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At least 793 records · Page 44Linked to original sources

PubMed1992

Biological movements look uniform: evidence of motor-perceptual interactions.

Six experiments demonstrate a visual dynamic illusion. Previous work has shown that in 2-dimensional (2D) drawing movements, tangential velocity and radius of curvature covary in a constrained manner. The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. The illusion is conspicuous: The variations of velocity in the stimuli exceed 200%. Yet movements are perceived as uniform. Conversely, 2D stimuli moving at constant velocity are perceived as strongly nonuniform. The illusion is robust: Exposure to true constant velocity fails to suppress it. Results cannot be explained entirely by the kinetic depth effect. The illusion is evidence of a coupling between motor and perceptual processes: Even in the absence of any intention to perform a movement, certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus.

Acceleration↗

PubMed1992

The role of balance dynamics in the active perception of orientation.

The Stoffregen and Riccio (1988) hypothesis that perceived orientation is determined primarily by balance dynamics was tested. Perception of orientation was evaluated in the context of a task that required Ss to control the roll orientation of a device in which they were seated. The device's direction of balance was manipulated across trials and thus was independent of gravity. Eighteen Ss participated in the investigation. After each trial, Ss estimated their mean tilt with respect to upright. Correlations of perceived tilt with tilt from balance were consistently higher than the correlations with gravity tilt. The dominance of balance over gravity depended on the magnitude of tilt from balance.

Adult↗

PubMed1992

Symmetry breaking dynamics of human multilimb coordination.

The dynamics of pattern formation and change are studied in a complex multicomponent system, specifically the arms and legs of human Ss. Among the novel features observed are differential stability of coordinative modes produced by limbs moving in the same versus different directions (Experiment 1); transitions between coordinative modes preceded by a slow drift in relative phase (Experiments 1 and 2); bifurcations or phase transitions from 1 four-limb pattern to another (Experiment 2); and spontaneous emergence of non-1:1-frequency- and phase-locked patterns, in addition to periods of relative coordination (Experiment 3). All observed relative phasing patterns and their dynamics (stability, loss of stability, intermittency) are shown to arise from the same underlying nonlinear dynamical structure, an important feature of which is broken symmetry.

Acceleration↗

PubMed1992

Role of the inertia tensor in perceiving object orientation by dynamic touch.

Ss wielded an occluded L-shaped rod and attempted to perceive the direction in which the rod was pointing with respect to the hand. The pattern of the rod's different resistances to rotation in different directions, quantified by the inertia tensor, changes systematically with the rod's orientation. Perception of orientation by wielding is possible if the tissue deformation consequences of the rod's inertia tensor are detectable. It was shown that perceived orientation was a linear function of actual orientation for both free and restricted wielding and for rods of different-size branches. The eigenvectors of the inertia tensor were implicated as the basis for this haptic perceptual capability. Results were discussed in reference to information-perception specificity and its implications for effortful or dynamic touch.

Adult↗

PubMed1992

How do somersaulters land on their feet?

Body movements of trampolinists landing upright from forward somersaults, with eyes open and closed, were analyzed to test a theory of how braking and timing of actions are conjointly controlled. In regulating landing, rotation has to be slowed by extending the body so that it reaches the upright just as the feet hit the trampoline. Extending a theory of visual control of linear braking, it was hypothesized that upright landing is achieved by perceptually regulating body extension so as to keep the ratio angle of body to upright: rate of change of angle (the tau function of the angle) proportional to time-to-landing. The data support the hypothesis, indicate that vision improves precision of control, and argue further for the value of the tau function in the perceptual regulation of action.

Attention↗

PubMed1993

Coupling dynamics in interlimb coordination.

In 1:1 frequency locking, the interlimb phase difference phi is an order parameter quantifying the spatial-temporal organization of 2 rhythmic subsystems. Dynamical modeling and experimental analyses indicate that an intentional parameter phi psi (intended coordination mode, phi = 0 degrees or phi = 180 degrees) and 2 control parameters omega c (coupled frequency) and delta omega (difference between uncoupled eigen-frequencies) affect phi. An experiment was conducted on 1:1 frequency locking in which phi psi, omega c, and delta omega were manipulated using a paradigm in which a person swings hand-held pendulums. As delta omega deviated from 0, the observed phi deviated from the phi psi, indicating a displacement in the phi attractor point. The displacements were exaggerated by increasing omega c. The displacements were coordinated with a decrease in the stability of phi and with higher harmonics in power spectrum of phi. Implications of the results for modeling interlimb coordination are discussed.

Adult↗

PubMed1993

Perceiving scene layout through an aperture during visually simulated self-motion.

This study tested scene perception during depicted self-movement. In Experiment 1, viewers reproduced angular scene configurations, revealed over time by camera motions in depth. Viewers used visible flow to update off-screen locations of landmarks that had been drawn from view and thereby perceived scenes in depth beyond the display's boundaries. Experiments 2 and 3 tested whether offscreen space is perceived as a function of depicted velocity and time and whether information from prior views is used. Viewers predicted when lateral movement would reveal a peripheral landmark whose location was shown in a prior panoramic view. Accurate responses, observed under certain conditions, would result if viewers perceived space according to S = integral of V dt (D. Algom & L. Cohen-Raz, 1984, 1987; R. Jagacinski, W. Johnson, & R. Miller, 1983). When required to picture wide spans in space yet to emerge, however, viewers responded as if these spans were compressed. The theoretical implications of the ability to retrieve, transform, and apply information after a discontinuous transition from a prior view are discussed.

Adult↗

PubMed1994

Grip-load force coupling: a general control strategy for transporting objects.

The authors examined the coupling of grip force and load force during point-to-point and cyclic arm movements while holding an object in a variety of grips, including 1- and 2-handed grips and "inverted" grips. In all grips, grip force is modulated in phase with fluctuations in load force that are induced by the arm movement. The tight temporal coupling between grip force and load force seen when moving an object held in a precision grip (J. R. Flanagan, J. Tresilian, & A. M. Wing, 1993) is observed in other grips. The control of precision grip force during whole-body jumping movements was also investigated. Grip force was modulated in phase with changes in load force induced by jumping even though the arm's joint angles were fixed. The tight temporal coupling between grip force and load force during object transport reflects a general control strategy that is not specific to any particular grip or mode of transport. Models of the coordination of grasp and transport in prehensile behaviors are discussed.

Acceleration↗

PubMed1995

Minimum-jerk, two-thirds power law, and isochrony: converging approaches to movement planning.

Two approaches to the study of movement planning were contrasted. Data on the drawing of complex two-dimensional trajectories were used to test whether the covariations of the kinematic and geometrical parameters of the movement formalized by the two-thirds power law and by the isochrony principle (P. Viviani & R. Schneider, 1991) can be derived from the minimum-jerk model hypothesis (T. Flash & N. Hogan, 1985). The convergence of the 2 approaches was satisfactory insofar as the relation between tangential velocity and curvature is concerned (two-thirds power law). Global isochrony could not be deduced from the optimal control hypothesis. Scaling of velocity within movement subunits can instead be derived from the minimum-jerk hypothesis. The implications vis-à-vis the issue of movement planning are discussed with an emphasis on the representation used by the motor control system for coding the intended trajectories.

Attention↗

PubMed1995

Calibration of human locomotion and models of perceptual-motor organization.

People coordinate the force and direction of skilled actions with target locations and adjust the calibrations to compensate for changing circumstances. Are the adjustments globally organized (adjusting a particular action to fit a particular circumstance would generalize to all actions in the same circumstance); anatomically specific (every effector is adjusted independently of others); of functional (adjustments would generalize to all actions serving the same goal and generating the same perceptible consequences)? Across 10 experiments, changes in the calibration of walking, throwing, and turning-in-place were induced, and generalization of changes in calibration to functionally related and unrelated actions were tested. The experiments demonstrate that humans rapidly adjust the calibration of their walking, turning, and throwing to changing circumstances, and a functional model of perceptual-motor organization is suggested.

Adult↗

PubMed1995

The inertia tensor as a basis for the perception of limb orientation.

The ability of humans to perceive the spatial orientation of an occluded arm was investigated. It was hypothesized that this ability is tied to the arm's inertial eigenvectors, invariant mechanical parameters corresponding to a limb's axes of rotational symmetry. By breaking the coincidence between the eigenvectors of the arm and its longitudinal axis, 3 experiments were directed at the possibility that the perceived orientation of an occluded arm would vary as a function of the eigenvectors. Overall, the angles in which the arm was positioned were affected by the direction in which the eigenvectors of the limb were oriented by small appended masses. Discussion focused on the importance of physical invariants for proprioception.

Adult↗

PubMed1995

Internal representations of the motor apparatus: implications from generalization in visuomotor learning.

Recent computational studies have proposed that the motor system acquires internal models of kinematic transformations, dynamic transformations, or both by learning. Computationally, internal models can be characterized by 2 extreme representations: structured and tabular (C. G. Atkeson, 1989). Tabular models do not need prior knowledge about the structure of the motor apparatus, but they lack the capability to generalize learned movements. Structured models, on the other hand, can generalize learned movements, but they require an analytical description of the motor apparatus. In investigating humans' capacity to generalize kinematic transformations, we examined which type of representation humans' motor system might use. Results suggest that internal representations are nonstructured and nontabular. Findings may be due to a neural network model with a medium number of neurons and synapses.

Adult↗

PubMed1995

Wayfinding, displacements, and mental maps: velocity fields are not typically used to determine one's aimpoint.

When an individual moves through a cluttered environment, he or she often fixates an object relatively near his or her path in the middle distance and uses pursuit eye movements to follow it while moving forward. On the basis of previous evidence, either motion fields or displacement fields around the fixated object--two alternative representations of the same information--could be used to determine one's direction of self-movement, sometimes called heading or aimpoint. In a series of 5 experiments, the relationship between these representations was explored and it was found that the displacements of identifiable objects, not their motions, are most likely the direct inputs for wayfinding. It may be that these inputs are used in conjunction with a mental map to determine one's aimpoint. A mathematical framework for this process is proposed.

Acceleration↗

PubMed1996

Adaptive spatial alignment and strategic perceptual-motor control.

When starting limb and target locations were simultaneously visible in a visuomotor task, performance during prism exposure was nearly perfect, but aftereffects were absent. When starting limb location was not visible, accurate exposure performance was slow to develop, but aftereffects were substantial. Adaptive spatial alignment of sensorimotor spaces and strategic perceptual-motor control to coordinate sensorimotor systems are distinct processes. However, realignment is dependent on whether the exposure task evokes control strategies that enable detection of misalignment. If the task can be performed solely by coding the visible difference between limb and target locations, misalignment detection is disabled. If movement is initiated by target location and then the limb is controlled by the visible difference between target and limb, the discordance between initialized and terminal locations enables misalignment detection and realignment.

Adult↗

PubMed1996

Grasping a fruit: selection for action.

This study used a natural task, with no emphasis placed on speeded responses, to investigate unconscious information processing. Using the ELITE system, a kinematic analysis was performed of the upper limb reach-to-grasp movement. Nine experiments explored how the presence of distractors affects the transport and grasp component of this movement. Experiment 1 showed that the kinematics for grasping apples, mandarins, cherries, and bananas were measurably different. Experiments 2A-D, 3, and 4 showed that these kinematics were not affected by the presence of nearby distractor fruits of either the same or a different kind. In Experiment 5, interference effects became evident when participants were required to perform a subsidiary task involving the distractor (counting the number of times a laterally placed fruit was illuminated). Experiment 6, requiring both grasping a target fruit and counting the number of times that this fruit was illuminated, revealed no interference effects. Taken together, these results suggest that selection for action does not involve substantial passive processing of distractors. However, dual-action processing of simultaneously presented objects does appear to involve automatic processing of even the task-irrelevant properties of the distractor.

Adolescent↗

PubMed1996

Visual control of posture during walking: functional specificity.

Three experiments examined the functional specificity of visually controlled posture during locomotion by presenting large-screen displays to participants walking on a treadmill. Displays simulated locomotion down a stationary hallway, a hallway that traveled with the observer, or a frontal wall that traveled with the observer. A superimposed oscillation specified postural sway in 6 possible directions. With the wall, sway amplitude was isotropic and directionally specific in all conditions. However, with the hallways, sway was anisotropic (lateral > anterior-posterior [AP]), and diagonal responses were flattened into the lateral plane. When the treadmill was turned 90 degrees to the hallway, both the anisotropy and flattening were reversed (AP > lateral), indicating that they are determined by the visual structure of the scene. The results can be explained by postural control laws based on both optical expansion and motion parallax, yielding biases in planar environments that truncate parallax.

Adult↗

PubMed1996

The relevance of action in perceiving affordances: perception of catchableness of fly balls.

The catchableness of a fly ball depends on whether the catcher can get to the ball in time; accurate judgments of catchableness must reflect both spatial and temporal aspects. Two experiments examined the perception of catchableness under conditions of restricted information pickup. Experiment 1 compared perceptual judgments with actual catching and revealed that stationary observers are poor perceivers of catchableness, as would be expected by the lack of information about running capabilities. In Experiment 2, participants saw the 1st part of ball trajectories before their vision was occluded. In 1 condition, they started to run (as if to catch the ball) before occlusion; in another, they remained stationary. Moving judgments were better than stationary judgments. This supports the idea that perceiving affordances that depend on kinematic, rather than merely geometric, body characteristics may require the relevant action to be performed.

Adult↗

PubMed1997

Perceiving and tracking kinesthetic stimuli: further evidence of motor-perceptual interactions.

Two experiments pursued previous studies (P. Viviani & P. Mounoud, 1990; P. Viviani & N. Stucchi, 1989) on motor-perceptual interactions. The right arm of blindfolded participants was moved passively along elliptic trajectories. Kinematics was either coherent or at variance with the relation (two-thirds power law) observed in active movements. In Experiment 1 participants compared the horizontal and vertical extent of the ellipses. Kinematics affected aspect ratio discrimination: The direction along which the movement decelerated was subjectively stretched. In Experiment 2 participants used the left arm to reproduce in real time the movement of the right arm. The trajectories of the left arm presented a stretch similar to the perceptual illusion demonstrated in Experiment 1. Between-arm asynchrony suggests that the motor control system cannot use kinesthetic information that is at variance with the flow of reafferences normally associated with voluntary movements. It is argued that these interactions occur at the level of a central amodal representation of the stimuli.

Arm↗