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Biomedical subjects

C Bard

Publications and source records attributed to C Bard.

At least 55 records · Page 3Linked to original sources
PubMed1993

Directional control of rapid arm movements: the role of the kinetic visual feedback system.

Vision has long been considered as a single feedback system providing information about the static and the dynamic features of motor behaviors and of the environment where they take place. However, recent models for oculo-manual movements have included multi-channeling of visual cues (Goodale & Milner, 1992; Jeannerod, 1981; 1984; Paillard, 1980, 1982). According to Paillard's model, a kinetic system, mostly sensitive to dynamic cues, provides directional information of the movement in the rapid distance-covering phase, and a static system, highly sensitive to position cues, provides positional signal errors. The present experiment gives kinematic evidence for the significant contribution of vision during the initial phase of rapid pointing movements when this phase is under the control of the kinetic channel. Movements having directional requirements were more accurate (directional precision) when vision of the initial portion of the trajectory was available. Times-to-peak acceleration and velocity were all shorter and their respective amplitudes were generally higher when vision was available for the first third of the trajectory than when it was not. Further, vision of the entire trajectory did not yield better precision then when vision was available for the initial phase of the movements only. Overall, the data support the existence of two corrective visual feedback systems.

Adult↗
PubMed1993

Determining movement onsets from temporal series.

With the advent of recent measurement techniques, kinematic and kinetic measures commonly are used to describe events over time. Often, the central and peripheral nature of the control processes involved are derived from these temporal series. For example, movement onset often arbitrarily defines the end of the central and the beginning of the peripheral processes. Because of its critical temporal location, we examined whether response dynamics (average movement velocity) affects the determination of movement onset. Interactive graphics and numerical methods of determining movement onsets from temporal series were evaluated on various kinematic signals. Variations in the initial rate of change in a given signal significantly affected the determination of movement onset. Consequently, measurements of component latency must be regarded with caution. A cursory description of related problems elucidated in previous research is discussed, and procedures that can minimize these artifacts are suggested.

Journal Article↗
PubMed1993

On-line versus off-line control of rapid aiming movements.

Recent studies have shown the importance of visual feedback during the rapid initial phase of aiming movements for the control of direction (e.g., Bard, Paillard, Fleury, Hay, & Larue, 1990; Blouin, Teasdale, Bard, & Fleury, in press; Teasdale, Blouin, Bard, & Fleury, 1991). In most of these studies, visual feedback conditions were presented in blocked sessions. Consequently, higher-order processes (e.g., feedforward and/or learning processes), along with on-line processing of visual feedback, might have contributed to the better accuracy found when subjects had visual feedback of only the initial portion of the movements (compared with movements without visual feedback). To test this possibility, we studied subjects' performance of rapid arm movements under different types of presentation (random, precued, and blocked) of the visual feedback conditions of the trajectory (no vision, initial portion only, and vision of the entire trajectory). Directional errors were larger in the no-vision condition than in both conditions with visual feedback. There were no differences among the presentation conditions, suggesting that on-line processing of visual information contributed to the control of the arm movements.

Journal Article↗
PubMed1993

[Surgical treatment of pneumothorax in AIDS patients].

A retrospective review of the charts of 26 patients with the acquired immunodeficiency syndrome (AIDS) treated at the Hotel-Dieu de Montréal was performed. Patients presented a total of 37 pneumothoraces. Eleven cases were recurrent. Bilateral pneumothoraces were documented in three patients, most of them (17) were severe (> 75%). Pneumocystis carinii pneumonia was the most frequently associated pathology. The initial treatment consisted in chest tube drainage. A definitive treatment was indicated in 7 patients with prolonged air leaks (> 10 days) or without lung expansion. Two median sternotomies with bilateral pleurectomies, bullae plication, and talcage were done, and 5 unilateral thoracotomies with pleurectomies and bullae plications were completed. The post-operative survival was variable and related to diseases associated with the syndrome. AIDS related pneumothoraces is a morbid condition which should be treated on an individual basis.

AIDS-Related Opportunistic Infections↗
PubMed1992

Role of afferent information in the timing of motor commands: a comparative study with a deafferented patient.

The accuracy of the motor system in synchronizing simultaneous movements initiations was tested in two conditions: (1) when the motor commands were triggered by an external signal (reactive condition), and (2) when subjects self-paced their movement onsets (self-paced condition). The task consisted of initiating simultaneously ipsilateral finger extension and heel raising. Eight normal subjects and a deafferented patient were tested. In the reactive condition, both normal subjects and the deafferented patient exhibited a precession of finger initiation over heel raising. This delay corresponds to the difference observed in the reaction time of the two limbs when measured independently. It reflects the difference in conduction times of the efferent pathways, as if the two motor commands were released simultaneously through a common triggering signal in the motor cortex. In contrast, in the self-paced condition normal subjects showed precession of heel over finger onsets, suggesting that synchrony is based upon the evaluation of afferent information. Unlike normal subjects, the patient showed no heel precession in the self-paced condition. These findings suggest that reactive and self-paced responses are produced through two different control modes and that afferent information contributes to the timing of motor commands in the self-paced mode.

Adult↗
PubMed1992

Mirror drawing in a deafferented patient and normal subjects: visuoproprioceptive conflict.

Results on a mirrow drawing task showed that a deafferented patient had no problem completing the pattern, whereas normal subjects needed more than four trials to attain a similar performance. The results suggest the presence of integrated visual and proprioceptive maps. The inversion of visual coordinates requires the need for a recalibration. Without proprioception, the task is more like a simple visual tracking task.

Adult↗
PubMed1992

[Attentional requirements for preparing to return a serve in tennis].

Recent studies demonstrated that athletes use more efficient strategies than novices in sports with high perceptual requirements (Abernethy and Russel, 1984; Goulet et al., 1989; Starkes, 1987b). The aim of the present study was to investigate the attentional cost of information processing preceding action in tennis players of different calibers. The dual-task paradigm was used. The primary task consisted of identifying the type of serve (flat, slice, or top-spin) presented on 16-mm file. The secondary task was a manual response to an auditory probe. Results demonstrated that attentional requirements during information processing do not differ between experts and novices. Nevertheless, the experts' results on the primary task are significantly higher than those of novices, whether the primary task is performed alone or simultaneously with the secondary task. The attentional cost of information processed during the ritual phase of the serve is significantly higher than the costs for processing information from the preparation and execution of the serve. It appears, therefore, that attentional input effort is maximal before identification of the most important cues necessary for adequate performance.

Adult↗
PubMed1991

Kinematics of aiming in direction and amplitude: a developmental study.

The patterns of aimed movements to visual targets were analyzed in children aged 6, 8 and 10. Tasks with direction and/or amplitude requirements were used. The tasks were performed both with and without vision. Peak velocity, acceleration and deceleration and their relative temporal occurrence were evaluated. Overall, the 6- and 10-year-olds exhibited higher peak velocity and acceleration when performing the pure directional task than when performing tasks with an amplitude or stopping requirement. On the contrary, 8-year-olds showed similar peak acceleration and velocity across all three tasks. Similarly, when performing the pure directional task, the 6- and 10-year-olds reached their peak velocity and acceleration relatively later in time than the 8-year-olds. Vision of movement increased the peak velocity in all experimental tasks and peak acceleration was increased only in the pure directional task. Thus, movement kinematics varied according to the task requirements and age. Eight-year-olds showed greater propensity to feedback control in all tasks, suggesting an over-inhibition in their approach patterns, whereas 10-year-olds tended to use feedforward processes, with a shortened deceleration phase.

Child↗
PubMed1990

Timing and accuracy of visually directed movements in children: control of direction and amplitude components.

The reaction times (RTs), movement times (MTs), and final accuracy of hand movements directed towards visual goals were measured in 6-, 8-, and 10-year-old children, using tasks in which direction and amplitude components of movement were distinctly required. The tasks were performed with and without visual feedback of the limb. RTs decreased with age, and were shorter in directional than in amplitude task, in all ages. MTs were the longest at age 8 in both tasks, equally short at ages 6 and 10 in the directional task, the shortest at age 10, and intermediate at age 6, when amplitude had to be regulated. In the amplitude task, the target distance generally affected MTs under both visual conditions, but to a lower degree at age 10 than in the two younger groups. Movement accuracy, which was in all cases higher with visual feedback, showed different developmental trends among the two spatial components: directional accuracy was not different among the three groups of age, whereas amplitude accuracy showed a nonmonotonic development in the nonvisual condition, with an increase between age 6 and age 10, and the lowest level at age 8. In the visual condition, amplitude accuracy did not change with age. The specification of direction seems therefore to predominantly load the preparatory stage of the response. Amplitude specification seems to be more dependent on on-going regulations and to undergo a longer and more complex development, with a critical period around age 8 when a greater propensity for a feedback-based control appears on the two components. With increasing age, amplitude tends to be specific to a greater extent by a feedforward process.

Attention↗
PubMed1990

[Metabolic fatigue and the performance of visual tasks].

The aim of this study was to analyse the effects of different types of metabolic fatigue, induced by anaerobic alactacid, anaerobic lactacid, sub-maximal aerobic, and maximal aerobic efforts, on the performance of a sensory task (peripheral threshold detection), a sensory-motor task (coincidence-anticipation), and a cognitive task (recall in central vision). Each of three experimental groups performed one of the above-mentioned tasks under all types of fatigue. Running bouts on a treadmill were used to induce the different types of fatigue. Results show that performance in peripheral vision improves with all types of effort. For coincidence-anticipation, only constant error is affected by anaerobic alactacid and maximal aerobic efforts; the former producing a change in behavior from lateness to anticipation, whereas the latter significantly reduces lateness. Finally, performance in the cognitive task is significantly disturbed by the maximal aerobic exercise. It is suggested that, while sensory and adaptive behaviors improve with previous physical work, cognitive behavior is handicapped by highly demanding activities, that is, activities requiring aerobic maximal efforts.

Adult↗
PubMed1989

[Stability in shooting: the effect of expertise in the biathlon and in rifle shooting].

The aim of this study is to compare the body-gun stability of biathletes and rifle shooters up to the firing of a shot, when shooting in standing position. Eight subjects are tested: two experts and two novices in rifle shooting, two experts and two novices in biathlon. Electromyographic (EMG) activity of the tibialis anterior, gastrocnemius and deltoid muscles, as well as rifle oscillation and centre-of-pressure displacements were recorded during a set of ten shots per subject. The results revealed that expert biathletes seem to use a different strategy than expert rifle shooters, each of them adapting to the characteristics of their respective discipline. No significant pattern emerged from tests with novice rifle shooters, as their scores correlated only weakly with the various parameters measured in this study.

Adult↗
PubMed1988

[Analysis of advance visual indices in receiving a tennis serve].

The aim of this study is to analyse the differential visual patterns of expert and non-expert tennis players preparing to return a tennis serve. Two 16 mm films were used for testing purposes; 27 services were delivered and recorded on each film. The subjects had to identify verbally the type of serve delivered. During film viewing, eye movements were recorded by an Eye Mark Recorder NAC V. Results revealed that the expert players seem to use cues from the general position of the body during the ritual phase and cues from the racquet position during the execution phase.

Adult↗
PubMed1986

Ascites: ultrasound guidance or blind paracentesis?

The classic site for paracentesis in generalized ascites is in the left lower quadrant of the abdomen at a position equivalent to McBurney's point. Its use has an average success rate of 58%, depending on the amount of liquid. To assess the efficacy of paracentesis at this site and to establish the ideal site for blind puncture, we studied 27 consecutive patients with ascites detected by abdominal ultrasonography. The amount of ascites was graded from 1 to 4. Free fluid had accumulated mostly in the perihepatic region, then around the bladder and in the right paracolic gutter, and finally in the left flank. In six of the eight patients in whom fluid was found in the left or right flank, air-filled bowel loops were observed between the abdominal wall and the fluid, in the expected path of a blind puncture. These findings suggest that the safety and efficacy of paracentesis would be greatly improved by ultrasonographic guidance.

Adult↗