Biomedical subjects

John J Buchanan

Publications and source records attributed to John J Buchanan.

8 recordsLinked to original sources

PubMed2006

Target width scaling in a repetitive aiming task: switching between cyclical and discrete units of action.

An aiming task was used to identify the processes whereby the motor system adapted a repetitive aiming action to systematic changes in ID (ID = log(2 )(2A/W), Fitts in J Exp Psychol 47:381-391, 1954) within a single trial. Task ID was scaled in a trial by moving the outside edge of two stationary targets to produce nine different target IDs in a trail. The ID within a trial was scaled in one of two directions: (1) an increasing ID condition, starting with an ID = 3.07 and ending with an ID = 5.91; and (2) a decreasing ID condition, starting with an ID = 5.91 and ending with an ID = 3.07. An index of movement harmonicity (Guiard in Acta Psychol 82:139-159, 1993) revealed that the repetitive aiming action was harmonic in nature when task ID was 3.07, and consisted of a series of discrete segments when task ID was 5.91. This finding provides evidence for the existence of discrete and cyclical units of action that are irreducible and that may be employed independently to assemble longer continuous actions. The scaling of ID within a trial promoted a transition in repetitive aiming motions assembled from discrete and cyclical units of action. A variety of kinematic measures (e.g., movement harmonicity, time spent accelerating the limb) revealed a critical ID (ID(c)) region (4.01-4.91) separating aiming motions governed by the different units of action. Enhancement of fluctuations before the transition were found in the movement harmonicity data and in the distance traveled to peak velocity data, with variability in these measures highest in the ID(c) region. The enhancement of fluctuations indicates that loss of stability in the limb's motion acted as a key mechanism underlying the transition between units of action. The loss of stability was associated with the transition from cyclical to discrete actions and with the transition from discrete to cyclical actions. The transition between units of action may be conceptualized as a transition from a limit cycle attractor (cyclical unit of action) to a shift between two fixed-point attractors (discrete unit of action) when ID was increased, with the transition occurring in the opposite direction when ID was decreased.

Adaptation, Physiological↗

PubMed2006

One-to-one and polyrhythmic temporal coordination in bimanual circle tracing.

The authors manipulated movement amplitude in a bimanual circle-tracing task to alter the natural tracing frequency of the arms. Participants (N = 14) traced different-diameter circles simultaneously with the two arms in either in-phase (0 degrees) or antiphase (180 degrees) coordination, using the index fingers or plastic styli. Movement amplitude altered the natural tracing frequency of the arms, as demonstrated by the following 2 findings: (a) The larger the difference in circle diameter, the larger was the shift from the fixed-point values of 0 degrees and 180 degrees, and the shift increased as movement frequency increased. Those results are consistent with the manipulation of delta omega in the bimanual pendulum paradigm. (b) Increasing movement frequency induced transitions from 1:1 to non-1:1 coordination, contrary to findings in previous investigations of polyrhythmic coordination. Tactile feedback played a minimal role in stabilizing bimanual coordination in the current tasks.

Adult↗

PubMed2005

The interaction of tactile information and movement amplitude in a multijoint bimanual circle-tracing task: phase transitions and loss of stability.

Adaptive behaviour in bimanual coordination was examined with the use of a bimanual circle-tracing task. Circle diameter and tactile information were manipulated to form four tracing conditions: tracing a pair of 3-cm diameter circles with the tips of the index fingers (3F) or hand-held styli (3S) and tracing a pair of 10-cm diameter circles with the tips of the index fingers (10F) or hand-held styli (10S). Movement frequency was increased in all conditions. In the 3F, 3S, and 10S tracing conditions, an abrupt transition from asymmetric to symmetric coordination was the main adaptive response, while in the 10F tracing condition, phase wandering was the main adaptive response. Enhancement of fluctuations in relative phase, a signature of loss of stability, occurred before the transition from asymmetric to symmetric coordination. Movement frequency and movement amplitude interact as control parameters in this task. The results are discussed with reference to tactile surface contact and joint motion as sources of sensory information that can be used to stabilize bimanual coordination patterns. The presence or absence of tactile information is directly linked to the specific form of adaptive behaviour (phase transition or phase wandering) that emerges as a function of required movement amplitude and required pacing frequency.

Adult↗

PubMed2004

Systematic scaling of target width: dynamics, planning, and feedback.

The target width of a single target in a two-target reciprocal aiming task was scaled from small (ID = 5.85) to large (ID = 2.85) and large-to-small within individual trials with movement amplitude fixed. Scaling target width produced a transition in the end-effector's dynamics and based on a measure of movement harmonicity, the transition was sensitive to the initial conditions but not to the direction of target width scaling. Hysteresis emerged in a variety of kinematic measures suggesting that the interdependency of planning and feedback control processes was sensitive to initial conditions as well as the direction of target width scaling. Practice increased the efficiency of the reciprocal movements and produced changes in movement time and the measure of harmonic motion that revealed a tuning of the end-effector's dynamics to cyclical motion over as large of range of IDs as possible. The tuning occurred through the modulation of time spent accelerating and decelerating the end-effector for IDs outside the range of 3.85-4.26. The results are discussed with reference to a critical ID boundary that separates regions of parameter space wherein the end-effector's dynamics are more cyclical (limit-cycle) or discrete (fixed-point) in nature.

Acceleration↗

PubMed2004

Amplitude scaling in a bimanual circle-drawing task: pattern switching and end-effector variability.

The authors manipulated movement amplitude in a bimanual circle-tracing task performed by 11 participants. With pacing frequency fixed, the systematic increase and decrease of circle diameter within a trial induced phase transitions from the asymmetric (33% of trials) to the symmetric bimanual circle-tracing pattern; the transitions resulted from a loss of stability in the asymmetric pattern. Tracing frequency varied inversely with circle diameter so that end-effector variability was minimized in a set of self-paced trials in which the circle diameter in a trial was fixed. In the amplitude-scaling trials, end-effector variability varied directly with circle diameter, a consistent speed-accuracy tradeoff. The results support the conclusion that movement amplitude is a nonspecific control parameter. The findings are discussed with reference to several factors, e.g., tactile feedback, the recruitment and suppression of biomechanical degrees of freedom, and the role those factors may play in stabilizing bimanual coordination patterns

Adult↗

PubMed2003

Learning a single limb multijoint coordination pattern: the impact of a mechanical constraint on the coordination dynamics of learning and transfer.

The coordination dynamics of learning and transfer were studied in a single limb multijoint task requiring rhythmic elbow and wrist motions. Participants were required to learn a continuous 90 degrees relative phase pattern between the elbow and wrist such that an angle-angle plot of elbow and wrist motion produced a circle with a diameter of 80 degrees. Joint motion was restricted to elbow and wrist flexion-extension on the sagittal plane and the to-be-learned 90 degrees relative phase pattern was always practiced with the learning arm supine. Cycling frequency was controlled by a pacing metronome set at 0.75 Hz. Issues regarding effector-independent and effector-specific transfer were addressed with three transfer conditions: (1). learning arm prone (LP), (2). non-learning arm supine (NS), and (3). non-learning arm prone (NP). Four subjects learned the required relative phase (90 degrees ) and amplitude (80 degrees ) pattern with their dominant arm and four with their non-dominant arm. The experiment produced three main findings with regard to elbow-wrist control processes: First, seven of eight participants spontaneously produced a wrist-lagging coordination pattern (wrist motion lagged elbow motion) in learning to produce a continuous relative phase pattern of 90 degrees between the elbow and wrist. The wrist-lagging pattern may emerge as a result of the central nervous system exploiting the transfer of angular momentum from the elbow to the wrist as the elbow rotates up and down. The influence of interactive torque on elbow-wrist coordination represents an important mechanical constraint on the selection of intralimb coordination strategies during learning. The transfer conditions revealed that this mechanical constraint was effector-independent with regard to ipsilateral limb transfer (LP) and contralateral limb transfer (NS and NP). Second, consistent transfer of the learned relative phase pattern across ipsilateral and contralateral conditions demonstrates an effector-independent representation for this control variable. The effector-independent and effector-specific nature of joint amplitude transfer was dependent to some degree on learning arm, dominant or non-dominant, and the amount of practice, 1 day versus 5 days. Third, learning of the required 90 degrees relative phase pattern may be characterized as a phase transition leading to the formation of a stable attractor in the elbow-wrist coordination landscape. The above findings are discussed with respect to motor programming and coordination dynamic viewpoints on effector-independent and effector-specific aspects of motor equivalence.

Adult↗

PubMed2003

Voluntary control of postural equilibrium patterns.

The ability to voluntarily transit from one whole-body movement to another is based on the multisensory integration of visual, vestibular, and somatosensory information. The role of functional sensory ranges and mechanical constraints on the ability to voluntarily transit between whole-body movements was studied by requiring subjects to switch from a head-fixed-to-surface to head-fixed-in-space postural pattern (and vice versa). The head-fixed-to-surface pattern required an erect stance characterized by an in-phase relationship between center of pressure (CoP) and platform motion. The head-fixed-in-space pattern required subjects to fix trunk-head position in-space while producing an anti-phase relationship between CoP and platform motion. The voluntary transition was performed with and without vision while standing on a surface oscillating in the anterior-posterior (A/P) direction. The support surface oscillated at five frequencies (0.2-1Hz) with amplitude fixed at 15cm. The voluntary transition was initiated with an auditory cue. The appropriate CoP-platform phase relationship for the two postural patterns was produced for all frequencies with and without vision. Upper-trunk kinematics revealed that subjects often failed to produce the head-fixed-to-surface pattern for frequencies >/=0.6Hz, while producing the head-fixed-in-space pattern at all frequencies with vision. Without vision, neither pattern was produced consistently based on upper-trunk kinematics. These findings demonstrate separate control processes for upper- and lower-body motion and that functional sensory ranges and mechanical constraints can facilitate or inhibit voluntary production of whole-body movements based on these control processes. The results are discussed in reference to neurological substrates that may be involved in the planning and execution of motor set-switching. The experimental protocol we employ may also have application as a diagnostic tool for the evaluation of postural deficits.

Adaptation, Physiological↗

PubMed2003

Discrete and cyclical units of action in a mixed target pair aiming task.

Two experiments addressed the issue of discrete and cyclical units as possible basic units of action that might be used to construct complex actions based on task constraints. The experiments examined the influence of low and high accuracy constraints on the end-effector's motion in rhythmical aiming movements. Both experiments utilized a Fitts-type task under three accuracy constraints: (1) big target pairing-low index of movement difficulty (ID), (2) small target pairing-high ID, and (3) mixed target pairing-one target high ID and the other target low ID. Experiment I was a 1-degree-of-freedom ( df) task that required subjects to crossover the inside edge of targets in a target pair using elbow flexion-extension motions. Experiment II used a 2- df task that required subjects to tap back and forth between targets in a target pair using a hand-held stylus. In both experiments, end-effector motion in the low ID condition was cyclical with the end-effector's motion consistent with a limit-cycle attractor description, while in the high ID condition end-effector motion was discrete and consistent with a fixed-point attractor description. The mixed target pairing produced both discrete and cyclical features in the end-effector's dynamics that suggested a functional linking of discrete and cyclical units of action as the optimal movement solution. Evidence supporting the above statements was found in the kinematic measures of movement time (MT), dwell time, proportion of MT accelerating and decelerating, and in a measure of harmonicity (Guiard 1993, Acta Psychol 82:139-159; Guiard 1997, Hum Mov Sci 16:97-131). Extended practice in the mixed target condition revealed a bias towards cyclical motion with practice. The results demonstrate that discrete and cyclical motion, represented as limit-cycle and fixed-point attractors, are basic units of action that the motor system uses in constructing more complex action sequences. The results are discussed with reference to coordinative structures and the generalized motor program as basic units of action. Issues pertaining to visual feedback processing and movement braking in rapid aiming tasks are also discussed.

Acceleration↗