The influence of movement segment difficulty on movements with two-stroke sequence

Abstract

Arm movements in the horizontal plane consisting of two segments were examined to determine whether the difficulty of the second segment influenced the kinematic characteristics of the first segment. The direction of the first segment was an elbow extension movement away from the trunk and remained constant throughout the experiment. The direction of the second segment varied between forearm extension and flexion movements. Based on Fitts' law, two different indexes of difficulty (ID) of the second segment were utilized by changing target size and movement amplitude. The effects of changing ID were examined for two different movement amplitudes. All movements were single-joint movements employing elbow flexion/extension and were recorded by an x-y digitizer. Variations in the ID of the second segment produced context-dependent kinematic changes in the performance of the initial segment. Movement duration increased when the ID was increased by reducing target size for both extension-extension sequence and extension-flexion sequences. Peak velocity also decreased for higher ID targets in the extension-flexion sequence. However, there was an interaction between the ID and movement amplitude in the extension-flexion sequence. In this sequence the duration of movement for the high ID/large movement amplitude condition increased substantially compared with the low ID/small movement amplitude condition. In addition, changing ID of the second segment influenced the time between the two segments (intersegment interval) in the extension-flexion sequence. Collectively, these data suggest that the planning of complex movements is based in part on the accuracy demands of multiple segments of the sequence.

Planning short pointing sequences

“…Context effects were observed in drawing line segments with acute angles (Rand and Stelmach 2000;Rand et al 1997;Weiss et al 1997), and in those tasks where reaching a target (Short et al 1996;Sidaway 1991;Sidaway et al 1995) or picking up an object (Gentilucci et al 1997;Marteniuk et al 1987) implied either a sharp change in direction, or an impact on a surface. In all these cases the initiation of one step may be facilitated by a timely use of the elastic energy stored in the muscles while braking the previous step (Guiard 1993, see also Adam et al 1993Meulenbroek and Thomassen 1993).…”

“…the fact that movement times are shorter when movements are performed alone rather than in a sequence, is a form of context effect (Adam et al 2000). However, we adopt here a stricter definition, by referring to context effects only to denote those situations where the cinematic parameters of an earlier phase of the movement are found to depend on the specific nature of the later phases (Marteniuk et al 1987;Rand et al 1997;Rosenbaum 1991). The best known examples of these effects are found in speech, in which the articulatory manoeuvres for uttering a syllable depend on subsequent syllables (cf Hardcastle and Hewlett 1999); 2) in some highly skilled motor tasks such as touch typing (Engel et al 1997;Terzuolo and Viviani 1980;Viviani and Laissard 1996), and Morse coding (Bryan andHarter 1897, 1899), the set of ratios between the duration of the movement components are invariant across variations of the total duration (homothetic behaviour); 3) direct evidence that the timing of the sequence is dictated by a template.…”

Aging and Rapid Aiming Arm Movement Control

“…The measurement of inter-segment-intervals (ISI) is useful in studying human arm movement control (e.g., Burton, 1987;Povel & Collard, 1982;Rand, Alberts, Stelmach, & Bloedel, 1997;Yan, Thomas, Stelmach, & Thomas, 1995). "Pauses" between successive movement segments, which are known as ISIs, generally become longer or more variable if participants' motor control is less developed (Yan et al, 1995).…”

Sequential actions: effects of upcoming perceptual and motor tasks on current actions

“…entire movement sequence (e.g., Henry and Rogers 1960;Khan et al 2008). Specifically, changing the index of difficulty (ID) associated with the second movement (target size and movement amplitude) can influence the kinematics of the first movement (Rand et al 1997). The authors demonstrated that as the ID of the second segment increased there was an increased in the movement time (prolonged time to peak velocity and the deceleration time) of the first segment when performing an elbow extension-extension movement sequence.…”