Matheus M. Pacheco

Transfer as a function of exploration and stabilization in original practice

The identification of practice conditions that provide flexibility to perform successfully in transfer is a long-standing issue in motor learning but is still not well understood. Here we investigated the hypothesis that a search strategy that encompasses both exploration and stabilization of the perceptual-motor workspace will enhance performance in transfer. Twenty-two participants practiced a virtual projection task (120 trials on each of 3 days) and subsequently performed two transfer conditions (20 trials/condition) with different constraints in the angle to project the object. The findings revealed a quadratic relation between exploration in practice (indexed by autocorrelation and distribution of error) and subsequent performance error in transfer. The integration of exploration and stabilization of the perceptual-motor workspace enhances transfer to tasks with different constraints on the scaling of motor output.

Search Strategies in Practice: Movement Variability Affords Perception of Task Dynamics

ABSTRACT Practice has been conceptualized in terms of a search process through an evolving perceptual-motor workspace. The experiment was set up to examine whether the inherent variability of the system would influence perception of the relevant properties of the task space. We reanalyzed the data from Hsieh, Liu, Mayer-Kress, and Newell (2013) in which participants performed a speed-accuracy aiming task and feedback emphasized either temporal or spatial accuracy in different conditions. The maximum variability in spatial error during practice differentiated individuals best performance in the fast speed-accuracy conditions. Additionally, we found that a threshold of variability predicted discontinuities during practice within individuals. The findings support the proposition that inherent variability affords perception of the relevant dimension of the task. The search motion through the perceptual-motor workspace was continuous or discontinuous depending on the constraints of the movement speed-accuracy condition.

Adapting relative phase of bimanual isometric force coordination through scaling visual information intermittency.

Visual information plays an adaptive role in the relation between bimanual force coupling and error corrective processes of isometric force control. In the present study, the evolving distribution of the relative phase properties of bimanual isometric force coupling was examined by scaling within a trial the temporal feedback rate of visual intermittency (short to long presentation intervals and vice versa). The force error (RMSE) was reduced, and time-dependent irregularity (SampEn) of the force output was increased with greater amounts of visual information (shorter intermittency). Multi-stable coordination patterns of bimanual isometric force control were differentially shifted toward and away from the intrinsic dynamics by the changing the intermittency of visual information. The distribution of Hilbert transformed relative phase values showed progressively a predominantly anti-phase mode under less intermittent visual information to predominantly an in-phase mode with limited (almost no) visual information. Correlation between the hands showed a continuous reduction, rather than abrupt transition, with increase in visual information, although no mean negative correlation was realized, despite the tendency towards an anti-phase distribution. Lastly, changes in both the performance outcome and bimanual isometric force coordination occurred at visual feedback rates faster than the minimal visual processing times established from single limb movement and isometric force protocols.

Bimanual coordination and the intermittency of visual information in isometric force tracking

The effect of the intermittency of visual information in the bimanual coordination of an isometric force coordination task was investigated as a function of criterion force level. Eight levels of visual information intermittency (.2–25.6xa0Hz) were used in blocked fashion at each force level. Participants were required to produce a constant force output matching as accurately as possible the criterion force target. The results showed that performance improved as the intermittency of visual information was reduced—this effect being a function of force level. The distribution of the relative phase through the trial revealed a preference for the two hands to be coupled together (in-phase) at the slower rates of visual presentation (~.2xa0Hz). However, as the rate of visual feedback was increased (up to ~25.6xa0Hz), there was a transition to predominantly a negative correlation pattern (anti-phase). The pattern of bimanual coordination in this isometric tracking task is driven by the availability of information for error correction and the interactive influence of perceptual–motor constraints.

Unique perceptuomotor control of stone hammers in wild monkeys

We analysed the patterns of coordination of striking movement and perceptuomotor control of stone hammers in wild bearded capuchin monkeys, Sapajus libidinosus as they cracked open palm nut using hammers of different mass, a habitual behaviour in our study population. We aimed to determine why these monkeys cannot produce conchoidally fractured flakes as do contemporary human knappers or as did prehistoric hominin knappers. We found that the monkeys altered their patterns of coordination of movement to accommodate changes in hammer mass. By altering their patterns of coordination, the monkeys kept the strikes amplitude and the hammers velocity at impact constant with respect to hammer mass. In doing so, the hammers kinetic energy at impact—which determines the propagation of a fracture/crack in a nut—varied across hammers of different mass. The monkeys did not control the hammers kinetic energy at impact, the key parameter a perceiver-actor should control while knapping stones. These findings support the hypothesis that the perceptuomotor control of stone hammers in wild bearded capuchin monkeys is inadequate to produce conchoidally fractured flakes by knapping stones, as do humans.

Search strategies in practice: Influence of information and task constraints

The practice of a motor task has been conceptualized as a process of search through a perceptual-motor workspace. The present study investigated the influence of information and task constraints on the search strategy as reflected in the sequential relations of the outcome in a discrete movement virtual projectile task. The results showed that the relation between the changes of trial-to-trial movement outcome to performance level was dependent on the landscape of the task dynamics and the influence of inherent variability. Furthermore, the search was in a constrained parameter region of the perceptual-motor workspace that depended on the task constraints. These findings show that there is not a single function of trial-to-trial change over practice but rather that local search strategies (proportional, discontinuous, constant) adapt to the level of performance and the confluence of constraints to action.

A test of fixed and moving reference point control in posture

This study investigated two contrasting assumptions of the regulation of posture: namely, fixed and moving reference point control. These assumptions were tested in terms of time-dependent structure and data distribution properties when stability is manipulated. Fifteen male participants performed a tightrope simulated balance task that is, maintaining a tandem stance while holding a pole. Pole length (and mass) and the standing support surface (fixed surface/balance board) were manipulated so as to mechanically change the balance stability. The mean and standard deviation (SD) of COP length were reduced with pole length increment but only in the balance board surface condition. Also, the SampEn was lower with greater pole length for the balance board but not the fixed surface. More than one peak was present in the distribution of COP in the majority of trials. Collectively, the findings provide evidence for a moving reference point in the maintenance of postural stability for quiet standing.

Matching and Minimizing Movement Time in Speed-Accuracy Tasks.

The goal of present experiment was to test whether different speed-accuracy paradigms outcomes (time minimization and time matching) were due to different temporal and spatial task constraints. Fifteen participants twice performed 100 trials of time minimization and time matching tasks with the yoked temporal and spatial requirements (criterion time and target width). The results showed that performing an aiming movement under the same spatial and temporal constraints resulted in similar outcomes with distributional properties (skewness and kurtosis) being slightly affected by practice effects. There was a trade-off in the information entropy for space and time (temporal information entropy decreased as spatial information entropy increased) with practice. Nevertheless, the joint space-time entropy of outcome did not change across tasks and conditions-revealing a common level of space-time entropy between these two categories of aiming tasks. These findings support the hypothesis that under the same spatial and temporal constraints the movement speed-accuracy function shares the same properties independent of task category.

Movement Speed and Accuracy in Space and Time: The Complementarity of Error Distributions

ABSTRACT Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We investigated the space-time account of Hancock and Newell (1985) and the hypothesis of complementarity between the four moments of the error distribution in space and time. Twelve participants performed 15 conditions in a line drawing task composed of different spatial (10, 20, and 30 cm) and temporal (250 to 2,500 ms) criteria. The results showed that all moments of distributions changed systematically between conditions but there were some departures from the Hancock and Newell predictions. In contrast, individual analysis revealed the complementarity of the spatial and temporal error including a trade-off between the four moments of error. These findings support a complementary space-time account of movement speed and accuracy.

Constraints specific influences of vision, touch and surface compliance in postural dynamics

Studies that have manipulated vision and touch in posture usually emphasize the prescriptive closed-loop function of the information to reduce the amount of postural motion. In contrast, we examine here the hypothesis that the standard sensory manipulations to maintain quiet stance also change in specific ways the constraints on the task goal and the emergent movement organization. Twelve participants were instructed to maintain quiet postural stance under three sensory factors: surface compliance (foam/no foam), visual information (open/closed eyes) and tactile information (finger touch/no finger touch). The standard deviation of center of pressure (COP) motion decreased with the presence of vision, touch and rigid surface. The correlation dimension showed that the manipulation of touch and vision produced different attractor dynamics that also interacted with surface compliance. Vision decreased the correlation dimension in the foam surface while the touch manipulation increased dimension in the rigid surface. The sensory information manipulations changed the qualitative properties of the attractor dynamics as well as the quantitative properties of the amount of postural motion providing evidence for the specific nature of the postural organization across information conditions.