Eric L. Amazeen

Weight Perception and the Haptic Size-Weight Illusion Are Functions of the Inertia Tensor

The complex effects of mass and volume on weight perception (e.g., the size-weight illusion) were hypothesized to follow simply from invariants of rotational dynamics. In Experiments 1-3, the rotational inertia of wielded, occluded objects was varied independently of mass, size, and torque. Perceived heaviness depended only on rotational intertia. Reanalysis of J. C. Stevens and L. L. Rubins (1970) study revealed that sizes influence on weight perception depends on specific patterns of the eigenvalues of the inertia tensor. These patterns were simulated in Experiments 4-6 with objects of fixed mass, volume, and visible size. Perceived heaviness decreased and increased, respectively, over object sets with the eigenvalue patterns of (a) constant mass, increasing volume and (b) increasing mass, constant volume. Weight perception and the size-weight illusion depend on stimulus invariants, not inference.

Attention and Handedness in Bimanual Coordination Dynamics

Predictions concerning the effects of handedness and attention on bimanual coordination were made from a dynamical model that incorporates the bodys lateral asymmetry. Both handedness and the direction of attention (to the left or right) were manipulated in an inphase 1:1 frequency locking task. Left-handed and right-handed participants had to coordinate the planar oscillations of 2 handheld pendulums while 1 pendulum oscillated between spatial targets positioned over either the left or right hand. Predictions from the model were that participants would show a phase lead with the preferred hand, and that, although the phase lead would be greater when attention was directed to the preferred hand, the variability of relative phase would be lower. Confirmation of these predictions suggests that the dynamical perspective offers the possibility of studying handedness and attention without compromising theoretical precision or experimental control.

Diffusive, Synaptic, and Synergetic Coupling: An Evaluation Through In-Phase and Antiphase Rhythmic Movements.

The in-phase and antiphase patterns of interlimb l:1 frequency locking were contrasted with respect to models of coordination dynamics in biological movement systems that are based on diffusive coupling, synaptic coupling, and synergetic principles. Predictions were made from each model concerning the stable relative phase phi between the rhythmic units, its standard deviation SDphi and the self-chosen coupled frequency omegasubc;. The experimental task involved human subjects oscillating two handheld pendulums either in-phase or antiphase. The eigenfrequencies of the two hand-pendulum systems were manipulated by varying the length and mass of each pendulum individually. Relative to an eigenfrequency difference of Delta equal to zero, |Deltaomega| > 0 displaced phi from phi = 0 and phi = pi, and amplified SDphi. omegasubc; decreased with |Deltaomega|. Both the displacement of phi and SDphi were greater in the antiphase mode. Additionally, the displacement of phi increased more sharply with |Delta| for antiphase than for in-phase coordination. In contrast, omegasubc; was identical for the two coordination modes. Of the models of interlimb coordination dynamics, the synergetic model was the most successful in addressing the pattern of dependencies of phi and SDphi. The specific forms of the functions relating omegasubc; and phi to Deltaomega pose challenges for all three models, however

Perceptual independence of size and weight by dynamic touch.

Historically, the existence of a size-weight illusion has led to the conclusion that perceptions of size and weight are not independent. A dependence of perceived heaviness on physical volume (perceptual separability), however, is different from a dependence on perceived volume (perceptual independence). Three experiments were conducted to evaluate perceptual independence. The relations between perceived size and weight and physical size and mass were evaluated in Experiment 1. Perceived weight, length, and width were structured only by the corresponding physical variables, whereas variations in volume were not separable from variations in mass. F. G. Ashby and J. T. Townsends (1986) test for perceptual independence was applied in Experiment 2. Perceived weight was independent of perceived length and volume. Experiment 3 used a magnitude estimation paradigm to investigate the extent to which information-perception relations could be related to the observed patterns of separability and independence.

Predicting the nonlinear shift of stable equilibria in interlimb rhythmic coordination

Abstract A major prediction of the elementary coordination dynamics of two contralateral limb segments in 1:1 frequency locking was tested. A shift in stable steady-state relative phase φ from 0 and π radians is induced by a difference Δω in the uncoupled frequencies of the segments. The elementary coordination dynamics, an order parameter equation in φ, predicts that equilibrium shift will be a third-order polynomial function of Δω with a cubic coefficient that is 1. (a) positive when the control parameter is constant 2. (b) negative when the control parameter decreases with Δω. The prediction was confirmed in an experiment that manipulated Δω through differential loadings and the control parameter through coupled frequency. Implications for the dynamical modelling of coordination were discussed.

Coupling of breathing and movement during manual wheelchair propulsion

The hypothesis of this study was that stable coordination patterns may be found both within and between physiological subsystems. Many studies have been conducted on both monofrequency and multifrequency coordination, with a focus on both the frequency and phase relations among the limbs. In the present study, locomotor-respiratory coupling was observed in the maintenance of small-integer frequency ratios (2:1, 3:1, and 4:1) and in the consistent placement of the inspiratory phase just after the onset of the movement cycle during wheelchair propulsion. Level of experience and various motor and respiratory parameters were manipulated. Coupling was observed across levels of experience. Increases in movement frequency were accompanied by a shift to larger-integer ratios, suggesting that a single modeling strategy (e.g., the Farey tree; D. L. González & O. Piro, 1985) may be used for coordination both within the motor subsystem and between it and other physiological subsystems.

Breaking the Reflectional Symmetry of Interlimb Coordination Dynamics

Interlimb rhythmic coordination is reflectionally symmetric when the left and right limb segments are identical in uncoupled frequencies and spatial orientation. In the present studies (4 experiments, with a total of 31 participants), when reflectional symmetry was broken through differences in timing (frequency), the resulting stable states were related by reflection and were identical for paired identically oriented limb segments behaving either as inverted or as ordinary pendulums. When reflectional symmetry was broken both temporally and spatially (coordinating inverted and ordinary pendular motions), the resulting stable states were different from those produced by identically oriented pendulums but nevertheless were related by reflection. In the Discussion, the authors focus on (a) symmetry breaking as leading to one of a number of symmetrically related states and (b) extending coordination dynamics with reflectional symmetry so that temporal and spatial asymmetries can both be accommodated.

Perceived Heaviness Is Influenced by the Style of Lifting

This experiment examined the influence of action on weight perception and the size-weight illusion. Participants rated the perceived heaviness of objects that varied in mass, length, and width. Half of the participants lifted each object and placed it down on the table and half placed the object on a pedestal before reporting their perception of heaviness. These tasks were performed either with or without vision. In all cases, increases in size produced decreases in perceived heaviness. For increases in both length and width, the use of vision produced a greater decrease in perceived heaviness. For increases in width alone, the task in which participants placed the object on a pedestal (a task for which the width of the object was a relevant variable) was associated with a greater decrease in perceived heaviness. Salience of information was discussed as a means by which task and modality might influence perception.

Timing the selection of information during rhythmic catching

Catching a ball requires that information be available close to the catch but early enough for prospective or corrective control. In the present experiment, 6 participants were asked to throw and catch a ball continuously for 1 min while wearing liquid-crystal goggles that restricted viewing to specific amounts of time at specific intervals. Participants were free to select the information by varying the frequency and phasing of throwing relative to the goggles. Video analysis revealed that they elected a frequency of throwing that matched the goggle frequency and chose to view the ball at or around its zenith. Earlier portions of the balls trajectory were viewed as the goggle frequency increased. Despite variations in the viewing location, participants elected to view the ball on average 365 ms before the catch. Analysis of the hands trajectory further revealed that the time interval (M = 82 ms) between the balls zenith and the initiation of the final motion of the hand toward the catch did not vary as a function of the frequency of throwing. The authors conclude that the timing constraints imposed by the hands movement are the basis for the selection of information for catching.

Perception-action and the Müller-Lyer illusion: amplitude or endpoint bias?

Over the past decade there has been a great deal of controversy regarding the relative impact of visual illusions on cognitive judgments and the control of goal-directed action. We report the results of two experiments indicating that perceptual biases associated with the Müller-Lyer illusion involve a misjudgment of amplitude/extent while aiming biases involve error in the specification of a movement endpoint. This dissociation of perception and action is consistent with some aspects of Milner and Goodale’s two visual system model, but not others.