivalent optic flow field. When the amplitude of head movement was relatively constant, subjects estimated absolute distance rather accurately in both the SM and OM conditions. However, when the amplitude changed on a trial-to-trial basis, subjects' performance deteriorated only in the OM condition. We found that distance judgment in OM condition correlated strongly with optic flow divergence, and that non-visual cues served as important factors for scaling distances in SM condition. Absolute distance also seemed to be better scaled with sagittal head movement when compared with lateral head translation.
Adolescent↗
Centric-minded templates for self-motion perception.
We propose a two-layer neuromorphic architecture by which motion field pattern, generated during locomotion, are processed by template detectors specialized for gaze-directed self-motion (expansion and rotation). The templates provide a gaze-centered computation for analyzing motion field in terms of how it is related to the fixation point (i.e., the fovea). The analysis is performed by relating the vectorial components of the act of motion to variations (i.e., asymmetries) of the local structure of the motion field. Notwithstanding their limited extension in space, such centric-minded templates extract, as a whole, global information from the input flow field, being sensitive to different local instances of the same global property of the vector field with respect to the fixation point; a quantitative analysis, in terms of vectorial operators, evidences this property as tuning curves for heading direction. Model performances, evaluated in several situations characterized by conditions of absence and presence of pursuit eye movements, validate the approach. We observe that the gaze-centered model provides an explicit testable hypothesis that can guide further explorations of visual motion processing in extrastriate cortical areas.
Computational Biology↗