Perceptual coherence in the face of discrepant multisensory signals is achieved via the processes... more Perceptual coherence in the face of discrepant multisensory signals is achieved via the processes of multisensory integration, recalibration and sometimes motor adaptation. These supposedly operate on different time scales, with integration reducing immediate sensory discrepancies and recalibration and motor adaptation reflecting the cumulative influence of their recent history. Importantly, whether discrepant signals are bound during perception is guided by the brains' inference of whether they originate from a common cause. When combined, these two notions lead to the hypothesis that the time scales on which integration and recalibration (or motor adaptation) operate are associated with different time scales of evidence about a common cause underlying two signals. We tested this prediction in a well‐established visuo‐motor paradigm, in which human participants performed visually guided hand movements. The kinematic correlation between hand and cursor movements indicates their common origin, which allowed us to manipulate the common‐cause evidence by titrating this correlation. Specifically, we dissociated hand and cursor signals during individual movements while preserving their correlation across the series of movement endpoints. Following our hypothesis, this manipulation reduced integration compared with a condition in which visual and proprioceptive signals were perfectly correlated. In contrast, recalibration and motor adaption were not affected by this manipulation. This supports the notion that multisensory integration and recalibration deal with sensory discrepancies on different time scales guided by common‐cause evidence: Integration is prompted by local common‐cause evidence and reduces immediate discrepancies, whereas recalibration and motor adaptation are prompted by global common‐cause evidence and reduce persistent discrepancies.
Psychological Research-psychologische Forschung, Aug 6, 2021
Psychologische Forschung started as a journal "für Psychologie und ihre Grenzgebiete" and became ... more Psychologische Forschung started as a journal "für Psychologie und ihre Grenzgebiete" and became strongly associated with the Berlin school of Gestalt psychology. Parallel to the fate of that school, the Journal was discontinued after 1938 and reappeared only 1949. A number of years with variable and broad editorial boards and without a clear profile followed. In 1974 the Journal switched to English as the first German psychology journal and became Psychological Research. Gradually and without any abrupt changes-as indicated e.g. by analyses of citing and cited journals-the current profile as "An International Journal of Perception, Attention, Memory, and Action" was developed. During the last one to two decades the number of papers, the number of contributing countries, and the impact increase.
Bewegungen mit indirekter Sicht im Altersverlauf · Ältere Arbeitnehmer · Zielbewegungen · Indirek... more Bewegungen mit indirekter Sicht im Altersverlauf · Ältere Arbeitnehmer · Zielbewegungen · Indirekte Sicht · Visumotorische Transformationen Zusammenfassung Präzise Zielbewegungen werden im höheren Berufs-und Le-bensalter langsamer, vor allem bei größerer Weite und höhe-ren Genauigkeitsanforderungen. Darüberhinaus findet sich eine Tendenz zu kürzeren Bewegungen. Besondere Schwie-rigkeiten entstehen möglicherweise bei Bewegungsaufgaben mit indirekter Sicht, etwa bei der Steuerung eines Mauszeigers auf einem Bildschirm oder bei minimal-invasiven chirurgischen Eingriffen. Die bisher vorliegenden Untersuchungen zum Altersverlauf der Anpassung an neue visumotorische Trans-formationen ergeben ein eher inkonsistentes Bild. Die Anpas-sung wird nicht generell schlechter, sondern Alters-veränderungen hängen offenbar von noch weitgehend unbe-kannten Randbedingungen ab. Zu diesen zählen wahrschein-lich die Art der von einer Anpassung beanspruchten Prozes-se, die Art der visumotorischen Transform...
The purpose of this paper is to argue for a particular view of motor learning which is derived fr... more The purpose of this paper is to argue for a particular view of motor learning which is derived from two different sets of data. The first set stems from studies of interference between motor tasks on the one hand and tasks of a more cognitive nature on the other hand, which are simultaneously performed at different stages of training of the motor task. As is evident from the early work of Mohnkopf (1933) and Bahrick and Shelly (1958), the original aim of these studies was to trace the time course of automation. The second set of data stems from correlational studies of individual differences. Originally, these studies were concerned with the prediction of training success in motor tasks, and for this purpose motor performance at different levels of skill was correlated with a variety of other test scores.
Zeitschrift für experimentelle und angewandte Psychologie, 1991
In two experiments the effects of binocular vergence, head tilt, and prolonged gaze inclination o... more In two experiments the effects of binocular vergence, head tilt, and prolonged gaze inclination on the preferred vertical gaze direction were studied. Concurrently, dark vergence was measured to test a hypothesis on the effect that binocular vergence has on the preferred vertical direction of gaze. The previously reported influence of observation distance on the preferred gaze inclination was replicated. When the head was tilted backward, the preferred gaze inclination was lower and the effect of observation distance was reduced; when the head was tilted forward, the preferred gaze inclination was higher and the effect of observation distance was increased. After prolonged upward or downward gaze inclination the preferred vertical gaze direction was shifted up or down, respectively, while the effect of observation distance remained constant. Overall the change of the preferred vertical direction of gaze upon binocular fixation of near stimuli was accompanied by a reduced discrepancy...
Summary In view of the discrepancy between the simple movements usually studied in the laboratory... more Summary In view of the discrepancy between the simple movements usually studied in the laboratory and complex everyday-life motor skills questions arise about generalization. It is argued that generalizability depends on different conditions for different kinds of statements. Generalization of experimental results seems to require a high similarity of the experimental situation to a reference situation, while generalizationi of theoretical statements requires invariance of the system, that is, invariance of functionally defined compnents and their interrelations. Whether or not the conditions required for generalization are fulfilled can never be established a priori, but rather a research strategy is necessary that permits this to be decided a posteriori.
Abstract 1. start with a brief description of the phenomenon [the invariance of relative timing i... more Abstract 1. start with a brief description of the phenomenon [the invariance of relative timing in human movement] and its incorporation into a particular kind of theory, the notion of a generalized motor program/several points of criticism will be discussed that can be raised ...
Publisher Summary Dual-task performance is a field of study where basic and applied research merg... more Publisher Summary Dual-task performance is a field of study where basic and applied research merges. This chapter presents three-step development in dual-task performance. With the development, dual-tasks as a method for the study of general individual-task characteristics, such as automaticity or mental load become obsolete. Instead dual-tasks become a useful method for the study of structures or functions involved in the performance of individual tasks. A final step in the theoretical and methodological development is to apply a more fine-grained analysis to dual-task performance. An adapted control system should realize selectivity, coupling among different output devices, and protection of ongoing outputs. Such adaptation, of course, will turn out to be detrimental to performance in many dual-tasks. Whenever dual-tasks require physically incompatible actions, the available time has to be split between the different tasks. In general, the time-sharing of physically incompatible actions has not attracted very much research effort, but there are exceptions such as monitoring of several different displays.
Publisher Summary To a large extent, coordination depends on the purpose of an action. Mostly, ho... more Publisher Summary To a large extent, coordination depends on the purpose of an action. Mostly, however, the purpose does not specify the required coordination uniquely. Some kinds of coordination are difficult or even impossible to achieve. Thus, in addition to voluntary constraints, there are structural limitations, and within the range of possible coordinative patterns left by voluntary constraints and structural limits, a choice has to be made. This chapter outlines the general perspective on coordination and describes the effects of voluntary constraints and the choice problem. The chapter provides an extended discussion of structural constraints. The models of coordination are presented in the chapter.
Vergence of the eyes in the dark depends on the vertical direction of gaze. In three experiments ... more Vergence of the eyes in the dark depends on the vertical direction of gaze. In three experiments this phenomenon was studied using eye inclinations and head tilts of 5min duration during which monocular or binocular near and distant stimuli were inspected. The effects of eye inclination and head tilt on dark vergence were temporally stable; they exhibited even a tendency to increase with the passage of time. On return to horizontal gaze, positive aftereffects were found, that is. dark vergence was biased towards its value with a vertically deviated gaze. The effect of vertical gaze direction turned out to be additive to the effect of binocular near fixation. These findings represent evidence against the hypothesis that the effect of vertical gaze direction on dark vergence is mediated by a feedforward signal that is related to voluntary effort in raising or depressing the eyes.
Zeitschrift für Arbeits- und Organisationspsychologie A&O, 2007
Zusammenfassung. Von Rosenstiel (2004) hat eine Diskussion zur Fachkultur der Arbeits- und Organi... more Zusammenfassung. Von Rosenstiel (2004) hat eine Diskussion zur Fachkultur der Arbeits- und Organisationspsychologie angestoßen. In dieser Diskussion wurde eine starke Abgrenzung gegen die Grundlagenfächer sowie eine spezifische Publikationskultur gefordert. Beide Entwicklungen bergen Gefahren für das Fach. Die Abgrenzung gegen die Grundlagenfächer sollte durch ein Kontinuum unterschiedlich anwendungsnaher Forschung ersetzt werden; dem entspricht eine überwiegend internationale Publikationstätigkeit, ergänzt durch deutschsprachige wissenschaftliche und anwendungsorientierte Schriften.
A theoretical framework is outlined, according to which structural constraints on bimanual moveme... more A theoretical framework is outlined, according to which structural constraints on bimanual movements can at least in part be understood as coupling between parameters of generalized motor programs. This framework provides a conceptual link between reaction-time data from experiments with bimanual responses, successive unimanual responses, and choice between left-hand and right-hand responses on the one hand and performance data obtained with concurrently performed continuous movements or sequences of discrete responses on the other. On the basis of data obtained with different methods for the study of intermanual interactions, a distinction is drawn between steady-state and transient constraints, and the hypothesis that the tendency to coactivate homologous muscles originates from a transient coupling of program parameters is applied to a variety of observations on performance in different tasks. Finally, the notion of transient constraints is applied to other types of intermanual interdependencies and to interpersonal coordination; the possible emergence of transient constraints from steady-state constraints through progressive development of inhibitory pathways in childhood is discussed, as is the potential biological significance of transient constraints.
The kinematics of leftward and rightward movements are different. The question is raised whether ... more The kinematics of leftward and rightward movements are different. The question is raised whether these differences in both arms are best accounted for in terms of the flexion-extension dimension or the leftward-rightward dimension. In a simple step-tracking experiment the acceleration-time curves of fast flexions and extensions of the left and of the right elbow joint in a horizontal plane were
Evidence for invariant relative timing is mostly based on comparisons between experimental condit... more Evidence for invariant relative timing is mostly based on comparisons between experimental conditions which differ in the average speed of the movements under study. The present experiment examines whether spontaneous variability of acceleration-time curves of aiming movements within a single experimental condition can also be described in terms of variable scaling parameters for both dimensions. This requires that the correlations between peak acceleration and peak deceleration, as well as those between time intervals defined by peak values and zero crossings, are high. In extensions of the elbow joint on a horizontal plane, the latter correlations turned out to be small or even negative. These results cannot be explained as being due to artifacts of several origins. To reconcile them with those based on comparisons between experimental conditions, a dual-level hypothesis of control in aiming movements is suggested. Only variability on one level can be described in terms of variable scaling parameters, and whether or not variability of acceleration-time curves can be described in this way depends on the relative contributions of both levels of control.
Intermanual interactions are modulated by task requirements in the course of motor preparation. I... more Intermanual interactions are modulated by task requirements in the course of motor preparation. In particular, amplitude coupling is strong when identical amplitudes are specified concurrently for the 2 hands but relaxed when different amplitudes are specified. Similarly, directional coupling is symmetric when symmetric directions are specified concurrently but turns to parallel when parallel directions are specified. Here, the author investigated whether the modulations of amplitude coupling and directional coupling in the course of motor preparation are independent or interact. Application of the timed-response procedure, which enables one to manipulate the time available for motor preparation, in 9 participants revealed a weakly interactive pattern. Directional coupling tended to be reduced when different rather than same amplitudes were specified concurrently, and amplitude coupling tended to be reduced when parallel rather than symmetric directions were specified concurrently. In general, interactive effects were also apparent in the rates at which directions and amplitudes were specified. Those observations are consistent with the notion that intermanual amplitude and direction interference are mediated by different but partially overlapping neural structures.
Robotic guidance as a means to facilitate motor learning and rehabilitation has received consider... more Robotic guidance as a means to facilitate motor learning and rehabilitation has received considerable attention during the last few years. However, mixed outcomes suggest that the benefits might be restricted to certain movement characteristics. The authors investigate the effects of robotic guidance on different kinds of motor timing. Two groups of participants performed 2 variants of a circle drawing task in a synchronization-continuation paradigm. One variant was continuous circle drawing (emergent timing), the other variant was intermittent circle drawing (event-based timing). The total duration of movement cycles (absolute timing) and the relative duration of submovements (relative timing) were measured. Half of the participants in each group were guided by a robot device during synchronization (robot-guided group), the other half of the participants received no guidance (control group). Guided participants had superior performance during the synchronization phase with both timing tasks. During continuation there were no benefits of haptic guidance anymore with the continuous circle drawing task. In contrast, with the intermittent circle drawing task guided participants were more accurate in their relative timing than control participants already in the first few trials, and this advantage did not increase in the course of practice. The benefit is thus rather immediate and not cumulative. This finding is consistent with the notion that movement characteristics such as relative timing, which are hard to demonstrate visually or verbally, profit from robotic guidance because of the more accurate demonstrations of the correct movements.
Measurements serve a purpose (and are not a purpose in themselves). This conclusion of Annett is ... more Measurements serve a purpose (and are not a purpose in themselves). This conclusion of Annett is perhaps true for science in general. And it is certainly true for the myriad of measurements taken by the sensory receptors humans are equipped with. Although it is not common to refer to the signals they provide as measurements, for the present purpose I shall call them `natural measurements’. The very fact that humans survive gives evidence of their validity. Consider the problem of assessing the slipperiness of diVerent surfaces an object can be equipped with. Human ®ngertips contain excellent sensors for slipperiness, so one might obtain subjective ratings which are likely to be based on the natural measurements they supply. However, the support of subjective ratings is certainly not the purpose these sensors have evolved for. Subjective ratings are aVected by a number of problems discussed by Annett, but these problems seem not to be rooted in the quality of the natural measurements, but in their calibration and communication which critically involve consciousness and the mapping of states of consciousness on number continua. Therefore, to avoid these problems, would it not be feasible to access the natural measurements not via conscious experience, but via their eVects on those physiological and/or behavioural processes which to support is the purpose they have evolved for? The sensors of the ®ngertips serve the regulation of grip force (cf. Johansson 1996 for an overview). Thus, it should be possible to measure grip forces while objects equipped with diVerent surfaces are lifted and thereby to exploit the natural measurements for the assessment of slipperiness. At least some natural measurements have a characteristic that makes them particularly suited for ergonomics purposes. An example is natural measurement of joint angles, provided by receptors in the joints, ligaments, tendons and muscles. If joint angles are not uniquely speci®ed by the task, humans prefer certain angles over others; speci®cally they tend to avoid the extremes of the range. Formally, this characteristic can be captured by means of cost functions (e.g. Cruse 1986). Even when it is not possible to specify the nature of such costs, the notion of cost functions is useful to capture the fact that certain joint angles are preferredÐwhere costs are lowÐand others are avoidedÐ
Perceptual coherence in the face of discrepant multisensory signals is achieved via the processes... more Perceptual coherence in the face of discrepant multisensory signals is achieved via the processes of multisensory integration, recalibration and sometimes motor adaptation. These supposedly operate on different time scales, with integration reducing immediate sensory discrepancies and recalibration and motor adaptation reflecting the cumulative influence of their recent history. Importantly, whether discrepant signals are bound during perception is guided by the brains' inference of whether they originate from a common cause. When combined, these two notions lead to the hypothesis that the time scales on which integration and recalibration (or motor adaptation) operate are associated with different time scales of evidence about a common cause underlying two signals. We tested this prediction in a well‐established visuo‐motor paradigm, in which human participants performed visually guided hand movements. The kinematic correlation between hand and cursor movements indicates their common origin, which allowed us to manipulate the common‐cause evidence by titrating this correlation. Specifically, we dissociated hand and cursor signals during individual movements while preserving their correlation across the series of movement endpoints. Following our hypothesis, this manipulation reduced integration compared with a condition in which visual and proprioceptive signals were perfectly correlated. In contrast, recalibration and motor adaption were not affected by this manipulation. This supports the notion that multisensory integration and recalibration deal with sensory discrepancies on different time scales guided by common‐cause evidence: Integration is prompted by local common‐cause evidence and reduces immediate discrepancies, whereas recalibration and motor adaptation are prompted by global common‐cause evidence and reduce persistent discrepancies.
Psychological Research-psychologische Forschung, Aug 6, 2021
Psychologische Forschung started as a journal "für Psychologie und ihre Grenzgebiete" and became ... more Psychologische Forschung started as a journal "für Psychologie und ihre Grenzgebiete" and became strongly associated with the Berlin school of Gestalt psychology. Parallel to the fate of that school, the Journal was discontinued after 1938 and reappeared only 1949. A number of years with variable and broad editorial boards and without a clear profile followed. In 1974 the Journal switched to English as the first German psychology journal and became Psychological Research. Gradually and without any abrupt changes-as indicated e.g. by analyses of citing and cited journals-the current profile as "An International Journal of Perception, Attention, Memory, and Action" was developed. During the last one to two decades the number of papers, the number of contributing countries, and the impact increase.
Bewegungen mit indirekter Sicht im Altersverlauf · Ältere Arbeitnehmer · Zielbewegungen · Indirek... more Bewegungen mit indirekter Sicht im Altersverlauf · Ältere Arbeitnehmer · Zielbewegungen · Indirekte Sicht · Visumotorische Transformationen Zusammenfassung Präzise Zielbewegungen werden im höheren Berufs-und Le-bensalter langsamer, vor allem bei größerer Weite und höhe-ren Genauigkeitsanforderungen. Darüberhinaus findet sich eine Tendenz zu kürzeren Bewegungen. Besondere Schwie-rigkeiten entstehen möglicherweise bei Bewegungsaufgaben mit indirekter Sicht, etwa bei der Steuerung eines Mauszeigers auf einem Bildschirm oder bei minimal-invasiven chirurgischen Eingriffen. Die bisher vorliegenden Untersuchungen zum Altersverlauf der Anpassung an neue visumotorische Trans-formationen ergeben ein eher inkonsistentes Bild. Die Anpas-sung wird nicht generell schlechter, sondern Alters-veränderungen hängen offenbar von noch weitgehend unbe-kannten Randbedingungen ab. Zu diesen zählen wahrschein-lich die Art der von einer Anpassung beanspruchten Prozes-se, die Art der visumotorischen Transform...
The purpose of this paper is to argue for a particular view of motor learning which is derived fr... more The purpose of this paper is to argue for a particular view of motor learning which is derived from two different sets of data. The first set stems from studies of interference between motor tasks on the one hand and tasks of a more cognitive nature on the other hand, which are simultaneously performed at different stages of training of the motor task. As is evident from the early work of Mohnkopf (1933) and Bahrick and Shelly (1958), the original aim of these studies was to trace the time course of automation. The second set of data stems from correlational studies of individual differences. Originally, these studies were concerned with the prediction of training success in motor tasks, and for this purpose motor performance at different levels of skill was correlated with a variety of other test scores.
Zeitschrift für experimentelle und angewandte Psychologie, 1991
In two experiments the effects of binocular vergence, head tilt, and prolonged gaze inclination o... more In two experiments the effects of binocular vergence, head tilt, and prolonged gaze inclination on the preferred vertical gaze direction were studied. Concurrently, dark vergence was measured to test a hypothesis on the effect that binocular vergence has on the preferred vertical direction of gaze. The previously reported influence of observation distance on the preferred gaze inclination was replicated. When the head was tilted backward, the preferred gaze inclination was lower and the effect of observation distance was reduced; when the head was tilted forward, the preferred gaze inclination was higher and the effect of observation distance was increased. After prolonged upward or downward gaze inclination the preferred vertical gaze direction was shifted up or down, respectively, while the effect of observation distance remained constant. Overall the change of the preferred vertical direction of gaze upon binocular fixation of near stimuli was accompanied by a reduced discrepancy...
Summary In view of the discrepancy between the simple movements usually studied in the laboratory... more Summary In view of the discrepancy between the simple movements usually studied in the laboratory and complex everyday-life motor skills questions arise about generalization. It is argued that generalizability depends on different conditions for different kinds of statements. Generalization of experimental results seems to require a high similarity of the experimental situation to a reference situation, while generalizationi of theoretical statements requires invariance of the system, that is, invariance of functionally defined compnents and their interrelations. Whether or not the conditions required for generalization are fulfilled can never be established a priori, but rather a research strategy is necessary that permits this to be decided a posteriori.
Abstract 1. start with a brief description of the phenomenon [the invariance of relative timing i... more Abstract 1. start with a brief description of the phenomenon [the invariance of relative timing in human movement] and its incorporation into a particular kind of theory, the notion of a generalized motor program/several points of criticism will be discussed that can be raised ...
Publisher Summary Dual-task performance is a field of study where basic and applied research merg... more Publisher Summary Dual-task performance is a field of study where basic and applied research merges. This chapter presents three-step development in dual-task performance. With the development, dual-tasks as a method for the study of general individual-task characteristics, such as automaticity or mental load become obsolete. Instead dual-tasks become a useful method for the study of structures or functions involved in the performance of individual tasks. A final step in the theoretical and methodological development is to apply a more fine-grained analysis to dual-task performance. An adapted control system should realize selectivity, coupling among different output devices, and protection of ongoing outputs. Such adaptation, of course, will turn out to be detrimental to performance in many dual-tasks. Whenever dual-tasks require physically incompatible actions, the available time has to be split between the different tasks. In general, the time-sharing of physically incompatible actions has not attracted very much research effort, but there are exceptions such as monitoring of several different displays.
Publisher Summary To a large extent, coordination depends on the purpose of an action. Mostly, ho... more Publisher Summary To a large extent, coordination depends on the purpose of an action. Mostly, however, the purpose does not specify the required coordination uniquely. Some kinds of coordination are difficult or even impossible to achieve. Thus, in addition to voluntary constraints, there are structural limitations, and within the range of possible coordinative patterns left by voluntary constraints and structural limits, a choice has to be made. This chapter outlines the general perspective on coordination and describes the effects of voluntary constraints and the choice problem. The chapter provides an extended discussion of structural constraints. The models of coordination are presented in the chapter.
Vergence of the eyes in the dark depends on the vertical direction of gaze. In three experiments ... more Vergence of the eyes in the dark depends on the vertical direction of gaze. In three experiments this phenomenon was studied using eye inclinations and head tilts of 5min duration during which monocular or binocular near and distant stimuli were inspected. The effects of eye inclination and head tilt on dark vergence were temporally stable; they exhibited even a tendency to increase with the passage of time. On return to horizontal gaze, positive aftereffects were found, that is. dark vergence was biased towards its value with a vertically deviated gaze. The effect of vertical gaze direction turned out to be additive to the effect of binocular near fixation. These findings represent evidence against the hypothesis that the effect of vertical gaze direction on dark vergence is mediated by a feedforward signal that is related to voluntary effort in raising or depressing the eyes.
Zeitschrift für Arbeits- und Organisationspsychologie A&O, 2007
Zusammenfassung. Von Rosenstiel (2004) hat eine Diskussion zur Fachkultur der Arbeits- und Organi... more Zusammenfassung. Von Rosenstiel (2004) hat eine Diskussion zur Fachkultur der Arbeits- und Organisationspsychologie angestoßen. In dieser Diskussion wurde eine starke Abgrenzung gegen die Grundlagenfächer sowie eine spezifische Publikationskultur gefordert. Beide Entwicklungen bergen Gefahren für das Fach. Die Abgrenzung gegen die Grundlagenfächer sollte durch ein Kontinuum unterschiedlich anwendungsnaher Forschung ersetzt werden; dem entspricht eine überwiegend internationale Publikationstätigkeit, ergänzt durch deutschsprachige wissenschaftliche und anwendungsorientierte Schriften.
A theoretical framework is outlined, according to which structural constraints on bimanual moveme... more A theoretical framework is outlined, according to which structural constraints on bimanual movements can at least in part be understood as coupling between parameters of generalized motor programs. This framework provides a conceptual link between reaction-time data from experiments with bimanual responses, successive unimanual responses, and choice between left-hand and right-hand responses on the one hand and performance data obtained with concurrently performed continuous movements or sequences of discrete responses on the other. On the basis of data obtained with different methods for the study of intermanual interactions, a distinction is drawn between steady-state and transient constraints, and the hypothesis that the tendency to coactivate homologous muscles originates from a transient coupling of program parameters is applied to a variety of observations on performance in different tasks. Finally, the notion of transient constraints is applied to other types of intermanual interdependencies and to interpersonal coordination; the possible emergence of transient constraints from steady-state constraints through progressive development of inhibitory pathways in childhood is discussed, as is the potential biological significance of transient constraints.
The kinematics of leftward and rightward movements are different. The question is raised whether ... more The kinematics of leftward and rightward movements are different. The question is raised whether these differences in both arms are best accounted for in terms of the flexion-extension dimension or the leftward-rightward dimension. In a simple step-tracking experiment the acceleration-time curves of fast flexions and extensions of the left and of the right elbow joint in a horizontal plane were
Evidence for invariant relative timing is mostly based on comparisons between experimental condit... more Evidence for invariant relative timing is mostly based on comparisons between experimental conditions which differ in the average speed of the movements under study. The present experiment examines whether spontaneous variability of acceleration-time curves of aiming movements within a single experimental condition can also be described in terms of variable scaling parameters for both dimensions. This requires that the correlations between peak acceleration and peak deceleration, as well as those between time intervals defined by peak values and zero crossings, are high. In extensions of the elbow joint on a horizontal plane, the latter correlations turned out to be small or even negative. These results cannot be explained as being due to artifacts of several origins. To reconcile them with those based on comparisons between experimental conditions, a dual-level hypothesis of control in aiming movements is suggested. Only variability on one level can be described in terms of variable scaling parameters, and whether or not variability of acceleration-time curves can be described in this way depends on the relative contributions of both levels of control.
Intermanual interactions are modulated by task requirements in the course of motor preparation. I... more Intermanual interactions are modulated by task requirements in the course of motor preparation. In particular, amplitude coupling is strong when identical amplitudes are specified concurrently for the 2 hands but relaxed when different amplitudes are specified. Similarly, directional coupling is symmetric when symmetric directions are specified concurrently but turns to parallel when parallel directions are specified. Here, the author investigated whether the modulations of amplitude coupling and directional coupling in the course of motor preparation are independent or interact. Application of the timed-response procedure, which enables one to manipulate the time available for motor preparation, in 9 participants revealed a weakly interactive pattern. Directional coupling tended to be reduced when different rather than same amplitudes were specified concurrently, and amplitude coupling tended to be reduced when parallel rather than symmetric directions were specified concurrently. In general, interactive effects were also apparent in the rates at which directions and amplitudes were specified. Those observations are consistent with the notion that intermanual amplitude and direction interference are mediated by different but partially overlapping neural structures.
Robotic guidance as a means to facilitate motor learning and rehabilitation has received consider... more Robotic guidance as a means to facilitate motor learning and rehabilitation has received considerable attention during the last few years. However, mixed outcomes suggest that the benefits might be restricted to certain movement characteristics. The authors investigate the effects of robotic guidance on different kinds of motor timing. Two groups of participants performed 2 variants of a circle drawing task in a synchronization-continuation paradigm. One variant was continuous circle drawing (emergent timing), the other variant was intermittent circle drawing (event-based timing). The total duration of movement cycles (absolute timing) and the relative duration of submovements (relative timing) were measured. Half of the participants in each group were guided by a robot device during synchronization (robot-guided group), the other half of the participants received no guidance (control group). Guided participants had superior performance during the synchronization phase with both timing tasks. During continuation there were no benefits of haptic guidance anymore with the continuous circle drawing task. In contrast, with the intermittent circle drawing task guided participants were more accurate in their relative timing than control participants already in the first few trials, and this advantage did not increase in the course of practice. The benefit is thus rather immediate and not cumulative. This finding is consistent with the notion that movement characteristics such as relative timing, which are hard to demonstrate visually or verbally, profit from robotic guidance because of the more accurate demonstrations of the correct movements.
Measurements serve a purpose (and are not a purpose in themselves). This conclusion of Annett is ... more Measurements serve a purpose (and are not a purpose in themselves). This conclusion of Annett is perhaps true for science in general. And it is certainly true for the myriad of measurements taken by the sensory receptors humans are equipped with. Although it is not common to refer to the signals they provide as measurements, for the present purpose I shall call them `natural measurements’. The very fact that humans survive gives evidence of their validity. Consider the problem of assessing the slipperiness of diVerent surfaces an object can be equipped with. Human ®ngertips contain excellent sensors for slipperiness, so one might obtain subjective ratings which are likely to be based on the natural measurements they supply. However, the support of subjective ratings is certainly not the purpose these sensors have evolved for. Subjective ratings are aVected by a number of problems discussed by Annett, but these problems seem not to be rooted in the quality of the natural measurements, but in their calibration and communication which critically involve consciousness and the mapping of states of consciousness on number continua. Therefore, to avoid these problems, would it not be feasible to access the natural measurements not via conscious experience, but via their eVects on those physiological and/or behavioural processes which to support is the purpose they have evolved for? The sensors of the ®ngertips serve the regulation of grip force (cf. Johansson 1996 for an overview). Thus, it should be possible to measure grip forces while objects equipped with diVerent surfaces are lifted and thereby to exploit the natural measurements for the assessment of slipperiness. At least some natural measurements have a characteristic that makes them particularly suited for ergonomics purposes. An example is natural measurement of joint angles, provided by receptors in the joints, ligaments, tendons and muscles. If joint angles are not uniquely speci®ed by the task, humans prefer certain angles over others; speci®cally they tend to avoid the extremes of the range. Formally, this characteristic can be captured by means of cost functions (e.g. Cruse 1986). Even when it is not possible to specify the nature of such costs, the notion of cost functions is useful to capture the fact that certain joint angles are preferredÐwhere costs are lowÐand others are avoidedÐ
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