Relative phase quantifies interjoint coordination.

This note illustrates by example how expression of joint movement on a phase plane can quantitatively describe multijoint coordination during complex actions. Automatic digitisation of high-speed video records was used to obtain lumbar vertebral, hip, knee and ankle joint angular kinematics in the sagittal plane of a subject performing a symmetric two-handed lifting movement. A consistent proximal-to-distal coordination was illustrated via angle-angle and relative phase angle presentations. During bending to pick up a load, the joints began their movement in the order proximal to distal while the reverse order of joint involvement occurred during extension. Phase angle relationships between joints may provide sufficiently sensitive measurements to identify changes in multijoint coordination induced by alterations in task variables such as (in the case of lifting) object mass, lifting height and load moment. Information regarding multijoint coordination is likely to be important in attempting to understand the respective roles and interaction between the bi and monarticular muscles which are involved in everyday complex actions like lifting.

Spontaneous transitions in the coordination of a whole body task.

This paper describes an example of spontaneous transitions between qualitatively different coordination patterns during a cyclic lifting and lowering task. Eleven participants performed 12 trials of repetitive lifting and lowering in a ramp protocol in which the height of the lower shelf was raised or lowered 1 cm per cycle between 10 and 50 cm. Two distinct patterns of coordination were evident: a squat technique in which moderate range of hip, knee and ankle movement was utilised and ankle plantar-flexion occurred simultaneously with knee and hip extension; and a stoop technique in which the range of knee movement was reduced and knee and hip extension was accompanied by simultaneous ankle dorsi-flexion. Abrupt transitions from stoop to squat techniques were observed during descending trials, and from squat to stoop during ascending trials. Indications of hysteresis was observed in that transitions were more frequently observed during descending trials, and the average shelf height at the transition was 5 cm higher during ascending trials. The transitions may be a consequence of a trade-off between the biomechanical advantages of each technique and the influence of the lift height on this trade-off.

Note: A statistical problem in testing invariance of movement using the phase plane model.

Invariant positions on a phase plane of joint angular position and velocity have been proposed as a means by which interlimb coordination may be achieved. This note identifies a problem in the testing, using conventional statistics, of hypotheses derived using the phase plane model. A possible solution is proposed based on directional statistics. Conclusions regarding phase angle invariance, which are based on conventional statistics, must be viewed with some caution.

Visual characteristics of clay target shooters.

A comprehensive battery of standardised visual tests was administered to 11 skilled and 12 novice clay target shooters in an attempt to determine the distinctive visual characteristics of expert performers in this sport. The static and dynamic visual acuity, ocular muscle balance, ocular dominance, depth perception and colour vision of each of the subjects was measured in addition to their performance on simple and choice reaction time, peripheral response time, rapid tachistoscopic detection, coincidence timing and eye movement skills tasks. Expert superiority was observed on the simple reaction time measure only, and the novices actually outperformed the skilled subjects on a number of the other visual measures (viz., static acuity at near distance, dynamic acuity, vertical ocular muscle balance, choice reaction time and rapid target detection discriminability). Scores on all measures for both groups were within the expected normal range indicating that normal and not necessarily above-average basic visual functioning is sufficient to support skilled clay target shooting. An important implication of the finding that skilled shooters are not characterised by supranormal levels of basic visual functioning is the recognition that any attempt to improve shooting performance through training of general attributes of vision to supranormal levels is likely to be unproductive.

The appendix stump: should it be invaginated?

In a prospective trial of 103 patients undergoing appendicectomy, one group of patients had the appendix stump treated by ligation alone and the other group underwent ligation and invagination. The two groups of patients were similar with respect to age, sex, incision and degree of inflammation of the appendix. Perforated appendices were excluded and in neither group were drains used or antibiotics given. No significant difference between the two methods of treatment of the appendix stump was noted, either with respect to wound infection or postoperative stay in hospital.

Cortical fMRI activation to opponents' body kinematics in sport-related anticipation: expert-novice differences with normal and point-light video.

Badminton players of varying skill levels viewed normal and point-light video clips of opponents striking the shuttle towards the viewer; their task was to predict in which quadrant of the court the shuttle would land. In a whole-brain fMRI analysis we identified bilateral cortical networks sensitive to the anticipation task relative to control stimuli. This network is more extensive and localised than previously reported. Voxel clusters responding more strongly in experts than novices were associated with all task-sensitive areas, whereas voxels responding more strongly in novices were found outside these areas. Task-sensitive areas for normal and point-light video were very similar, whereas early visual areas responded differentially, indicating the primacy of kinematic information for sport-related anticipation.

Searching for the minimal essential information for skilled perception and action.

A common concern for both cognitive/computational and ecological/dynamical models of human motor control is the isolation of the minimal essential information needed to support skilled perception and action. In perception isolating essential features of the optic flow field, which are reliably informative regarding the nature of current events, from nonessential features provides a valuable step towards understanding how the computational complexity of perceptual information processing may be reduced to manageable levels and how relatively direct linkages of low dimensionality may be established between information and control variables. Likewise, in the study of action, discrimination of the movement features that remain immutable (invariant?) across changes in task conditions from the variables that are situationally determined provides a principle insight into the structural framework upon which skilled movement is built. Controversy abounds, however, in the study of perception and action as to whether features isolated as informative and immutable are centrally represented (in the form of a template or program) or are rather directly picked up (in the case of perceptual variables) or are simply an emergent consequence of the underlying dynamics (in the case of action variables). In this paper some examples of putative minimal essential information sources in perception and action are provided, strategies for uncovering such sources are discussed, and attention is directed, with the use of some recent data collected on natural skills, to some systematic expert-novice differences in the utilization of essential information and control variables. Expert-novice differences are highlighted because of the insight they may provide regarding the nature of perceptual-motor skill acquisition.

Anticipation in squash: differences in advance cue utilization between expert and novice players.

The time of occurrence and spatial location of the advance cues used to anticipate the direction and force of an opponent's stroke in squash were examined using a film task. This task, designed to stimulate the normal perceptual display of the defensive player, consisted of two discrete parts, each containing 160 individual stroke sequences (trials). In the first part of the film task, the display was occluded at different time intervals throughout the development of the opponent's stroke and the 16 expert and 20 novice subjects had to predict both the direction (down-wall or cross-court) and force (drive or drop shot) of the opponent's stroke. In the second part of the film task, visibility to selected advance cues was occluded by placing opaque mats on the film surface. Across all of the film task conditions experts were superior to novices in predicting the event outcome from the information available, highlighting the important contribution anticipatory skills make to expert performance in this sport. Analysis of lateral (direction) error showed that the most critical time periods for extracting information about stroke direction are the periods between 160-80 ms prior to racket-ball contact and the period of extended ball flight arising at least 80 ms after contact. Whereas both groups were attuned to this ball flight information, only the experts were capable of picking up information from the early part of the opponent's actions. This early information appeared to be provided by the opposing player's arm action. Similar time periods were found to be also important for the prediction of stroke depth, but in this case both experts and novices were similar in their cue dependence.

Expertise, visual search, and information pick-up in squash.

The visual search characteristics of expert and novice squash players were compared in two experiments. In the first experiment subjects were required to predict the forthcoming direction and force of an opponent's stroke from a film display. This film display was designed to simulate the normal display available to the defending player in squash and involved the use of variable temporal cut-offs to force the subjects to use advance cues in their prediction. Systematic differences in the information pick-up of the experts and novices were observed on the film task but these differences were achieved with only relatively minor between-group variations in visual search strategy. In the second experiment, set in the natural field setting, no expert-novice differences in either fixation distribution, order, or duration were observed on a comparable prediction task. This provided further support for the conclusion that the limiting factor in the perceptual performance of the novices is not an inappropriate search strategy but rather an inability to make full use of the information available from fixated display features. Some practical implications of these findings for the squash coach and player are considered.

Expert--novice differences in perception: how expert does the expert have to be?

Twelve expert and 15 novice badminton players viewed a film task which attempted to simulate the perceptual display of the sport of badminton. The film task varied in terms of visibility to either specific time periods of display information or to specific spatial areas of the display, and the subject's task was to determine whether the stroke being viewed had a cross-court or a down-the-line destination. In keeping with an earlier study (Abernethy and Russell, 1987a), expert players were shown to have a unique capability to decrease their prediction errors at an earlier point in the stroke sequence than could novices, but unlike the previous study this could not be attributed to the experts' superior use of arm cues. The robustness of expert--novice differences in perceptual strategy across changes in the level of expert--novice differentiation are discussed.

Cognitive strategies and short-term memory for movement distance and location.

A number of researchers (e.g. Kerr, 1978; Walsh, Russell, Imanaka, & James, 1979) have previously demonstrated interference between location and distance information in motor short-term memory. This interference manifests itself in a characteristic pattern of undershooting and overshooting, with reproduction movement location being drawn in the direction of criterion movement distance and, conversely, the distance of reproduction movements being influenced by the terminal location of the criterion movement. We investigated the effects of different cognitive strategies upon the appearance of this location-distance interference during the reproduction of movement location (Experiment 1) and distance (Experiments 2 and 3) in a linear arm positioning task. Experiment 1 compared performance in location reproduction between two strategy groups differing in the availability of explicit information about the change in starting position. The characteristic undershooting-overshooting interference pattern was observed for the group without the explicit information about the change in starting position but disappeared for the group in which explicit information about the change in starting position was provided. Experiment 2 examined the systematic undershooting-overshooting pattern in distance reproduction for a location strategy (involving some extrapolation of the start and end locations), a counting strategy, and a distance sense strategy (involving the use of visual imagery). The systematic response bias pattern disappeared when the subjects used a location strategy but was clearly observed for the subjects using the other two strategies. This finding was generally confirmed by Experiment 3, which showed a typical undershooting-overshooting pattern in distance reproduction for a counting/distance sense strategy but not for two location strategies (a general location and an explicit location strategy). The location strategies differed in the availability of explicit information about starting and end locations for both the criterion and reproduction movements. The results from these three experiments indicate that explicit information about the start and/or end locations prevents the usual interference between location and distance information from arising in movement reproduction. The notions of automatic and controlled processing and cerebral hemispheric specialization are discussed as potential explanations of these results and of the interference typically observed in motor short-term memory between distance and location information.

Interference Between Location and Distance Information in Motor Short-Term Memory: The Respective Roles of Direct Kinesthetic Signals and Abstract Codes.

Interference between location and distance information in motor short-term memory has been hypothesized on the basis of the systematic pattern of undershooting and overshooting in movement reproduction that occurs when the starting position for reproduction movements is shifted. To determine the possible contribution of limb-specific kinesthetic information to this systematic undershooting-overshooting pattern, we compared the reproduction of linear arm positioning movements performed under either same-limb or switched-limb conditions. Ten subjects were assigned to either a location or distance cue condition, and each subject completed a total of 40 trials, 20 under same-limb and 20 under switched-limb conditions. Each trial consisted of criterion and reproduction movements, separated by a 10-s retention interval. The starting position for the reproduction movement was shifted by 0, 2, or 4 cm in either direction from that of the criterion movement. The systematic undershooting-overshooting pattern, which occurs when either the movement location or distance is reproduced, arose under both the same-limb and switched-limb conditions, suggesting that the primary cause of the location-distance interference is not limb-specific kinesthetic information. Rather, more abstract information in the form of a conceptual memory code appears to be the probable cause of the location distance interference phenomenon.

Toward a quantitative definition of manual lifting postures.

Manual lifting techniques are commonly defined in terms of the postures adopted at the start of the lift. Quantitative definition is problematic, however, because the absolute joint angles adopted to lift an object are influenced by task parameters, such as the initial height of the load. We present an argument for the use of a postural index (the ratio of knee flexion from normal standing to the sum of ankle, hip, and lumbar vertebral flexion) to define the postures adopted at the start of lifting. Stooped postures adopted at the start of a lift correspond to postural indices close to 0, whereas full squat postures correspond to postural indices close to 1. We use angular kinematic data gathered from 71 individuals lifting loads of varying mass from a range of starting heights to illustrate the utility of this index. Although average absolute joint angles were influenced by load mass and initial load height, the average postural index remained unchanged. For example, changes in starting height from 9 cm to 63 cm accounted for between 19% and 67% of the variance in joint positions at the start of the lift but only 1% of the variance in average postural index. This suggests that the postural index provides a method of defining lifting posture that is independent of specific joint positions.

An assessment of the efficacy of sports vision training programs.

BACKGROUND: The claim that sports vision training programs can enhance visual skills and the level of sporting performance was investigated. METHODS: Thirty young subjects were assigned equally to visual training, reading (placebo), and control groups. Visual and motor tests were administered before and after 4 weeks of training or control activity to determine whether any improvements in performance had occurred. RESULTS: Significant improvements on some aspects of vision were apparent for the visual training group, but their improvements in both vision and motor performance were no greater than for either of the other groups. DISCUSSION: There was no evidence for visual training improving either visual or motor performance beyond levels due simply to test familiarity. The benefits of the visual training exercises commonly used by optometrists to enhance sports performance are therefore open to question.

Do generalized visual training programmes for sport really work? An experimental investigation.

We assessed the effectiveness of two generalized visual training programmes in enhancing visual and motor performance for racquet sports. Forty young participants were assigned equally to groups undertaking visual training using Revien and Gabor's Sports Vision programme (Group 1), visual training using Revien's Eyerobics (Group 2), a placebo condition involving reading (Group 3) and a control condition involving physical practice only (Group 4). Measures of basic visual function and of sport-specific motor performance were obtained from all participants before and immediately after a 4-week training period. Significant pre- to post-training differences were evident on some of the measures; however, these were not group-dependent. Contrary to the claims made by proponents of generalized visual training, we found no evidence that the visual training programmes led to improvements in either vision or motor performance above and beyond those resulting simply from test familiarity.

Against relative timing invariance in movement kinematics.

The kinematics of stair climbing were examined to test the assertion that relative timing is an invariant feature of human gait. Six male and four female subjects were video-recorded (at 60 Hz) while they climbed a flight of stairs 10 times at each of three speeds. Each gait cycle was divided into three segments by the maximum and minimum angular displacement of the left knee and left foot contact. Gentner's (1987) analysis methods were applied to the individual subject data to determine whether the duration of the segments remained a fixed proportion of gait cycle duration across changes in stair-climbing speed. A similar analysis was performed using knee velocity maxima to partition the gait cycle. Regardless of how the gait cycle was divided, relative timing was not found to remain strictly invariant across changes in speed. This conclusion is contrary to previous studies of relative timing that involved less conservative analysis but is consistent with the wider gait literature. Strict invariant relative timing may not be a fundamental feature of movement kinematics.

Self-selected manual lifting technique: functional consequences of the interjoint coordination.

The pattern of movement self-selected by 39 subjects to lift light loads from 9 cm above the ground is described in kinematic and electromyographic terms. Hamstring length changes were estimated from hip and knee angular kinematics. Subjects adopted a posture at the start of the lift intermediate between stoop and full-squat postures. A consistent coordination between knee, hip, and lumbar vertebral joints during lifting was described through calculation of the relative phase between adjacent joints and found to be exaggerated with increases in load mass. During the early phase of lifting, knee extension leads hip extension, which in turn leads extension of the lumbar vertebral joints. Early in the lifting movement, when load acceleration is greatest, the erectores spinae are thus relatively long and shortening slowly. Both of these factors produce greater back extensor strength. Rapid hamstring shortening is also delayed, which enhances their strength, and coactivation of the monoarticular knee extensors and biarticular hamstring observed early in the lifting movement suggested that the knee extensors contribute to hip extension through a tendinous action of the hamstrings.