Papers by George Stelmach
Journal of Motor Behavior, 2006
The authors investigated whether visual fixations during a continuous graphical task were related... more The authors investigated whether visual fixations during a continuous graphical task were related to arm endpoint kinematics, joint motions, or joint control. The pattern of visual fixations across various shapes and the relationship between temporal and spatial events of the moving limb and visual fixations were assessed. Participants (N = 16) performed movements of varying shapes by rotating the shoulder and elbow joints in the transverse plane at a comfortable pace. Across shapes, eye movements consisted of a series of fixations, with the eyes leading the hand. Fixations were spatially related to modulation of joint motion and were temporally related to the portions of the movement where curvature was the highest. Gathering of information related to modulation of interactive torques arising from passive forces from movement of a linked system occurred when the velocity of the movement (a) was the lowest and (b) was ahead of the moving limb, suggesting that that information is used in a feedforward manner. Keywords coordination; limb control; oculomotor control Many of our daily activities involve coordinated motion of multiple body segments through the environment. Vision provides information about the environment, and that information is integrated with other sources of information regarding the effector's position so that we can achieve the movement goal. It is probable that the eyes move with a combination of smooth pursuit and saccadic movements. Researchers have shown that during movements that require precision, namely, identifying and preparing to manipulate objects, the eyes fixate and shift gaze several times so that they can gather information (
Journal of Functional Morphology and Kinesiology, 2021
In goal-directed movements, effective open-loop control reduces the need for feedback-based corre... more In goal-directed movements, effective open-loop control reduces the need for feedback-based corrective submovements. The purpose of this study was to determine the influence of hand preference and aging on submovements during single- and two-joint pointing movements. A total of 12 young and 12 older right-handed participants performed pointing movements that involved either elbow extension or a combination of elbow extension and horizontal shoulder flexion with their right and left arms to a target. Kinematics were used to separate the movements into their primary and secondary submovements. The older adults exhibited slower movements, used secondary submovements more often, and produced relatively shorter primary submovements. However, there were no interlimb differences for either age group or for the single- and two-joint movements. These findings indicate that open-loop control is similar between arms but compromised in older compared to younger adults.
Motor Control, 2012
This study examined how aging compromises coordinative eye-hand movements with multiple segments.... more This study examined how aging compromises coordinative eye-hand movements with multiple segments. Older adults and young controls performed two-segment movements with the eyes only or with the eyes and hand together. The results showed minimal age-related changes on the initiation and execution of primary saccade during the first segment. However, the older adults showed a scaling problem of saccade velocity when hand movements were included. They were also slow in stabilizing gaze fixation to the first target. Regarding hand movements, the older adults pronouncedly increased the deceleration phase compared with the controls while fixating their gazes to the target. They also increased the intersegment interval for both eye and hand movements. Taken together, aging differentially affects various components of movements, which contributes to the slowness of overall performance.
Human Factors: The Journal of the Human Factors and Ergonomics Society, 1969
The effect of practice on individual differences, intra-individual variability, and remoteness wa... more The effect of practice on individual differences, intra-individual variability, and remoteness was studied in performance during eight minutes of continuous practice on a large muscle motor task. Individual differences (true score variance) revealed a slight increase during the practice session, while the intra-individual variability remained relatively unaffected by massed practice. When the improvement in performance was removed by examining the relative variability, both sources of variance increased. The effects of an increasing number of interpolated trials on the inter-trial correlations revealed that with increasing amounts of remoteness, the inter-trial correlations decreased.
Human Factors: The Journal of the Human Factors and Ergonomics Society, 1992
This article reviews literature that documents the effects of age on motor performance as it rela... more This article reviews literature that documents the effects of age on motor performance as it relates to driving behavior. Movement initiation is the focal point of the first part of the article, and it is considered in terms of absolute age differences when functional manipulations are made, such as response preparation, response selection, response programming, and complexity. The second part of the article addresses age difference in the context of movement execution characteristics; differences in movement speed, force production, limb coordination, and sensory motor integration are considered. Movement time and movement kinematics and kinetics are the principal dependent measures reviewed. Adults were found to initiate and execute movements more slowly and with less precision as they age, which may contribute to the decline of their driving skill. Most of the data reviewed were obtained in laboratory settings; nevertheless, they suggest how age may impair the elderly driver.
International Journal of Neuroscience, 1987
• We examined the ability of a patient, who had a cerebral lesion involving the left posterior he... more • We examined the ability of a patient, who had a cerebral lesion involving the left posterior hemisphere, to identify and to localize stimuli applied to her "deaffe-rented" right upper limb. We observed a functional dissociation between localiza-tion and identification in both perfor-mance and subjective report. This finding may be a tactual analogue of "blind sight."
Bulletin of the Psychonomic Society, 1984
Advances in Psychology, 1983
‘Automatic’ behaviors and those requiring or utilizing attention have long been theoretical oppos... more ‘Automatic’ behaviors and those requiring or utilizing attention have long been theoretical opposites in cognitive psychology. This paper is an attempt to document the complexities involved in the development of a theoretical orientation to task automaticity when couched in terms of theories of attention. It is suggested that understanding automaticity of skills is dependent on a coherent and viable theory of attention, but only in part. Coming to theoretical grips with consciousness and learning, and their influence on motor control is also vital. Two major challenges, therefore, remain: to establish a viable theory of automaticity that includes and corresponds with (a) contemporary theories of attention and (b) control theories of motor behavior. “The discovery of attention did not result in any immediate triumph of the experimental method. It was something like the discovery of a hornet's nest: the first touch brought out a whole swarm of instant problems.”-Edward Titchener, 1908
International Journal of Neuroscience, 1987
The question addressed is whether temporal or spatial characteristics of a movement sequence are ... more The question addressed is whether temporal or spatial characteristics of a movement sequence are represented in a motor program. Subjects executed one to five straight-line strokes as fast as possible on a digitizing tablet. The duration and length of each stroke were computed and intercorrelated. Nineteen out of 20 possible correlations were significant for length per stroke data while only one of the 20 correlations was significant for duration. Further, performance data on the five stroke patterns were sorted to examine whether the first stroke determined the overall temporal/spatial pattern of the subsequent strokes executed. It was found that only sorting by length of the first stroke produced different subsets of movement patterns. These results are argued to be in support of the hypothesis that the spatial microstructure is controlled in a prepared movement sequence.
Psychonomic Science, 1968
Using a lever positioning task, six groups of 10 Ss attempted to reproduce target positions of 25... more Using a lever positioning task, six groups of 10 Ss attempted to reproduce target positions of 25 deg or 65 deg under tension levels of either 0, 5, or 10 lb. 11 was found that the accuracy of reproduction was facilitated by the increased resistence at the 65-deg target position. No increase in accuracy was found at the 25-deg target.
Bulletin of the Psychonomic Society, 1982
A partial advanced information paradigm that utilizes movement precues about upcoming movements w... more A partial advanced information paradigm that utilizes movement precues about upcoming movements was applied to flexion and extension foot movements of either a large or small extent. By analyzing reaction times obtained when precues gave either no information, partial information about either direction or extent, or complete information about movement parammeters, it was found that initiation times varied as a function of amount of advanced information. Reaction times were fastest in the complete information condition, followed by the partial and no information conditions. With regard to type of parameter to be programmed, extent was faster than direction. Further, the data suggested that direction specification and extent specification must be considered as two serially organized. interdependent, and ordered operations, with the former consuming more time than the latter. It is commonly viewed that the role of a motor program is to prescribe values on certain kinematic parameters that are under program control. In examining this prescription process, Rosenbaum (1980) extended the longstanding partial advanced information paradigm to examine the operational characteristics of motor programming. The major question addressed was how movement dimensions, such as arm, direction, and extent, are specified. Using a precuing technique, subjects were required to execute simple limb movements that varied in a number of movement dimensions (e.g., arm, direction, and extent). The precues signaled total, partial, or no information about the intended movement, and by comparing the possible combinations of precues, inferences were made about the independent and interactive roles of each movement parameter in motor program construction. From his data, Rosenbaum concluded that specifications of the various movement dimensions are serially organized operations, but without a fixed order, and that programming times are longer for arm than for direction and longer for direction than for extent. Do these results really address response programming construction? Recently, Goodman and Kelso (I 980) and Stelmach and Larish (Note 1) have criticized the technique used by Rosenbaum because it possesses a substantial cognitive-motor translation process. Rosenbaum used letters to precue the subject, and previously learned color-coded labels were signals to respond, raising the possibility that translation (verbal code to position code) processes (Teichner & Krebs, 1974) may have influenced the produced reaction times. In instances in which the reaction stimulus and its associated response are indirect and relatively unpracticed, nonmotor, cognitive pro-Reprint requests should be addressed to Michel Bonnet,
Parkinsonism & related disorders, 2006
We examined whether coordination between movement components during trunk-assisted prehension was... more We examined whether coordination between movement components during trunk-assisted prehension was compromised in PD patients in response to varying constraints (experiment 1: reach speed, object size, movement amplitude; experiment 2: movement sequence). In general, both PD patients and controls responded similarly to the changes in these three variables. PD patients, however, demonstrated less synchronized movements in terms of timing between onsets and offsets of aperture formation, endpoint motion and trunk motion. In addition, PD patients used a pattern different from that of controls in specifying the relative contribution of trunk and arm to the endpoint motion. A significant group difference was observed in that controls tended to synchronize the involved movement components together, whereas PD patients did not show such a trend. These data suggest that PD patients have intact parameterization capabilities, although they have a reduced capability to coordinate multiple neuro...
Journal of manipulative and physiological therapeutics, 1994
a) Establish a precise, standardized method to assess prone leg alignment changes (functional &qu... more a) Establish a precise, standardized method to assess prone leg alignment changes (functional "leg length inequality"), which have, until now, been reported clinically to occur as a result putative chiropractic subluxation isolation tests [neck flexion (C5) and extension (C1)]; and b) describe differences in leg alignment changes in a group of healthy subjects and patients with chronic spinal complaints. Two group, two isolation tests, descriptive, repeated measure analysis of variance. Exercise and Sport Research Institute, Arizona State University. Eight healthy controls, eight patients with a history of chronic spinal complaints and observable leg alignment reactivity. Active cervical flexion/extension maneuvers. Optoelectric markers affixed to heels and occiput, as subjects lay prone. Marker locations sampled at 100 Hz for 10 sec during: a) three no movement trials, b) three cervical extension and c) three flexion trials. Data transformed to local reference frame appro...
Advances in Psychology, 1980
Testing the hypothesis that spatial localization is made on the basis of an abstract spatial code... more Testing the hypothesis that spatial localization is made on the basis of an abstract spatial code, rather than on stored proprioceptive information, orientation of the unseen limb was contrasted under same and switched limb movement conditions. In Experiments 1 and 2, movements were executed in the midline vertically upward and horizontally away, respectively. The results of both experiments revealed that same limb accuracy was superior only at farther target positions, and it was hypothesized that orientation of the limb could be mediated by a spatial location code if movements remained within the confines of an egocentric reference system. To test this tentative assertion more directly, Experiment 3 examined same and switched limb performance in two-dimensional space. At locations defined a priori as inside egocentric space, absolute movement accuracy and amplitude error failed to differentiate between same and switched limb localization. At locations defined a priori as outside egocentric space the same limb condition prevailed. Meanwhile, irrespective of spatial position directional error revealed that same limb orientation was superior to switched limb orientation. The amplitude error findings were interpreted to mean that body referent points inside egocentric space allow for the parameterization of the necessary length-tension relationships in the agonist and antagonist muscles of either limb. The direction findings were explained in light of previous data demonstrating systematic perceptual errors in estimating the objective referents.
Motor Control, 1976
Publisher Summary This chapter discusses the central and peripheral mechanisms in motor control. ... more Publisher Summary This chapter discusses the central and peripheral mechanisms in motor control. To coordinate movement, an appropriate set of muscles must be activated in proper temporal relationship to others and an appropriate amount of inhibition has to be delivered to each of the muscles that will oppose the demanded motor act. Historically, two major theoretical attempts have been made to handle these basic requirements, one peripheral in nature and the other stressing central factors. Peripheral control theory clearly recognized the value of sensory information in movement. Coordinated motor output was considered as built up from smaller, discrete phases of movement, linked together by “chain reflexes” with sensory feedback from each phase reflexly initiating each subsequent phase. Central control theory, on the other hand, claimed that feedback from the movement was unnecessary for the elaboration of motor output. Within the realm of motor behavior, the role of feedback is primarily considered in terms of peripheral information from the various modalities providing the substrate for the detection and correction of movement errors.
International Journal of Neuroscience, 1987
Parkinsonian and neurologically normal subjects performed a finger-tapping task in which differen... more Parkinsonian and neurologically normal subjects performed a finger-tapping task in which different sequence lengths had to be executed as rapidly as possible. For each response sequence, reaction time (RT), inter-tap-intervals (ITIs) and error patterns were recorded. It was found that the RT-sequence length relationship as well as the group ITI data were different for the two groups, indicative of impaired programming in the Parkinsonian subjects. This conclusion was supported by a relative dissociation of the first and subsequent taps and by a pattern of progressively increasing errors with longer tap sequences in the Parkinsonians.
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Papers by George Stelmach