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Y Guiard

Publications and source records attributed to Y Guiard.

13 recordsLinked to original sources
PubMed2001

Two-handed performance of a rhythmical fitts task by individuals and dyads.

The authors investigated 4 variants of a reciprocal Fitts task in which the pointer was moved to a stationary target, the target was moved to a stationary pointer, or both the pointer and the target were moved to each other bimanually; the bimanual task was carried out either by a single person or by a dyad. Fitts's law held in all 4 conditions, with only minor parametric changes. The kinematic organization varied with task difficulty but remained invariant in task space (i.e., in the mutual frame of reference of the pointer-target system) whatever the pointing condition. In the bimanual conditions, the 2 effectors were coordinated in antiphase with compensatory variability. The authors suggest that the observed chronometric and kinematic patterns emerge from an interplay between simple harmonic motion and the stabilizing influence of the informational flow generated by the closing of the gap between the pointer and the target interval.

Adult↗
PubMed1999

Manual laterality and hitting performance in major league baseball.

Asymmetrical hand function was examined in the context of expert sports performance: hitting in professional baseball. An archival study was conducted to examine the batting performance of all Major League Baseball players from 1871 to 1992, focusing on those who batted left (n = 1,059) to neutralize the game asymmetry. Among them, left-handers (n = 421) were more likely to hit with power and to strike out than right-handers (n = 638). One possible account, based on the idea of hand dominance and an analogy to tennis, is that batting left involves a double-handed forehand for left-handers and a weaker and more reliable double-handed backhand for right-handers. The results are also interpretable in the light of Y. Guiard's (1987) kinematic chain model of a between-hands asymmetrical division of labor, which provides a detailed account of why left batting is optimal for left-handers.

Baseball↗
PubMed1994

Fitts' law in two-dimensional task space.

A traditional continuous Fitts' task may be described as a one-dimensional oscillation between two targets. The combination of two such oscillations along intersecting axes gives rise to a two-dimensional aiming task, allowing the study of the speed-accuracy trade-off in two-dimensional task space. In two experiments subjects were asked to draw as many ellipses as possible while passing through four targets, arranged around the extreme points of the two major axes of a model ellipse. In the first experiment, task difficulty was manipulated simultaneously along the two axes of the ellipse. Regardless of ellipse eccentricity and orientation, movement time (MT) was found to depend linearly on Fitts' index of difficulty (ID), which combines between-target distance and target width. In the second experiment, ID was manipulated independently for the short and the long axes of the ellipse. There was a strong linear relation between MT and ID averaged over the two axes, with the two independent measures of task difficulty exerting interactive effects on MT: the higher the ID on one axis, the smaller the effect of the ID on the other. The present results demonstrate that Fitts' law, only examinated so far in one-dimensional aiming tasks, generalises to two-dimensional task space.

Adult↗
PubMed1993

On Fitts's and Hooke's laws: simple harmonic movement in upper-limb cyclical aiming.

Can discrete, single-shot movements and continuous, cyclical movements be reduced to a single concept? In the classical, computational approach to human motor behaviour, cyclical aimed movement has generally been considered to derive from discrete primitives through a concatenation mechanism. Much importance, accordingly, has been attached to discrete-movement paradigms and to techniques allowing the segmentation of continuous data. An alternative approach, suggested by the nonlinear dynamical systems theory, views discreteness as a limiting case of cyclicity. Although attempts have been made recently to account for discrete movements in dynamical terms, cyclical paradigms have been favoured. The concatenation interpretation of cyclical aimed movement is criticized on the ground that it implies a complete waste of mechanical energy once in every half-cycle. Some kinematic data from a one-dimensional reciprocal (i.e., cyclical) aiming experiment are reported, suggesting that human subjects do save muscular efforts from one movement to the next in upper-limb cyclical aiming. The experiment demonstrated convergence on simple harmonic motion as aiming tolerance was increased, an outcome interpreted with reference to Hooke's law, in terms of the muscles' capability of storing potential, elastic energy across movement reversals. Not only is the concatenation concept problematic for understanding cyclical aimed movements, but the very reality of discrete movements is questionable too. It is pointed out that discrete motor acts of real life are composed of complete cycles, rather than half-cycles.

Attention↗
PubMed1992

The effects of intensity and irrelevant location of a tactile stimulation in a choice reaction time task.

Simon and his colleagues have demonstrated that the location of a stimulus in the sensory field, even if it is irrelevant for the task, may critically affect reaction time. This so-called 'Simon effect' is a general phenomenon that encompasses all sensory modalities. The experiment reported here showed that the tactile version of the Simon effect was additive on reaction time with the respective effects of stimulus intensity and of the within-hand/between-hand composition of the repertoire of fingers devoted to the task. In light of recent theoretical developments, the present data suggest that the locus of the Simon effect is stimulus identification, a perceptual stage which follows stimulus encoding and precedes stimulus-response translation.

Adult↗
PubMed1991

Stimulus-response compatibility and the Simon effect: toward a conceptual clarification.

The current view that the Simon effect (Simon & Small, 1969) reflects stimulus-response compatibility (SRC) is questioned. Previous accounts of the Simon effect have overlooked stimulus congruity (SC), the correspondence relation borne by the two simultaneous aspects of the stimulus, a factor inevitably confounded in the Simon paradigm with irrelevant spatial S-R correspondence. The Hedge and Marsh (1975) reversal effect, replicated in Experiment 1, is reinterpreted as decisive evidence that the Simon effect is entirely accounted for by SC. Furthermore, in Experiment 2 irrelevant S-R correspondence was manipulated in the absence of any variation of SC, and the Simon effect vanished. It is concluded that the Simon effect, contrary to current opinion, represents a spatial variant of the Stroop effect and is irrelevant to the SRC issue. The view that mental operations proceed automatically at the stage of response determination loses one of its strongest empirical arguments.

Adult↗
PubMed1987

Asymmetric division of labor in human skilled bimanual action: the kinematic chain as a model.

This article presents a tentative theoretical framework for the study of asymmetry in the context of human bimanual action. It is emphasized that in man most skilled manual activities involve two hands playing different roles, a fact that has been often overlooked in the experimental study of human manual lateralization. As an alternative to the current concepts of manual preference and manual superiority-whose relevance is limited to the particular case of unimanual actions-the more general concept of lateral preference is proposed to denote preference for one of the two possible ways of assigning two roles to two hands. A simple model describing man's favored intermanual division of labor in the model are the following. 1) The two hands represent two motors, that is, decomplexity is ignored in the suggested approach. 2) In man, the two manual motors cooperate with one another as if they were assembled in series, thereby forming a kinematic chain: In a right-hander allowed to follow his or her lateral preferences, motion produced by the right hand tends to articulate with motion produced by the left. It is suggested that the kinematic chain model may help in understanding the adaptive advantage of human manual specialization.

Journal Article↗
PubMed1984

Writing postures in left-handers: inverters are hand-crossers.

A behavioural approach shows that the inverted hand-writing posture typical of many left-handers is one element of a well-patterned bimanual strategy including (i) counterclockwise rotation of the page; (ii) horizontal orientation of the active forearm on the page; and (iii) positioning of the non-writing hand just below the beginning of the line of writing. The strategy as a whole is liable to represent an adaptation to the necessity of writing with an adduction movement, rather than the symptom of any neurological particularity.

Functional Laterality↗
PubMed1983

Left-hand advantage in right-handers for spatial constant error: preliminary evidence in a unimanual ballistic aimed movement.

While the superiority of the right hemisphere for the processing of spatial relationships in normal right-handers has been largely accepted, it is surprising that evidence for an advantage of the left "nondominant" hand over the right "dominant" hand in spatial motor tasks is up to now almost totally lacking. We report preliminary evidence that normal right-handers perform open-loop ballistic aimed movements with a smaller constant error when using the left rather than the right hand. In addition, constant error is found to be minimal for movements directed toward the left half-field.

Functional Laterality↗
PubMed1983

The lateral coding of rotations: a study of the simon effect with wheel-rotation responses.

A number of experimental studies have consistently shown the locus of spatial S-R compatibility effects to be the selection of the response within an abstract memory code. The purpose of the present study was to test, in the particular case of wheel rotations, the general proposition that any response that a subject internally codes in terms of left and right may be interfered with by the lateral location of the stimuli in a Simon paradigm. Experiment 1 showed that the auditory Simon effect occurred in a task where the subjects had to rotate a steering wheel bimanually either clockwise or counterclockwise according to sound pitch, despite the fact that responses of this kind are undefined with respect to laterality. Experiment 2 confirmed this result in a unimanual rotation condition and suggested that the ear-rotation compatibility effect may be added to the effect of a biomechanical factor, pronation versus supination, supporting the idea of an abstraction motor code. In Experiment 3, subjects rotated the steering wheel with their hands on the lowest part of the wheel. When the response movement made the spot of a C.R.T. move laterally in accordance with the performed rotation, the subjects coded their response directly in terms of its effect on the visual display. For subjects not receiving visual feedback, no compatibility effect occurred. however, the individual data were compatible with the notion that some subjects in this group coded their responses in terms of wheel rotations, and others in terms of hand movements.

Journal Article↗
PubMed1981

Effect of processing mode on the degree of motor asymmetry in the Manual Stroop Test.

In a reaction-time study using conflicting Stroop colour-word stimuli and unimanual-choice responses, Schmit and Davis (1974) have provided data incidentally showing a right-hand advantage for the verbal processing of the material, contrasting with a left-hand advantage for the chromatic processing of the same material. The present experiment successfully replicated the interaction effect, using a within-subject design and a simplified procedure. This effect indicates the preferential involvement of the left hemisphere in the verbal processing of the Stroop material. More interestingly, it shows that it may be efficient to use the very simple laterality factors of the output sphere - such as the hand used to make the response - for the study of hemispheric lateralization of cognitive function.

Color Perception↗