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Postural dynamics and the preferred critical boundary for visually guided reaching.

How do people choose an action to satisfy a goal from among the actions that are afforded by the environment? In 3 experiments the action modes used by actors to reach for a block placed at various distances from them were observed. In each experiment, when actors were not restricted in how they could reach for the object, the transition from their reaching using only arm extension to a mode of reaching in which they used the upper torso to lean forward occurred at closer distances than each actor's absolute critical boundary, beyond which the former action was no longer afforded. In Experiments 2 and 3 actors' seated posture was varied so that the effect of postural dynamics on the distance at which actors actually chose to make the transition between action modes, the preferred critical boundary, could be examined. The results are consistent with the proposal that the preferred critical boundary reflects the relative comfort of available modes of reaching.

Adult↗

Coordination dynamics of learning and transfer: collective and component levels.

The dynamics of learning a new coordinated behavior was examined by requiring participants to perform a visually specified phase relationship between the hands. Results showed that learning may involve qualitative or quantitative alterations in the layout of the coordination dynamics depending on whether such dynamics are bistable or multistable before exposure to the learning task. In both cases, the process stabilized the to-be-learned behavior and its symmetry partner, even though the latter had not actually been practiced. Kinematic analyses of hand motion showed that previously existing coordination tendencies were exploited during learning in order to match visual requirements. These findings and the concepts presented here provide a framework for understanding how learning occurs in the context of previous experience and allow individual differences in learning to be tackled explicitly.

Adult↗

Frames of reference and control parameters in visuomanual pointing.

Three hypotheses concerning the control variables in visuomanual pointing were tested. Participants pointed to a visual target presented briefly in total darkness on the horizontal plane. The starting position of the hand alternated randomly among 4 points arranged as a diamond. Results show that during the experiment, movement drifted from hypometric to hypermetric. Final positions depended on the starting position. Their average pattern reproduced the diamond of the starting points, either in same orientation (hypometric trials), or with a double inversion (hypermetric trials). The distribution of variable errors was elliptical, with the major axis aligned with the direction of the movement. Statistical analysis and Monte Carlo simulations showed that the results are incompatible with the final point control hypothesis (A. Polit & E. Bizzi, 1979). Better, but not fully satisfactory, agreement was found with the view that pointing involves comparing initial and desired postures (J. F. Soechting & M. Flanders, 1989a). The hypothesis that accounted best for the results is that final hand position is coded as a vector represented in an extrinsic frame of reference centered on the hand.

Adult↗

Functional stabilization of unstable fixed points: human pole balancing using time-to-balance information.

Humans are often faced with tasks that require stabilizing inherently unstable situations. The authors explored the dynamics of human functional stabilization by having participants continually balance a pole until a minimum time criterion was reached. Conditions were manipulated with respect to geometry, mass, and characteristic "fall time" of the pole. Distributions of timing between pole and hand velocities showed strong action-perception coupling. When actions demonstrated a potential for catastrophic failure, the period of hand oscillation correlated well with the perceptual quantity "time to balance" (tau(bal) = theta/theta), but not other quantities such as theta and theta alone. This suggests that participants were using available tau(bal) information during critical conditions, although they may not have been attending to this type of perceptual information during typical, noncritical motions of successful performance. In a model analysis and simulation, the authors showed how discrete tau(bal) information may be used to adjust the parameters of a controller to perform this task.

Adolescent↗

Perceiving motion while moving: how pairwise nominal invariants make optical flow cohere.

Computer-generated sequences simulated observer movement toward 10 randomly placed poles, 1 moving and 9 stationary. When observers judged their direction of movement, or heading, they used 3 related invariants: The (a) convergence and (b) decelerating divergence of any 2 poles specified that heading was to the outside of the nearer pole, and the (c) crossover of 2 poles specified that heading was to the outside of the farther pole. With all poles stationary, the field of 45 pairwise movements yielded a coherent specification of heading. With I pole moving with respect to the others, however, the field could yield an incoherent heading solution. Such incoherence was readily detectable; similar pole motion leading to coherent flow, however, was less readily detectable.

Adult↗

Dynamic properties of radial and tangential movements as determinants of the haptic horizontal--vertical illusion with an L figure.

In four experiments involving blindfolded subjects, constant errors in the haptic judgment of extent in the horizontal plane were found to relate consistently to the time and velocity of limb movement. Radial movements, executed at a slower speed and for a longer time, are judged longer than tangential movements of equal extent. The data were considered in relation to certain physiological and kinematic properties of the actively moving limb. Taken together with additional information on judgments of movement duration, the results suggest that the illusion of extent is modulated by the perception of differential time cues. In these terms, it was noted that the haptic horizontal-vertical illusion with the L figure is another instance of the interaction of apparent space and time commonly found in studies of psychological relativity.

Adolescent↗

Prototype formation from imaged, kinesthetically, and visually presented geometric figures.

The issue of prototype formation from simple geometric figures presented in various modes was studied in four conditions. Base figures and their exemplars were scaled in terms of their physical similarity, which was considered to reflect cognitive similarity. Geometric exemplars were visually presented, imaged by the subject, and kinesthetically presented. Following initial presentation, a recognition task was given in which some old items, some new items, and the prototype (also a new item) were presented in the same modality as originally perceived. The results indicate that prototype formation spans a wide class of human experiences and that internal representations of geometric figures derived from experiences with one modality tend to be second-order isomorphic with similar experiences derived from another modality.

Discrimination Learning↗

Motor commands and the perception of movement patterns.

Electrophysiological experiments have shown that during voluntary movement, the activity of kinesthetic receptors relevant to actively contracting muscles is modified. Furthermore, efferent motor commands interact with the central transmission and processing of kinesthetic sensory input. This article addresses itself to the question of whether the efferent motor commands of voluntary movement influence the perception and processing of kinesthetic spatial information. In two experiments, subjects moved around unfamiliar and unseen criterion stencil patterns with their right hands. In the first experiment subjects were required to concurrently track the constrained movements with their left hands. In the second experiment, following movement around a criterion pattern, the subjects had to recall it with their right hands. Tracking and recall movements in the two experiments showed a systematic spatial bias in the direction in which the right-hand constrained movements were commanded. It is argued that when a limb movement is contrained, the interaction between the efferent command pattern and the returning kinesthetic sensory input results in its position being perceived with a constant error in the direction in which the movement was commanded.

Cerebral Cortex↗

Variables influencing outflow-inflow interpretations tracking performance: predictability of target motion, transfer function, and practice.

Experimental evidence can be found in support of either outflow or inflow theories of voluntary action. Accordingly, the empirical problem becomes one of ascertaining fundamental conditions under which the dichotomy plainly manifests itself. Using a within-subjects design, six undergraduates were given pursuit tracking training. The independent variables were (a) presence or absence of regularity (predictability) in the back-and-forth motion of the target, (b) type of control stick (with attendant proprioceptive feedback) used to drive the cursor, and (c) practice. The dependent variable was the time integral of error. The following results were significant (p less than .05, two-tailed): (a) A pressure stick is better than a freely moving one when tracking a random target; this finding supports a reactive force inflow model. The converse is true for a predictable target and is therefore supportive of an outflow interpretation. (b) Regardless of kind of target motion, an unloaded stick is better than an elastically loaded one at the beginning of training (outflow support) but worse by the end of training (inflow support). It is concluded that the motor outflow versus motor inflow dispute is amenable to parametric resolution.

Cues↗

Processing resource demands of failure detection in dynamic systems.

The information-processing channels, proprioceptive versus visual, that are used to detect changes in the response of dynamic systems are investigated using a loading-task methodology. Conditions are compared in which subjects either control the dynamic system (MA mode) or monitor an autopilot controlling the same system (AU mode). Failure detection in these two modes of participation is evaluated when subjects perform the task alone and concurrently with either a tracking loading task or a mental arithmetic-memory loading task. The former task disrupted MA detection but not AU detection, whereas the converse results were obtained with the mental-arithmetic task. The results, interpreted within the framework of a structure-specific resource theory of human attention, suggest that AU detection relies exclusively on processing resources associated with perceptual/central-processing stages. MA detection in contrast relies on separate-processing resources residing in a response-related reservoir.

Automobile Driving↗

Why two eyes are better than one: the two views of binocular vision.

Despite centuries of research on the topic, the answer to the question "'Are two eyes significantly better than one, independent of stereopsis?" is still uncertain. In this investigation, steps are taken toward answering the question in a behavioral context. Three sets of experiments are reported in which human binocular and monocular performance are compared in a variety of exteroceptive and visuomotor tasks. In all of the experiments, two eyes facilitated performance. The findings suggest that the binocular system is able to detect the matching information, that is, the concordance, in the monocular optic arrays and to use that information to increase visual efficiency. Furthermore, stereopsis was not found to be important in the performance of visuomotor skills in three dimensions when the subjects were free to move their heads. Thus, the results indicate that an important ecological benefit of binocular frontal vision is having binocular concordance, rather than having binocular disparity.

Adult↗

Organization and learning of visual-motor information during different orders of limb movement: step, velocity, acceleration.

Theoretical use of the tracking paradigm as a means of understanding perceptual-motor organization has been influenced by ambiguous assumptions concerning the relation of time orders of force production to the learning and performance of time orders of limb movement. This study provides both a conceptual framework for clarifying these assumptions, and empirical data for testing them. The independent variables were (a) target motion (step, velocity, acceleration); (b) stick loading (elasticity, damping, mass); and (c) practice. The dependent variables were absolute terror for step and time-integrated squared error for velocity and acceleration. The hypothesis was that proficiency of tracking is inversely related to mathematical complexity of reactive forces, within constraints imposed by familiarity with required types of transfer functions. Five subjects were assigned to track one type of target motion in each of the three loading conditions, respectively. Cursor-present "training" trials were alternated with cursor-absent "test" trials. Thereby, a premium was placed on attention to proprioceptive feedback, at least at the start of training. The hypothesis could not be rejected.

Adult↗

Speed and accuracy of compensatory responses to limb disturbances.

This study examines the speed and accuracy of compensatory responses to flexion-extension perturbations of the wrist in the horizontal plane. In Experiments 1 and 2 the subjects were required to establish an initial flexion or extension force of approximately 15% maximum at a prescribed initial muscle length. The perturbations changed the load force by +/-5% in both simple and choice reaction protocols. The results showed that the latencies to compensate for the perturbation were longer when the direction of disturbance was unknown (i.e., choice effect) and when the perturbation unloaded the muscle (i.e., directional effect). Accuracy constraints on the compensatory response increased movement time and reduced the variability of latency without affecting mean latency. In Experiment 3, a visual stimulus generated a comparable choice effect on latency to that produced by the perturbations, but no directional effect in relation to the preload was apparent. Our behavioral analysis of compensatory responses triggered by wrist perturbations confirms that these responses are susceptible to variables that influence the initiation of voluntary movements. Our analysis also demonstrates a directional preload effect that is stimulus specific.

Adaptation, Physiological↗

Spatial and movement-based heuristics for encoding pattern information through touch.

Seven experiments investigated the heuristics people use to encode spatial pattern information through touch. Observers traced a tangible pathway with one hand and then answered questions about either the euclidean line between the pathway endpoints or the pathway itself. Parameters of the euclidean line were held constant, while characteristics of the felt pathway were manipulated. Experiments 1-4 showed that blindfolded sighted and blind observers increasingly overestimated the length of the euclidean line as the length of the explored pathway increased. This indicates a movement-based heuristic for encoding distance. Experiments 5-7 indicated that judgments of the position of the euclidean line did not vary with the position of the felt pathway or the extent to which it deviated from that line. Instead, the results indicated that observers relied on implicit spatial axes, which are movement independent, to judge position. These and other results have implications for theories of haptic encoding of spatial pattern and for the construction of tangible graphics displays.

Adult↗

Imagined spatial transformation of one's body.

This study examined two related phenomena: (a) the judgment of whether a human body part belongs to the left or right half of the body and (b) the imagined spatial transformation of one's body. In three experiments, observers made left-right judgments of a part of a body whose orientation differed from their own by a rotation about one of 13 axes. To do so, they imagined themselves passing to the orientation of the stimulus. Time for (a) left-right judgments and (b) accompanying imagined spatial transformations depended on the extent of the orientation difference (OD) between the observer and stimulus. More important, time for phenomena (a) and (b) depended strongly, and in the same way, on the direction of OD. Further results showed that the rate of imagined spatial transformations can vary strongly for different axes and directions of rotation about an axis. These and other results (e.g., Parsons, 1987a) suggest that temporal and kinematic properties of imagined spatial transformations are more object-specific than could be previously assumed.

Body Image↗

Piecemeal organization and cognitive components in object perception: perceptually coupled responses to moving objects.

In three experiments, observers who were instructed to perceive one of two alternative depth arrangements of a three-dimensional wire cube fixated near one of two intersections that differed in the degree to which they specified the cube's veridical depth organization. In order to separate perceptual effects from experimenter effects, we measured indirect reports about variables perceptually coupled to perceived depth rather than direct reports about perceived depth. In all three experiments, reversal durations at the two intersections differed, even though the two were parts of a single object. In addition, reversals varied with viewers' intentions. Thus, the unit of perceptual organization may be smaller than the entire object, and viewers' intentions can influence the perception of real moving objects. In additional analyses, reversal durations were separated into two components: nonelective instability and malleability; the question of whether these two components of ambiguity are functionally distinct could not be decided.

Depth Perception↗